Extrusion Billet : Assessing your standards.

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.

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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

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