New application of aluminium alloy
Owing to the fact that the subject material of this article is, in itself, fairly unremarkable, we should, perhaps, consider what it is that makes a material advanced. Is it significant that it is of an unusual composition? Perhaps we consider a material to be advanced if it has unusual or desirable properties. Possibly a combination of criteria make a material seem advanced to us. An interpretation which I would like to use, for the purposes of this article at least, and perhaps for other articles to follow is that a material is an advanced one if it offers us new opportunities in design.
We might consider a mundane polymer not to be an advanced material. If we take two thin sheets of it, and separate these with a honeycomb structure, we create something very stiff and lightweight. Some may consider this to be advanced; however, others would correctly point out that much better materials of the same type are available. However, by special processing, we can fill the void in between the two sheets with a hard foam of the same material. Again we have a stiff, lightweight structure, but without the complication of manufacturing a honeycomb structure and without the risk of delamination of the skins from the honeycomb. Bonding to polymers is often problematic and therefore risky and so we might well contend that this new structure, made entirely from a mundane polymer is an advanced material, as it offers us new possibilities in design. Such materials don't find use in racing engines, and probably not in racing cars, although they have existed for many years.
I would certainly consider the material to be advanced in the above-mentioned state, and it is on this basis that I propose the equally mundane aluminium alloy AlSi10Mg to be advanced. Owing purely to the fact that it is, currently, one of the only available aluminium alloys capable of being processed successfully by 'direct' rapid prototyping methods, it offers unique opportunities to us. The material itself, in terms of composition is not a new one, nor is it remarkable in terms of its mechanical or physical properties. Possibly it has been chosen for this application owing to the fact that it is available as a 'master' casting alloy and so will contain extremely low levels of impurities.
The process itself uses very finely divided 'powdered' material which is fused together to form a complete part by the use of lasers. The quality of the powder is critical to the success of the process, which has only recently been available. I was fortunate enough to have some parts made by the same process in the USA a few years ago, but the material lacked density, was extremely weak and the metallurgical structure, even in areas of the part with reasonably density was not far short of abysmal. However, the new process offers a good level of strength, commensurate with that which we might expect from a casting in the same material. We are now, however, bound only by our imagination and knowledge of how the process works in designing parts which were, hitherto, impossible to make, as shown by the accompanying picture. This complex part is made as a single component.
Fig. 1 - This complex aerospace part is made as a single component.
Written by Wayne Ward