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PPE is something we all must use in the daily life in the hot metals industry either in an operations, mainenance or process role. That said, well WE SHOULD! Sadly I can honestly say that I have visited many plants around the world where PPE is NOT compulsory, either not supplied from management for production use (due to cost skimping), or looked upon as something only 'weaker' people use or employees who are incompetent in their role and a sign that they make mistakes. While this is ridiculous and to be honest and a very unintelligent way of thinking. It exists still in this day and age. There are literally thousands of case studies where PPE has in fact saved lives, avoided permanent scarring or disabilities, not to mention pain, family grief and expensive hospital bills. The use of PPE should be the top priority but always remember its a secondary protection. Of course the primary protection and best protection is not to be there! This week I was very happy to receive samples to use on my global travels from Steel Grip USA. My first impressions of the clothing was that of quality. They are extremely well manufactured. The sizes I discussed also fit perfectly. I'm tall at 6'3" tall with long legs. The trousers I ordered were a 38" waist and a 34" leg. For me its difficult to find safety trousers that fit, however these do perfectly. Steel Grip also had trousers with a longer leg too if required. The Flame Pro :  BF11 9725 T Extended Use Secondary Workwear Shirt The shirts are really well fitting and the materials flame retardant. I'm more than happy to add these garments in my suitcase to take with me on my site visits and process works. Company Hyperlink AC11 1137-45 V11 - Aluminised Jackets from Steel Grip Aluminised Jackets. The aluminised jackets are extremely lightweight and come in either short on long length (the long length is shown above). I specifically requested a short jacket with an non aluminised back to allow for ventilation. I also asked for the push button stud fastening. The jackets packs down nicely into my case for mobility. I'm more than happy to share with my clients the details of these products and contact details of the sales team at Steel Grip. I will add further information on the products when i complete my field trials in the coming days. If you find this article interesting please don't forget to share with your network and add a comment or feedback below. Cheers. George 04/11/25

By 20.05.2020 by Andreas Velling Aluminium is the second most abundant metal on earth and due to its excellent properties, is one of the most widely used metals today. Therefore, it is useful to be aware of the conditions that shorten the lifetime of these metals. Corrosion of any metal can significantly impact its functional strength causing structural damage like cracks, partial fracture, and total material failure in extreme cases. In this article, we shall take an in-depth look into aluminium corrosion to help understand the different types of corrosion that can affect the metal. What is Aluminium Corrosion? Aluminium corrosion is the gradual decay of aluminium molecules into its oxides that degrades its physical and chemical properties. By nature, aluminium is a reactive metal but it is also a passive metal. It means that while nascent aluminium will react with oxygen and water in the environment, the resulting compound will form a layer on the surface protecting the material underneath from further corrosion. This non-reactive oxide layer sticks well to the surface and does not flake off easily, similarly to stainless steel. Unlike deliberate processes like laser etching, aluminium anodising, or brightening, corrosion is a slow process and will occur over many months or years. What makes aluminium unique though is that there are many different types of corrosion pathways. Understanding these different corrosion phenomena is the first step in applying control measures to reduce or completely prevent their occurrence. Types of Aluminium Corrosion Atmospheric corrosion The most common form of aluminium corrosion. Atmospheric corrosion of aluminium occurs as a result of exposure to natural elements. Due to its possibility of occurring in most places, atmospheric corrosion forms the lion’s share of the total damage caused to aluminium in the world by all types of corrosion combined. Atmospheric corrosion can be divided into three subcategories. These are dry, wet and damp, depending on the moisture levels of the service environment. As the moisture content can change quite a bit depending on your geographical location, some regions will observe greater corrosion than others. Other environmental factors that affect the extent of atmospheric corrosion are wind direction, temperature and precipitation changes. Concentration and variety of pollutants in the air, closeness to large water bodies, etc. also play a significant role. Atmospheric corrosion may be exacerbated if the design does not allow for drainage of moisture. Creating pockets of water for rain and condensation, for example, are harmful design flaws. Galvanic corrosion Galvanic corrosion, also known as dissimilar metal corrosion can affect aluminium when it is physically or through an electrolyte connected to a noble metal. The noble metal can be any metal that has lesser reactivity compared to aluminium. Reactivity of a metal depends on its position in the electrochemical series. The severity of corrosion will be worse if the other metal is further away from aluminium in the electrochemical series. The intensity of corrosion is highest at the intersection, where the two metals meet, and reduces as we go further away from this interface. For example, if aluminium and brass are in contact or even close to each other and placed in seawater, a galvanic cell is formed. Then the aluminium part will corrode as it acts as the anode (positive terminal). This can be a problem in boats where brass fittings may be close to aluminium fittings while they are both immersed in seawater. The electrons flow from aluminium to brass through the seawater. This type of galvanic cell may be inadvertently formed in other service environments and lead to galvanic corrosion. Galvanic corrosion can be much quicker than normal atmospheric corrosion. Pitting corrosion Aluminium pitting corrosion Pitting corrosion is a surface corrosion phenomenon of aluminium metal characterised by small holes (pits) on the surface. Usually, these pits do not affect the strength of the product. Rather, it is an aesthetic issue but can lead to failure if surface appearance is critical. Pitting corrosion generally occurs in regions where salt is present in the atmosphere, as the presence of chloride anions is responsible for it. Sulphate salts can also cause pitting corrosion to some extent. The worst case of pitting corrosion is observed in the presence of alkaline and acidic salts. For pitting corrosion to occur, the alloy’s potential must be above the electrolyte’s (salt solution) potential. The existence of surface defects at grain boundaries and second-phase particles is a precursor to pitting corrosion. Crevice corrosion Aluminium crevice corrosion Crevice corrosion is a form of localised corrosion process in materials. Overlapping materials or unintentional design mistakes can lead to the formation of crevices. As a result, collecting seawater into those pockets can lead to crevice corrosion. Even a small gap between a bolt and the structure is enough for this type of corrosion to begin. As time passes, aluminium from the material dissolves and precipitates into seawater. This ionic aluminium absorbs oxygen from the surrounding air and hydroxide ions from the electrolyte, forming aluminium hydroxide. This oxygen reduction makes the crevice acidic in the presence of chlorides which accelerates the rate of corrosion. Intergranular corrosion When it comes to aluminium, the grain boundary is electrochemically different compared to the alloy microstructure. This causes an electrochemical potential set up between the two and an exchange of electrons takes place. There are multiple variations of intergranular corrosion based on thermochemical treatments and metallic structures. It is also found to different degrees in different series of aluminium alloys. The 6xxx series alloys, for instance, are relatively less susceptible to this type of aluminium corrosion. The anodic path will vary with different alloy systems. While in the 2xxx series it appears as a narrow band on either side of the grain boundary, in the 5xxx series it is manifested as a continuous path along the grain boundary. Like pitting corrosion, intergranular corrosion begins from a pit. However, it propagates far more quicker along susceptible grain boundaries. Exfoliation corrosion Exfoliation corrosion is a special type of intergranular corrosion found in aluminium alloys that have marked directional structures. This is predominantly evident in aluminium products that have undergone hot or cold rolling processes. It occurs along elongated grain boundaries in the microstructure. The term exfoliation comes from the fact that the corrosion product is more voluminous and gives the impression of lifting from the material surface. This type of aluminium corrosion expands above the surface as well as sideways building up stresses in the product. In turn, this causes a wedging action initially at the surface before it migrates into the bulk of the product. Severe delamination takes place and the material weakens. Surface degradation results like pitting, flaking, and blistering can occur. The 2xxx, 5xxx, and 7xxx series are more prone to exfoliation corrosion due to their highly directional grain structures. This makes the grain boundaries far more sensitive to intergranular corrosion. The susceptibility to exfoliation corrosion can be modified by using heat treatment methods to redistribute the precipitates. General corrosion When corrosion takes place almost uniformly on an aluminium product surface, it is uniform or general corrosion. This type of corrosion can happen with products constantly exposed to a highly acidic or alkaline medium. It may also occur in the presence of high electrochemical potential while the product is in an electrolyte. A typical example is rusting of an aluminium plate in an acidic solution. Uniform corrosion is the result of the continuous shifting of anode and cathode regions in contact with the electrolyte which manifests as a uniform corrosive attack on the surface. In high and low pH solutions, the oxide layer is also unstable and does not protect the metal underneath. The thickness of the material reduces and it will eventually dissolve completely. The attack is not completely uniform and there will exist peaks and valleys. The absence of small deep corroded areas is enough to term it as a general corrosion example. Deposition corrosion Deposition corrosion occurs when a dissimilar metal gets deposited on the aluminium surface leading to serious localised corrosion. Imagine water flowing through copper tubing. When the water flows through, it picks up copper ions. These copper ions are now in a solution. When this solution comes into contact with an aluminium surface or vessel, it deposits these copper ions onto it. These ions now form a subtle galvanic cell which corrodes the aluminium through pitting if the ions are lower in the electrochemical or galvanic series. The larger the difference between aluminium and the deposited ion in the galvanic series, the worse the corrosion. Even a concentration of 1 ppm copper ion solution is known to perform serious corrosion on the aluminium surface. The metals that can cause deposition corrosion of aluminium are referred to as ‘heavy metals’. Some important heavy metals are copper, mercury, tin, nickel, and lead. The corrosion caused by this method is more pronounced in acidic solutions as compared to alkaline solutions. This is because these ions have low solubility in alkaline solutions. Stress corrosion cracking (SCC) Aluminium stress corrosion cracking Stress corrosion cracking (here on out referred to as SCC) is a form of intergranular corrosion that can result in the total failure of aluminium parts. Three conditions need to be fulfilled for this corrosion to occur. A susceptible alloy is the first of them. Not all aluminium alloys are equally prone to SCC. High yield strength alloys are more likely to suffer from stress corrosion cracking. The second condition is that the service environment must be humid or wet. The third condition is the existence of tensile stress in the material. This tensile stress is responsible for the opening of the crack and its propagation through the metal. There are two types of SCC processes. The first is intergranular stress corrosion cracking (IGSCC) in which the crack propagates along the grain boundary. The second is transgranular stress corrosion cracking (TGSCC) where the crack travels through grain bodies and not along the boundaries. Erosion corrosion Erosion corrosion of aluminium Erosion corrosion of aluminium is caused by the impingement of a high-speed water jet on the aluminium body. Two factors that aggravate erosion-corrosion are the velocity of the water and its pH level. The existence of carbonate and silica content in water can further augment the corrosion rate. In pure water, aluminium corrosion proceeds at a sluggish rate. But when the pH level exceeds 9, this rate increases. In acidic water, corrosion is faster. Erosion corrosion can be prevented by controlling the above factors. Either reducing the water velocity, or maintaining water quality, or both can significantly reduce erosion-corrosion. Improving the water quality means maintaining the pH level as close to neutral as possible (<9), and reducing silica and carbonate content. Corrosion fatigue It is a well-known fact that fatigue can cause the complete failure of a product if left unchecked. In the case of aluminium, fatigue cracks can act as initiation sites for pitting corrosion. Corrosion fatigue in aluminium occurs when it is repeatedly subjected to low stress for long periods of time. The crack initiation and propagation takes place with greater ease in a corrosive environment like seawater and salt solutions. Corrosion fatigue cannot proceed without the presence of water in the atmosphere. It also remains largely unaffected by stress direction as the crack propagation is mostly transgranular. Thus, the stresses do not affect its propagation unlike in the case of SCC. Filiform corrosion Filiform or wormtrack corrosion is initiated as pitting corrosion. It starts at points where the paint has peeled off the surface of the aluminium. The reason could be scratches or bruises on the surface that expose the underlying metal surface. Filiform corrosion occurs and spreads easily in the presence of chloride anions and high humidity. Though it initiates as saltwater pitting corrosion, the mode of propagation is that of crevice corrosion. The head of the wormtrack is acidic and has high chloride content. It absorbs oxygen and acts as the anode. The latter part of the wormtrack acts as the cathode and the reaction ensues. Filiform corrosion can be prevented by keeping the surface free of damage and closing all the small gaps using paint or wax. The relative humidity of the environment must be reduced if practical. Microbiological induced corrosion Microbiological induced corrosion or MIC is corrosion caused due to microorganisms/fungi. This type of corrosion is noticed in fuel and lubrication oil tanks. In the presence of water in oil, microbes and fungi can thrive. Some of these organisms are capable of consuming oil and excreting acids that can cause corrosion of the aluminium vessel used for storing. This acid causes pitting corrosion in the aluminium vessel, eventually leading to leakage. To prevent this, the oil must be purified as far as possible to remove water content. Draining water at regular intervals from fuel tanks after purification is also necessary. If improving the fuel quality is not an option, using fungicides is possible to prevent germination. Many thanks to Andreas for allowing me to use this article on the site. I'm sure its of great interest to the readers and users of aluminium. The original article can be found here with many other interesting topics. Aluminium Corrosion LINK Thanks for reading this short 5 minute blog and please feel free to get in touch and find out more. albertech@gmail.com Please leave feedback in the comments below.

What are alloy hardeners and why do we add them to pure or primary aluminium? By the very term alloying hardeners, to can imagine why the first series of alloying ‘ingredients’ were added to pure aluminium. Adding alloys or a combination of alloys began because of several discoveries on the use of primary aluminium for industrial applications. Aluminium in its pure form has low strength, limited conductivity, ductility and viscosity (required for die casting). Pure aluminium has a yield strength of only 15MpA when compared to wrought Iron (around 150Mpa) you can see how it is limited for some applications, therefore adding ‘hardeners’ can modify the behaviour of aluminium . These alloys can be categorised as “major” alloying additions. Sadly some of the effects were positive however some not so and other alloying elements we used to counter or cancel these detrimental effects this can be known as “minor” alloying additions. Used in combination the addition of alloying elements to aluminium is the principal method used to produce a selection of different materials that can be used in a wide assortment of packaging, structural, aerospace and automotive applications. And so the Metallurgist is born. When we refer to an aluminium series we know specifically the alloying ‘major’ addtions based upon the series quoted. For example 1xxx series – Primary / pure aluminium >99.00% 2xxx Series – With the addition of Copper (Cu) 3xxx Series – With the additions of Manganese (Mn) 4xxx Series – With the addition of Silicon (Si) 5xxx Series – With the addition of Magnesium (Mg) 6xxx Series – With the addition of Mg and Si 7xxx Series – With the Addition of Zinc (Zn) The principles of the addition of these elements to aluminium are as follows. 2xxx Series (Copper Additions Cu) Typically the aluminium Copper (AlCU) alloys contain between 2% and 10% copper and sometimes containing other minor elements to give additional properties to the final product. The copper facilitates precipitation hardening and adds substantial strength to the aluminium alloy. The addition of Cu reduced ductility of the alloy and also reduces corrosion resistance. Aluminium / Copper alloys are more prone to solidification cracking with an increase in the Cu content within the alloy. It is not unheard of for large cast AlCu slabs to crack even after several hours have past since casting. Welding of Cu alloys is difficult but Al Cu alloys are some of the highestst strength aluminium alloys known with applications ranging from defence (military vehicles) to aerospace.   3xxx Series (Manganese Additions Mn) The addition of manganese to aluminium increases strength through solution strengthening and improves strain hardening while not appreciably reducing ductility or corrosion resistance. These are moderate strength non heat-treatable materials that retain strength at elevated temperatures and are seldom used for major structural applications. The most common applications for the 3xxx series alloys are can bodies, cooking utensils, radiators, air conditioning condensers, evaporators, heat exchangers and associated piping systems. 4xxx Series (Silicon Additions Si) The addition of silicon to aluminium reduces melting temperature and improves fluidity. Silicon unlike many other additions soes not form an intermetallic compound with aluminium. Silicon alone in aluminium produces a non heat-treatable alloy; however, in combination with magnesium it produces a precipitation hardening heat-treatable alloy. Consequently, there are both heat-treatable and non heat-treatable alloys within the 4xxx series. Silicon additions to aluminium are commonly used for the manufacturing of castings. The most common applications for the 4xxx series alloys are filler wires for fusion welding and brazing of aluminium. 5xxx Series (Magnesium Mg) Magnesium is added to aluminium to increase strength through solid solution strengthening and increases the strain hardening ability. Al Mg alloys are the strongest of the non heat treatable alloys and are therefore used in many structural and construction applications. 5xxx series aluminium is generally cast as a flat rolled product (sheet or plate) for the workability and strengthening mechanism and rarely cast as an extrusion billet due to the work hardening during the extrusion process and the difficulty that brings. Common applications for the 5xxx series alloys are Can End Stock (CES), truck and train bodies, construction and buildings, defence / armoured vehicles, ship building, chemical tankers, SCUBA, pressure and cryogenic tanks. 6xxx Series (Magnesium and Silicon Mg / Si) The addition of magnesium and silicon to aluminium produces the compound magnesium-silicide (Mg2Si). The formation of this compound provides the 6xxx series their heat-treatability. The 6xxx series alloys are easily formed and ductile and therefore often used in extruded profile shapes. These alloys form an important complementary system with the 5xxx series magnesium alloys. The 5xxx series alloy used in the form of plate with the extruded profile form often joined to the plate. Common applications for the 6xxx series alloy include, construction materials (windowframes) automotive parts (crash protection, safety and components), scaffolding, handrails, drive shafts, bicycle frames, ladders and lawn furniture. 7xxx Series (Zinc Zn) The addition of zinc to aluminium (in conjunction with some other elements, primarily magnesium and/or copper) produces a heat-treatable alloys exhibiting some of the highest strengths. The zinc substantially increases strength and permits precipitation hardening. Some of these alloys can be susceptible to stress corrosion cracking and for this reason are not easily welded. Because of the high strength of Zn alloys they are often used in military applications. Some other common applications include aerospace, vehicle panels, baseball bats and bicycle frames. Below are some other elements added to aluminium to change its mechanical or physical parameters. Iron (Fe) Iron is the most common impurity found in aluminium and is intentionally added to some pure (1xxx series) alloys to provide a slight increase in strength. Common Fe levels in primary metal range from 0.07 to 0.20wt%. Titanium (Ti) Titanium is added to aluminium primarily as a grain refiner. The grain refining effect of titanium is enhanced if boron is present in the melt or if it is added as a master alloy containing boron largely combined as TiB2. Titanium is a common addition to aluminium weld filler wire as it refines the weld structure and helps to prevent weld cracking. Chromium (Cr) Chromium is added to control grain structure, to prevent grain growth in aluminium-magnesium alloys, and to prevent recrystallization in aluminium-magnesium-silicon or aluminium-magnesium-zinc alloys during heat treatment. Chromium will also reduce stress corrosion susceptibility and improves toughness. Nickel (Ni) Nickel is added to aluminium-copper and to aluminium-silicon alloys to improve hardness and strength at elevated temperatures and to reduce the coefficient of expansion. Zirconium (Zr) – Zirconium is added to aluminium to form a fine precipitate of intermetallic particles that inhibit recrystallization. Lithium (Li) The addition of lithium to aluminium can substantially increase strength and, Young’s modulus, provide precipitation hardening and decreases density. Lead (Pb) and Bismuth (Bi) – Lead and bismuth are added to aluminium to assist in chip formation and improve machinability. These free machining alloys are often not weldable because the lead and bismuth produce low melting constituents and can produce poor mechanical properties and/or high crack sensitivity on solidification. Very much restricted in use due to health related implications. Summary The aluminium association has over 400 registered wrought alloys in circulation and over 200 casting alloys each with its own benefits and mechanical behaviour. Careful selection of the alloy is required for any application and each will come with its pro’s and cons and castability, rollability and extrudability. Thanks for reading this short 2 minute blog and please feel free to get in touch and find out more. The blog is written based upon academic and vocational training and through research papers presented in global forums and available in the public domain. I have taken advise from present and former technical colleagues and with my own insights from experience in the field and in the casthouse. albertech@gmail.com Please feel free to leave feedback in the comments below.

Its a question put to many production and process employees from the sales and, more importantly from the senior management team "How good is our actual product quality"? Sales are always looking to differentiate and gain an angle to increase their upcharge sale price or lever upon "our better than - competitors quality", and why not! When we look at extrusion billets the quality can vary depending upon a number of important factors, however these factors are all controllable by good process housekeeping and an experienced team. Be they chemical, metallurgical, physical or a combination of all three. Final processing of the billets at your customers premises, well, their own recovery is very much dependant upon you, the supplier, and how you manage your own internal process. You process must be robust, repeatable, controlled, data driven and have some kind of closed loop assessment. This is clear and the casthouse is very much a good starting point. However don't neglect procurement right back to buying and receiving good alloying hardeners, material inspection, furnace preparation, casting, homoginisation and of course QA inspection. Over the years I have worked on several projects to benchmark industrial standards covering all the major, minor and influential aspects of quality and quality control to ensure that the equipment is maximised not only for production volume, but also for repeatability and reproducibility of critical parameters thus ensuring a robust product delivered to the client. Some key pointers would be as follows and a good starting point : Chemical Fe Content : Influences the billet colour and streaking on the extruded profile, careful adherence to the chemical limits is important, not only for Iron but for all major, minor and some trace elements. Consider using "internal limits" to ensure confirmation. A good practice would be to have an internal concession for anything outside internal limits. Secondly, Fe is a component in the creation of intermetallic particles of Al-Fe-Si which are situated on the grain boundary within the billet microstructure. The quantity of Al-Fe-Si intermetallic can affect the extrudability of the billet, in particular the surface quality. This effect can be exacerbated if billets are not homogenized following a good recipe. When we consider the alloys 6005, 6061 and 6082 alloys the effect of Fe is comparable, it is not as pronounced nor as critical as for 6060 and 6063 alloys, simply because the greater overall level of alloy content, and the customers final application. Si and Mg Content : These two alloys aid and influence the mechanical strength of the extrusion (the hardness and physical strength), the precipitation of the constituents during the homoginisation process give the product its strength. Again the alloy composition and raw material quality is critical to maintain the properties of strength for the client. His extrusion speed and pressure can b directly linked to the alloying. Metallurgical Mn Content : This element has an influence on the phase transformation undertaken during the homoginisation process and promotes the transformation of β-phase of Al-Fe-Si intermetallic particles into ɑ phase again during the heat treatment. The β-phase has much rougher structural ‘needles’ on the microstructural level which negatively influences die-life cycle during extrusion process. As ɑ-phase Al-Fe-Si intermetallic particles are more spherical – so the wear to the die is less and the die-life cycle is higher. The transformation from β-phase to the ɑ-phase as a minimum should be greater than 95%. Hydrogen Content : Target Hydrogen ≤ 0.20 (target 0.15) cm3 per 100 g Al. Measured generally with an AlSCAN or similar. Inverse Segregation Zone (ISZ) should be ≤ 100 µm, generally this is achievable for diameters up to 9" (228mm), for larger diameters ISZ can be as great as 200 µm. Metal cleanliness is particularly important for architectural and automotive applications but should be robust and common for your entire process. Good process control and production 'housekeeping' will help in keeping your inclusion count to limits that wont effect your customer. In terms of quantative numbers as a rule of thumb PoDFA ≤0.15 mm2/kg with a target ≤0.1mm2/kg. Solid non-metallic inclusions (SONIM's) ≤0,02 мм2/kg Oxide films should be limited and discussed prior to prodct release.- The size of the TiB2 agglomerates ≤10 µm Physical Physical measurements and tolerances are paramount to the billet extruder to maximise recoveries and minimise customer to customer variation. One parameter that can be easily overlooked is the sawn edge roughness of the log. This parameter will effect how the billets butt together during the extrusion process with the client. A good rule of thumb is to have a sawn end surface: Ry ≤ 15 µm. Avoid any mechanical damages, these can be picked up from handling equipment either pit lifting, down ending, rollers or physical damage from FLT transportation. Avoid any organic stains from saw hydrocarbons, rust marks from banding or any dust. No oxide films and inclusions (patches) on the surface. Homoginisation saddle marks are generally unacceptable and ugly and should be thoroughly investigated if they appear on the log. Quality Control We mentioned Hydrogen measurements, however we did not touch on inclusions, this topic alone almost warrants a separate subject (maybe in another blog post!) but nevertheless it is significant in the performance and reputation of your extruded or post cast products. Alberg can help on inclusion reduction, pin point sources and describe international best practices. We understand acceptable PoDFA levels and can drop your count without expensive interventions such as inline treatment, process disruptions or switching suppliers for raw materials. We have a simple process which can lead to excellent results. In summary Obviously this is only a very small snap shot of observations and process control required to satisfy you customers and give you something to think about while casting billet products. www.alberg.tech has industrial best practice knowledge and real benchmarking experience to ensure we can help you develop and grow your own internal process. Alternatively as an extruder of billets, we can work with and advise your suppliers on how to make your extrusions perform better increasing your level of satisfaction and gaining on the overall yield. Many thanks for taking the time to read this blog, please feel free to share with your friends and colleagues. Should you still require further help on this particular subject reach out and please contact : albergtech@gmail.com George

Please read part 1 of a 3 part series on billet extrusion and defect identification. The ductility of aluminium makes it an ideal material for low temperature die extrusion. At temperatures of between 450'C to 500°C, approximately 80% of the melting point for of 6xxx series aluminium. The billet loses its strength and becomes extremely ductile and pliable with good formability. This ductility allows the aluminium billet to be 'squeezed' like toothpaste through a hardened steel die by applying a lateral pressure forced through by a hydraulic ram as shown below. The container wall retains any outward pressure and thus forces the material through the die opening or bearing. Aluminium alloy heat treatment is called “Age Hardening” and/or “Precipitation hardening and this is the method from which we will reach the desired strength in 6xxx billet extrusions. 6xxx or 'Al-Mg-Si' alloys represent approximately 90% of all extruded aluminium volume. AS discussed above this is purely down to the nature of the alloy, being relatively soft at high temperatures. Further treatment will give useful strength when artificially aged and the alloy has a large “working range” that allows them to be both extruded at high speed and solution treated at the press. The series has good finishing response to coating or anodizing, the alloy is formable, machinable and demonstrates good corrosion resistance. What happens in the extrusion press? Approximately 95% of the mechanical work done during the extrusion deformation process is converted into HEAT as can be shown in the schematic above. This heating occurs as the metal is squeezed through the die and deformed, this has an impact on the grain structure due to recrystallisation that we shall discuss later in the blog. The deformation will cause the billet temperature to Rise between : 82'C to 132'C The die exit temperature of the profile can reach : 549'C to 571'C and in approximately less than < 20 seconds During the extrusion process transformation the temperature of the profile rises above the solvus temperature of the alloy this in effect allows the Mg2SI precipitates to dissolve and enables the final properties of the extruded alloy to reach its required T6 condition, i.e. solution treated and then artificially aged. During the time above the solvus condition the alloy recrystalises even after the grain were previously deformed in the direction of the lateral press. The 'working range' of the billet is defined by the solvus and melting temperature of the alloy being extruded and as a general rule of thumb the bank becomes narrower with an increase in alloy content. Preheating the billet There are two main reason to preheat a billet prior to extrusion. The first one to take the metal to a temperature at which point it is soft and pliable enough for the press to extrude it through the die. This is directly linked to the die exit temperature of the press during the push and as we discussed above is determined by the solvus and melting point of the alloy. This exit temperature can also be controlled by the ram speed / press speed. The second to establish a temperature platform from which the extrusion temperature rise can take the metal above the solvus. Careful awareness is required to ensure that when the billet temperature is changed the alloy microstructure attempts to reach equilibrium - often this means Mg2Si particles grow and this can effect the overall strength and performance of the extrusion. Long preheating cycles offer up no advantages and in reality the preheat times should be as short as possible thus giving a better extrusion yield and minimising energy costs. Failure to dissolve Magnesium Silicide (Mg2Si). As we mentioned during the billet preheating temperature (>450'C) the magnesium silicide begins to re-precipitate in the billet, Mg2Si is detrimental to the extrudability of the billet as it is a strengthening mechanism it can also exacerbate die wear for the extruder. Mg2Si precipitates can also effect the cosmetic appearance of the profile particularly when anodising or with colour treatments. It is therefore important to dissolve these re-precipitates and the table below shows the exit die temperatures used to successfully do this. Recommended die exit temperatures: Use a remedial or recovery practice for billets inside heater, during long stoppage or heater shutdown also shown in table 1 above. If you see an undesired increase in the profile strength or surface finish / anodising problems then revisit casting, homogenisation parameters as well as the extrusion preheating and the die exit temperatures. Some possible reasons could include: - Extended preheat soak in the range 325'C - 425'C - Low die exit temperature - Low core temperature on large profile extrusion - Low billet preheating temperature - Coarse homogenized structure from the supplier Press Quenching Upon exiting the die the extrusion is at solution heat treatment temperatures so it is quenched using air or water to form solid solutions in the extrusion so that the alloy extruded responds to “aging”. The alloy type and required temper defines the “critical quench rate” and the “critical cooling range”. The quench rate used should be a is a balance between mechanical properties and shape control. See below an example for 6063 alloy. Quench Data for Al-Si-Mg alloys Depending upon the alloy will determine the required quench rate and also the type of quench required. It would be desirable to have a forced air quench for alloy 6061 where a 6063 alloy can be quenched with standing / still air, of course this very much linked to the profile mass / thickness being extruded. To be continued. Thanks for reading this short 5 minute blog and please feel free to get in touch and find out more. The blog is written based upon academic / vocational training and through research papers presented in global forums and available in the public domain. I have taken advise from present and former colleagues and with my own insights and learnings from experience casthouses I've worked and in the field. albertech@gmail.com Please leave feedback in the comments below.

Close control of the cast structure is a major requirement in the production of high quality aluminium alloy castings. The most effective way to provide a fine and uniform as-cast grain structure is to add nucleating agents to the melt to control crystal formation during solidification. Grain Refiners with a number of different relationships i.e. the titanium to boron, titanium to carbon or titanium to aluminium. Grain refinement in any wrought alloy can be discussed as to its overall ‘requirement’, feed rate and final application necessity. Sure, the grain refinement manufacturing companies will insist on its use and quote some supporting statistics, faster casting speeds, greater fluidity, better mechanical properties, improved surface quality etc etc…. But in reality, for an extrusion product that goes through multiple heat cycles and is squeezed through a die and pulled and stretched does an 'accurate' grain size post cast really matter and therefore do we really need to add so much refining agent. Some thoughts of mine for discussion. I have spent a significant amount of time looking at the need for grain refinement and curtailing its use to the bare minimum while achieving good castability while achieving the customers specification. Balancing the feed rate accurately can save millions of dollars per year for the large casthouses and organisations. Many casthouses and process engineer frequently over ‘inoculated’ the cast, with a 'just in case' mentality. When what were really saying is “heck, I don’t buy the stuff so what difference does it make, better to be safe than sorry right”? No, not at all. Over feeding grain refinement serves no purpose at all and in fact can be detrimental to the product increasing the TiB2 “inclusion” levels and possibly introducing detrimental oxides Al2O3 into the billet, depending upon the supplier of the raw material. Compounding the fact that were just wasting money and adding to the overall product conversion cost! In practical terms the best choice of grain refining agent and addition rates depend upon several factors, being. 1) The supplier 2) Casting process, casting speed and metal temperature 3) Composition of the alloy 4) Furnace Ti levels prior to inline feeding 5) Flow rate of the metal 6) Diameter of the billet (greater the billet diameter the higher the consumption), all molds being equal 7) Final product application Lets first look at the mechanisms to grain refine and take an example of AlTiB 5/1. Firstly, what does that actually mean "AlTiB5/1".? Well, it relates to the ratio of Aluminium, Titanium and Boron. In this example the amount of Titanium is 5% and 1% is Boron additive with the remainder being hopefully pure aluminium (or as near as possible). You will see similar compositions of 3:1 and 5:0.2 and so on. Aluminium in its liquid form (T°C above 660°C) requires a substrate for heat extraction for the mechanism of solidification to exist, turning our liquid into the solid form we require for a semi finished products. In this case an extrusion billet. This transition can be the primary cooling effect of the mold wall of the container, an inclusion or ‘the self-imposed’ inclusion that is boron from the refining agent. The solidification principles are predominantly the same, well to a point. The boride particles in the grain refiner act as the nucleation substrate, the borides are present as insoluble particles, typically 1-2μm in size. These boron particles exhibit a thin layer of Al3Ti, it is upon this excess titanium that the nucleation and growth of the aluminium crystals begin. “Excess” titanium is required to make the refiners work this can be added in the refining coil and also as a bulk refiner in the furnace. (typically 100 to 150ppm) works well. The balance between furnce Ti and RGF (Rod Grain Feeder) is the key to success! I have seen over the years that different types of grain refiners and even different suppliers have varying levels of efficiency. A typical average grain size per refiner addition can be seen below in the chart from W.A. Schneider et al. - Light Metals 2003. If you’re not feeding the grain refinement in the range above then something is wrong and this is costing you a lot of money. Thanks for reading this short 2 minute blog and please feel free to get in touch to find out more or book a site visit and consultation. albertech@gmail.com Thanks for reading.

I'm sure you know that the 6000-series alloys are most frequently used for extrusion. Commonly AA6060, 6061, 6063, 6182 and 6005. Silicon-Magnesium alloys provide a good balance of strength, corrosion resistance, weldability, machinability, and surface finish for your customers extruded applications. Applications include transportation, architectural, consumer products and electrical. Silicon (Si) and magnesium (Mg) are the major alloying elements in this series due to the precipitation strengthening mechanism. Alberg has a unique offering for the 6xxx series extrusion billets, balancing the Si and Mg ratio which can give your customer a 25% extrusion speed increment while still meeting the AA chemical specifications. Interesting! On site support and 'boots on the ground' with your extruder, I'm sure you will be pleased with this performance. For more information, drop me a message. albertech@gmail.com

Safety effects all of us, not only in our chosen profession but also in our every day lives. We need to respect ourselves, our friends and colleagues, our clients / visitors, management and of course the place of work. We should be strong enough in character to STOP anyone from doing unsafe acts. This is our obligation not only to our colleagues but to their families and loved ones and we should expect the same. In 2021 recent reports have stated that there were 140 explosion incidents reported in the sector of Aluminium Production. This has continued a downward trend in reported incidents over the previous 4 years. In 2021, total incidents are lower than the historically high number of incidents (170 – 195) reported between 2016 and 2018! There were 116 Force 1 explosions, 23 Force 2 explosions and one Force 3 explosion reported in 2021. Compared to 2020, Force 2 explosions increased from 12 to 23, while the Force 1 explosions decreased from 134 to 116. One Force 3 incident has been reported each of the last three years. Sadly, these numbers look to be only the tip of the iceberg and it could be suggested that the reporting could be as low as only 5% of the actual number of incidents and accidents. Although this can not be confirmed. The major and avoidable risks in an aluminium casthouse are unquestionably the following. (1) Mobile equipment & coactivity. (2) Hot metal / burns. (3) Explosions (Force 1-3). Others exist and should also be addressed such as : Chemicals, Slips trips and falls, Hand / finger Injuries, Dust and fume and the maintenance activities of Working at height, confined spaces and hot works (Welding, burning, lancing etc). Many thanks for taking the time to read this blog, please feel free to share with your friends and colleagues. Alberg.tech has over 25 years experience in training and coaching safety in the casting environment with several presentations, videos and real life examples to share with your management and process operatives to increase their awareness and support a reduction in LTI's and 'god forbid' serious injury. Should you still require further help on this particular subject reach out and please contact : albergtech@gmail.com George

The annual Customer Satisfaction Survey (CSS), is a time proven critical feedback methodology to understand your customers and, if constructed correctly, what they actually think about your team, organization or the services your company can offer. From this feedback, you can formulate and implement corrective plans which will recover otherwise missed opportunities, reassuring your clients that you take their feedback seriously and further develop bonds and hopefully returning business. The Feedback from customers is one of the key requirements from your ISO9001 standard to demonstrate continual improvement within your Quality Management System (QMS). Sadly not all surveys are well received from the customer. They are often poorly constructed, repetitive, often sent at the wrong time or worse never seen to be acted upon year after year thus creating an often hidden from you 'what’s the point' internal response and therefore never returning a completed survey with what could have been missing valuable information. The survey method we at ALBERG employ is very different to the one I’m sure you have seen or used in the past. We consider representative 'real' important data and take samples from personal interviews with your key accounts. We ask relevant questions not for the sake but which add value to you and your customer. We focus on benchmarking and comparing your data with competitors and current market standards. We would also request that you perform a self assessment and reflect internally how you think you could do better with anonymous surveys taken in your own business environment. Finally we consider the price and the customers perception of value for money, after all that’s generally one critical requirement which brings your customer back year on year. Using our standard basic method you will see after some time how your business can actively 'listen' and corrects itself organically. The next CSS building on the previous one and so on with the results from feedback demonstrating this continous improvement path and growth. For more information contact us : albergtech@gmail.com

Whether in the casthouse or any other production process dependant part of your business, Quality Control is is something you must consider and dedicate the necessary time and resources to ensure specifications are met and moreover maintained to avoid variation in the customers product. A robust quality control system will ensure that your cast products comply with your customers specifications. A very good QC (will be abbreviated from now on) process will also demonstrate to your customers (and hopefully potential customers) that you have control and understand the capability of your facility which in turn will continually generate quality products, time after time, regardless of personnel, external conditions or process variation. Quality Assurance "All actions take to ensure that the standards and procedures are followed to and that the delivered products or services meet performance requirements". Quality Control "QC refers to the process most often implemented in manufacturing, of monitoring the quality of the finished products through a series of measurements and overall company commitment to making defect free products". I have visited many production sites and casthouses where understanding the benefit of QC is not fully recognised or adopted. Sometimes this entire process is seen as a 'headache' and unnecessary but in my experience its sorts out the Tier 1 suppliers from the rest, that's why the Automotive and Aerospace industry not only require these standards but demand that they are in place and well established before they will commit to production qualification trials. The measurement system to ensure conformity can be considered as a very basic block diagram, it really could not be simpler. We 'Measure' to 'Control' and compare the data, understand the process and any deviations with that we 'Improve', its a continuous closed loop and once we have enough data we can run statistical process control (SPC) to demonstrate 'Process Capability. More of this later... but for those savvy of CI you can see we are talking here about the building blocks to DMAIC. For the time being and for the sake of keeping this blog brief, we will consider only the casthouse process, and in particular the casting of slabs (for example). There are several 'Control Technologies' available to ensure your products conform to the customers specification and which will supply you the feed to perform our SPC charts. Hydrogen Measurement. Porosity and mechanical losses are well understood phenomena in aluminium casting and downstream failure modes. Therefore its a good idea to monitor the hydrogen levels in your liquid metal as close to the 'solidification process' as possible to avoid recontamination after the inline degassing sequence. There are a number of equipment's on the market today that can take inline H2 measurements. The measurement methods fall into two groups. A kind of solid vs liquid methodology. The first method which collect and measure the amount of gas extracted by heating a finite / known mass of alloy, sometimes this process is done under vacuum (Leco). The second method which use a tool to take real time measurements of hydrogen concentration in solution in the liquid (Alscan). We will consider the most popular here by use and elaborate on how they work, again there are many papers and OEM company literature on other systems that can perform exactly the same function so if your looking for such a device, take the time and look around for a system that meets your budget and requirements. I have attached for your convenience some data from the OEM's. Alscan One of the most popular systems sill in use today, with in the region of 300 units being deployed in most of the large aluminium casthouses. A simple to use process that provides accurate H2 readings. using Sieverts Law to determine dissolved H2 levels in the liquid aluminium. A new system that has been recently introduced is the Accurity system by Alsobia. Jasmin Proulx recently shared this information with me. I have attached the company literature below for your reference. If anyone is currently using this system I would love for you to get in touch. support@alberg.tech. Below we can see an I-MR Chart and a Process Capability chart. The data was taken over a rather large sampling rate for a customer that had a maximum H2 level in his specification of 0.20ml/100g Al. The data demonstrates the process is stable and repeatable with two red 'outliers' that could be explained to the customer if requested and not effecting the overall Cpk value which is >1. The control charts should be production line, product and alloy specific. Interestingly I created a H2 chart taking an average monthly hydrogen reading for a billet casting line in the Middle East. The hydrogen levels peak in the region due to the humidity and influence of the monsoon season in India. (June to September). Inclusion Measurement. Another data set generally required from the customer is the level of inclusions (inclusions being foreign particles not required in the product). I will follow up to this blog with another shortly on types of inclusions, their sources and how to eradicate at source. Several products exist to measure the level of inclusion in the melt. They differ slightly in their operation as some use samples while others are real time. The most commonly used methods are as follows: Below you can see two control charts made using PoDFA data taken on a slab casting line producing a lithographic alloy for a specific client. After several notable points were recorded and deeply investigated it was decided to use a Ceramic Foam Filter after the Deep Bed Filter to further enhance the molten metal quality. This demonstrates the benefit of 'Measuring' your product quality and taking proactive measure to correct the situation and no doubt reduce expensive customer complaints and possible claims. LiMCA N20 values for 3104 Can Body Stock alloys. The metal was extremely clean and inclusion free. The CpK value was >3. The sample size was also very good, over 200 measurements made. With this type of data it can be demonstrated to the customer that you operate a stable, benchmark world class casting centre and can reduce the sampling frequency, lowering operational costs freeing up process technicians and operators to work on other problems. Concluding While we have only really touch the tip of the iceberg in terms of Quality Control, there are many other aspects of the product that needs to be validated and controlled. such as physical geometry (length, width, thickness, diameter, sawn surface roughness to name a few). All of these parameters can be measured and analysed in a similar fashion to the metallurgical conditions. I would suggest that not at the same frequency as the variables effecting the product are not so fluctuating. The chemical side of the product is also a critical data set of course following the customers specification. (I did not mention this as this topic warrants a blog entirely on its own due to the process and details involved). Quality Monitoring : (Hydrogen and Inclusions) : Compliance of your products to the customer specs furthermore demonstrate the process capability to continuously generate quality products. Quality Control (SPC) : Use data! create control charts and establish process control limits, look at regular review, learn from the process and review the limits making them tighter whenever possible. By doing this you will improve your products and band reputation. Data exchange / Benchmarking : Establish internal specifications and if possible use external or customers laboratories (or even competitors such as Hydro BQA) to exchange results and benchmark data. Facilitate the exchange of best practices in metal treatment and process control. Many thanks for taking the time to read this blog, please feel free to share with your friends and colleagues. Should you still require further help on this particular subject reach out and please contact : albergtech@gmail.com George

A very interesting depiction of the mined in 2019 thanks to the British Geological Survey (2019) and the USCGS Mineral Commodity Summaries (2021). Many thanks for taking the time to read this blog, please feel free to share with your friends and colleagues. Should you still require further help on this particular subject reach out and please contact : albergtech@gmail.com George

Grain Refining : Ray Bignell Introduction In as cast aluminium, grains can be between 5 and 10mm in size and would give poor product performance. Examples of poor product performance are poor structures, porosity and analysis uniformity. Grain refining as the term suggests is achieved by adding very small amounts of TiBAl master alloy generally in the form of rod which reduces the size of the grains to a fraction of a mm. The benefits that a grain refining result in: 1. Increased Casting speed. Casting speed is generally in two steps, the speed at the start of the cast and at run or steady state. In technical terms casting speed is the heat input side of the heat balance equation and the water flow is the heat extraction, these levels set by the mould technology in question. With this in mind therefore the start speed is set at a safe level, to avoid bleed out and one where the start of the cast is crack free. The casting speed at the start is therefore set a high as possible to get a crack free butt and it has been proven that a grain refined ingot butt will allow higher start speeds than a non grain refined butt. The same is true for the casting speed in steady state where a grain refined structure will allow a higher cast speed than a non refined system. 2. More Uniform Structure Grain refined ingots will have a uniform structure throughout the ingot so from top to bottom and from core to edge will have grains that are very similar is size and shape. 3. Uniform deformation during downstream manufacturing Ingots with a uniform structure therefore will give uniform mechanical properties of the wrought products as ingot deformation and recrystalisation is improved during the hot rolling operation. 4. Uniform Chemistry A fine grain refined structure will give a uniform distribution of elements across the ingot and improved response during homogenisation. 5. Improved surface finish on sheet products A fine grained sheet, plate or extrusion will give good anodising response with no signs of steaks that can be associated with large columnar grains. 6. Improved porosity in plate products Hydrogen is ejected during solidification so bubbles are left at the grain boundaries so again a finer structure has more uniform porosity. Porosity is also known to influence tearing during hot rolling, 7. Heat Treatment response Linked to mechanical properties a fine grained sheet or any other wrought product will give an enhanced response when subjected to a thermal treatment. Such treatments could be an annealing cycle for soft alloys or solution treatment and precipitation treatment for heat treatable alloys. A non grain refined ingot or an interruption to a grain refiner supply will give what is known as a columnar structure. It is imperative that a fine equiaxed grain structure is obtained during the casting operation so that the ingot or billet produced can meet the wrought material specification that is required by end users. Grain refinement is required right at the start of the process and be interrupted throughout the casting process. Any interruption will give a columnar or most commonly referred to feathered or twinned structure. Solidification liberates heat so we would expect to see a plateau in the melt temperature time curve. In practice cooling below the equilibrium freezing point to required to nucleate the first dendrites. As dendrites grow heat is liberated and the temperature rises. The temperature drop required is termed as undercooling and is a measure on how difficult it is the nucleate the first dendrites. Typically grain refined alloys have very low undercooling compared to non grain refined alloys because the action of the grain refiner to bring on nucleation. Following the temperature rise it will fall again as heat is extracted. When casting the first solid nuclei are close to the mould wall. These start to grow and form an outer equiaxed zone. Dendrites growing parallel or opposite the heat flow advance more rapidly. Other dendrite orientations are overgrown due to mutual competition leading to the formation of a columnar zone. Beyond a certain stage in their development branches break off and become detached and grow independently and become equiaxed. Nucleation To undergo homogeneous nucleation large undercooling needs to be observed but never is this seen in practice as the alloys produced will be solid id we wait for the undercooling to take place! In the absence of undercooling a method to obtain homogeneous nucleation is where grain refiners are used which add sites for nucleation to take place. In this case solid particles of TiB2 or TiC form the grain refiner and other solid constituents will too serve as nucleation sites for grain growth. At the start of nucleation the structure is similar to the structure of aluminium. This process is known as lattice matching and whilst this is important for nucleation other contributing factors such as chemical effects, phases and segregations are known to assist. It is known that the more highly alloyed products for instance 2xxx and 7xxx are easier to grain refine than high purity versions. The mechanism of grain refinement is not a complex process and many theories have been put forward since the evolution of the technique back in the 1930’s. In all probably four or five grain refining methods have evolved but worth noting is that most of the theories have to rely upon particles to nucleate grains and whilst in detail each are slightly different they all appear to be similar to the operator on the shop floor. TiB2 Nucleants with Ti residual. This is where TiB2 particles act as substrates for TiAl3 which then nucleate alpha aluminium grains. TiB2 remain active and show no sign of fade and in time transform to (TiAl)B2. This can be regarded as the most popular of the methods to grain refine ingots. TiAl3 Nucleants. This is where undissolved TiAl3 acts as nucleant. These TiAl3 particles only survive about 1 to 2 minutes before complete dissolution. This method is generally used for surface critical applications. TiC Nucleants with residual Ti. This technique uses the same thinking as TiB2 nucleates but do not display agglomeration and are resistant to poisoning by Zirconium. Residual Ti with no intentional nucleants. Raising solute titanium to 0.05% to 0.08% will lower the partition coefficient low enough to bring on constitutional under cooling. Nucleation occurs from oxides, walls and junk in the alloy. Residual Ti only with no intentional nucleants. This is where we rely on adding sufficient to be in the peritectic region of the grain boundary and utilise the peritectic hulk theory where particles transform directly into the aluminium grain via the peritectic reaction. As most cast houses use TiB2 rod with solute Ti the mechanism of grain refinement can be explained and really embodies the current thinking offered by the experts in the field. Common grain refiners contain TiB2 and Al3Ti so probably the most accepted explanation is that a layer of TiAl3 has to be present on the TiB particle for to be capable of providing a nucleation site in alpha (FCC) aluminium. It is thought that the coating of the TiB particle occurs during the manufacturing of the grain refiner but the mechanism has yet to be explained. Grain refiners contain both TiAl3 and TiB2. It is known that TiAl3 particles measure 80 microns (a grain of salt is 80 microns) and they need about one minute to dissolve. TiB particles typically measure between 1 and 5 microns and require a certain number if discrete particles to generate grains that survive. This is where that grain refiner comes into play and is added in the form of AlTiB rod to the molten metal flow from the furnace. The rod addition rate is calculation is base on the number of discrete particles required not the Ti added form the rod itself. To explain nucleation particles are provided from the rod whereas the total titanium content arises from other inputs to the furnace. For all casting operations and the majority of alloys it is important to add titanium master alloy to the melt to maintain a surface layer on the TiB2 particles. The role of the Titanium, commonly known as solute titanium is required to obtain the surface layer on the TiB particles. It has been proved that 0.005% or 50ppm is sufficient for commercial alloys. To add titanium to a melt waffle plates containing Aluminium 6% or 10% Titanium are generally added to the furnace but other sources such as Aluminium 75% Ti compacts are now available. The titanium in the form of TiAl3 dissolves rapidly in the melt and can be measured when chemical analysis is carried out. The role of solute titanium is twofold. Firstly along with other alloying elements assists in the provision of nucleation sites and dendritic growth. Secondly these alloying elements exert a growth restriction effect called constitutional undercooling so give more opportunity for nucleation events. With this in mind therefore if the undercooling is large then nuclei are present in this area so further nucleation and growth of equiaxed grains can occur ahead of the columnar front. This process continues until a fine equiaxed structure is obtained. Growth restriction values m(k-1) can be estimated from phase equilibrium diagrams and from m (the slope of the liquidus) and k (solid composition divided by liquid composition). To confirm therefore that the role of titanium is twofold for nucleation and growth resistance. If grain refining is a problem, altering the liquidus slope to achieve undercooling is difficult in practice so increasing solute titanium in the furnace will increase growth restriction. The table summarises the effect of element concentration on the growth restriction and that titanium has a highly disproportional effect and 0.1% is equivalent to 4% silicon. Taking all of this into consideration the grain refining strategy for an individual alloy will depend on the alloy chemistry. In most cases TiB2 rod is added to the trough but the amount of titanium added to the furnace will depend on the growth restriction factor of the alloy. In general terms: Before the introduction of the in “launder rod addition” grain refinement was achieved by adding a 5%Ti 1% B waffle to the furnace. Typically between1kg – 1.5kg/tonne was the typical addition and whilst this gave fine equiaxed structures were obtained several operational problems arose. Such problems were that of “fade” whereby the grain refining efficiency decreased over time, agglomeration of TiB2 particles and poisoning of the grain refiner come to mind. The reason for the fade is that the TiB2 from the waffle agglomerated which forming a sludge which fell to the hearth of the furnace. Stirring the furnace partly regenerated the grain refiner but not to such a marked extent when compared with the efficiency following the initial waffle addition. Furnaces were generally static design so the stirring was normally performed after three hours but this in itself was not ideal as this would lead to the formation of spinels (hard oxides). Furnaces today generally are tilting design and therefore cleaner and with the TiB waffle addition now in the dim and distant past as grain refining technology improves fade is no longer an issue. The poisoning of grain refiners is well documented and in the main is a problem in alloys that contain zirconium. Whilst this does not affect the majority of the recipients of this presentation it is a real problem for the “hard” alloy producers. Zirconium is added to 7xxx series alloys to promote recrystalisation after hot rolling. Added as a 5% -10% Zr –Al master alloy the temperature of the furnace needs to be above 730°C to avoid zirconium aluminide, ZrAl3. This element is also very sludgy and blocks inline filters and mould distribution devices and in situations like this the drop has to be halted and remedial steps taken. Poisoning of the grain refiner was more of an issue with furnace waffle additions as the TiB was in the furnace and in contact with the elemental Zr in the metal. In such cases ZrB was formed rather than TiB2, this compound will not nucleate FCC aluminium. As the rod type grain refiners were introduced together with a furnace addition of titanium Zr poisoning is no longer reported as an issue. Chromium is too regarded as a possible candidate for poisoning but with the rod addition and solute Ti route and like zirconium is no longer reported. In silicon containing alloys, contents above 3% have the tendency to form TiS2 on the surface of the TiB2 so effecting the nucleation force of the boride particle so it is common to use a lot higher solute titanium levels in these group of alloys. βeta Aluminium in its purest form is very soft (poor growth conditions) and the earliest work suggested that alloying with other elements strengthen the alloy and in some cases the alloy can show strengthening by applying a thermal treatment. It has been previously discussed that these alloying elements assist in nucleation and to further this subject a measure of the constitutional effect for cellular to dendritic growth is known as β. This sums the total solute effect on the melt phase diagram: This simplifies the slope relationships between TL and TS in an alloyed system. The aluminium rich solid solution which solidifies first is known as alpha (α ) and the next to solidify is beta (β). If we consider the formation of a cast structure during initial solidification crystals begin to grow which contain an only a small amount of alloying element. During the process of further solidification the melt is enriched in the alloying element that steadily increases the alloy content of the crystal as it continues to grow. Many aluminium alloys suffer from hot tearing (cracking) during casting due to high thermal stresses developed during solidification. The type, size and morphology of intermetallics formed during the final stages of solidification can affect hot tearing tendency. Grain refiner additions, impurity levels and melt cleanliness have all recently been shown to individually affect secondary intermetallic phase selection in Al alloys. In turn, the type, size and morphology of such intermetallics can significantly affect the ability to carry out downstream processing and the mechanical properties of final components. In strong alloy the volume % secondary phase is known to have an effect on the fracture mechanics of the plate so too is the Fe bearing phase. The understanding of alloy is an entirely separate discussion but demonstrates the need to control the whole of the process for each from melting/alloying, grain refinement and casting and homogenisation. Common available commercial Al-Ti-B grain refiners in rod form are: Al-3-Ti-1B Al-5Ti-1B Al-3Ti-0.2B Al-5Ti-0.2B Al-10Ti-0.4 B For furnace titanium additions these are commercially available as: Al-6Ti Waffle Al-10Ti Waffle Al-70Ti Compact Used in the form of rod enables that additions are accurately controlled and by precise machine control, they do not fade and do not contaminate the furnace. Injection of rod is generally just after the furnace exit (but not at the spout) and against the flow from the furnace. Rod additions are always before inline devices so that adequate contact time can be allowed to allow complete dissolution. Just before the start it is quite common to lay an ingot or several feet of ALTiB rod so that any in line processes are grain refined and that the butt of the ingot is too grain refined. This not only helps to avoid start cracks but also means that the grain refinement process starts immediately. As we are a customer of the supplier of grain refiners the supplier must provide release data on the products supplied. His tests must show that the grain refiner is effective and free form coarse particles and oxides. It is also important that the correct chemistry is supplied and the rod diameter is correct. These products are very expensive and over grain refining products serves no purpose at all and could form AlTiB2 agglomerates which are detrimental to product quality. SEM of boride cluster showing alkali (K,P) peaks form source material with Ti and Al peaks. Worth noting is the O peak which indicates agglomerate probably formed around an oxide film. Grain refiner manufacturers have to routinely test their products to check for the efficiency, boride size and cleanliness. Such tests include: On line thermal analysis to check for undercooling. (Alu-Delta) Aluminium Association TP1 Alcoa Directional cold finger test. Certificates supplied with grain refiners should always contain this information. Trial for new suppliers materials or changes to their current rod should first be approved by the customer(s) effected from this this trial so any change in their downstream process can be linked to the trial, similarly if the trial aids and benefits. Also consult the changes through your respective technical - Quality - or change management group before full implementation is made. The above are results for the TP1 test ranging from 1 which is a columnar structure through to rating number 10 which is a fine equiaxed. Products with a number 10 rating are required for all applications. As mentioned previously grain refiners can create problems the most acclaimed if the premature blocking of filtration equipment as TiB2 clusters can combine with oxide films to form spinels which are large in size. It is also known that grain refiners can give fir tree structure in 1xxx and vertical folds in 5xxx alloys. This just supports both quality control and correct addition rates and certified machinery are required when rod refiners are being used. One alternative to AlTiB rod refiners are titanium carbon systems, these refiners were developed initially from “super6” rod refiners which contained very small amounts of carbon. This grain refiner contains both TiAl3 which is soluble and TiC which is insoluble and do not agglomerate like the TiB2 equivalent. They are known not to produce vertical folds in 5xxx and 1xxx can still exhibit fir tree. As TiC does not agglomerate this feature can be used to increase the life of filtration devices and in strong alloy can be used to have better control of grain size. Such are the issues with TiB grain refiners over time the use of TiC will increase. Conclusions To obtain a fine equiaxed structure a source of potent nuclei together with adequate growth restriction factor in the alloy. It is well proved that titanium added to the furnace is the best growth restrictor and should always be used no mater how small the addition is. Grain refiner rod used without solute titanium will not be as efficient as with. A grain refining strategy should be for each alloy group shall be devised and should be documented in SOP’s that should be adhered to. Remember grain refiners are expensive. Adding too much is detrimental to product quality and is a complete waste. Many thanks for taking the time to read this blog, please feel free to share with your friends and colleagues. Should you still require further help on this particular subject reach out and please contact : albergtech@gmail.com George