Additive manufacturing of an ultrastrong, deformable aluminum alloy
nature.com
nature.com
WWII-vintage Japanese duralumin (Al-7075) is nearly as strong (~600MPa), and very ductile. It's also nearly 100 years old.
I guess the innovation here is that they're making this alloy with additive manufacturing techniques? It's not that noteworthy, IMO. It would be jaw-dropping if it were a 1000MPa alloy -- that's like the Holy Grail for aluminum -- but they're still far from that mark.
"Light-weight, high-strength, aluminum (Al) alloys have widespread industrial applications. However, most commercially available high-strength Al alloys, like AA 7075, are not suitable for additive manufacturing due to their high susceptibility to solidification cracking."
"the Innovation" is that high strength alloys like 2xxx and 7xxx are notorious for their "unweldable" nature.
So to report a fairly rigorous investigation of such a material being successfully processed via PBF is interesting.
There are essentially 3 ways to do it, different composition, grain refiner, or pulse shaping.
They seem to be targetting some combo of the first two.
The work is complete, but also very early..(limited macro mechanical work)
small scale mech props work can be very very different than practical size structures like a E8 coupon or fatigue test artifacts
The other issue is that creating new alloys is largely academic.. as the as qualification and supply chain constraints in most performance driven industries with any real market make it a non-starter
Not to say it's not interesting though, I'm excited to see where they take the work next!
Sounds expensive.
How do we arrive at that kind of alloy? (If it was explained in the paper, I didn't understand it)
The paper has links for other work with all kinds of similarity.
Apologies for the poorly phrased comment.
That’s why this laser sinterable superalloy is really interesting.
But the field is developing rapidly and we are already talking about complex concentrated superalloys. There are spectacular advances happening right now at every level of alloy development. The fact that additive manufacturing is far out of equilibrium is a problem for now, but this could become an advantage instead with the right alloys.
Steels can be very complex as well.
SS 904L: Nickel, Chromium, Carbon, Copper, Molybdenum, Manganese, Silicon, Iron
Tool steel alloys (used for machine tools, hand tools, knives, etc) have iron, carbon, tungsten, chromium, vanadium and molybdenum.
Carbon steel is the most basic alloy steel, it consists of iron and carbon (and impurities).
Pure metals are soft, because all their atoms have the same size, so the atom layers can slide over the others.
Mixing metals with different sizes increases the strength, because now the atom layers are no longer smooth, but they have bumps, which prevent sliding.
It can be shown that mixing many different kinds of atoms, taking from each about the same quantity, can provide very good mechanical properties, because the bumps in the atom layer will be frequent and they will have varied sizes and a random distribution, which will prevent any alignment between bumps, which could facilitate the sliding of the layers. Think about how to design an anti-sliding shoe sole. Random bumps of random size would give the best result.
The so-called "high entropy" alloys contain at least 5 different metals, with about the same quantity from each.
However the alloys that contain almost equal quantities of each component are very expensive. In order to make a cheap alloy, one must have one or at most two components in a much larger quantity than the others, so that the abundant components can be chosen from the few cheap metals, e.g. iron, manganese or aluminum, while the other components, which are added in small quantities, can be chosen from expensive metals, like nickel and cobalt.
For this reason, the better "high-entropy" alloys are normally replaced by the cheaper "medium-entropy" alloys, which use 5 metals, like the "high-entropy", but which are used in quite different quantities, with larger quantities from the cheaper metals, if possible.
The use of "high-entropy" alloys and "medium-entropy" alloys has begun only relatively recently. They are used to replace the cheaper classic alloys only when they offer a decisive advantage that can justify their higher cost.
This case is one such example. From the classic aluminum alloys, some of the weaker alloys, like AlSi or AlMgSi can be easily 3D printed, but they have low strength. The classic high-strength aluminum alloys cannot be 3D printed. Therefore this was a clear case when a newer kind of alloy must be tried, if high strength is desired. They have experimented with certain kinds of medium-entropy aluminum alloys, to keep the cost acceptable (and also in this case the high content of aluminum keeps the density low and the conductivity high, which are frequently the reasons for choosing an aluminum alloy), and the results were good.
Nevertheless, this alloy is likely to be several times more expensive than AlSi or AlMgSi, so it will be used only when its high strength is necessary.
The phase diagrams for these types of alloys look wild (you often want to achieve a certain material phase during cooling to "lock" in to get certain characteristics), and it can be difficult to ensure that the smaller metals participate during cooling. Also difficult to dissipate these slightly during tempering, typically to increase ductility.
This is probably why 3d printing hasn't been done in earnest, you can't design something within tight tolerances with unknown material properties.
https://www.renishaw.com/en/metal-3d-printing--32084
https://www.trumpf.com/en_US/products/machines-systems/addit...
Aluminum is already incredibly energy intense to refine - 190-230 MJ/kg. [https://energyeducation.ca/encyclopedia/Aluminum#:~:text=The....]
This isn’t even making a dent.
The vast majority of alloys can be recycled by just melting them down and separating the elements.
The ratio of Al to the other components is over 10:1 so as long as the intermetallics can be separated, they don’t even need to be recycled, just slagged off (then sent to a more specialized recycler)
If we assume that it is possible, then for Al92Ti2Fe2Co2Ni2 the waste would be Fe2Al6 + Ti2Al6 + Co2Al9 + Ni2Al6, so 27 of your 92 Al would be tied up in the waste. It’s a rough estimate and there are some caveats (I did not bother looking at ternary or quaternary intermetallics, or the miscibility of the binary ones, for example).
A more realistic scenario would be to dilute that with pure Al to get some lower-grade Al alloy, rather than recycling it directly into pure Al or very specific, very complex alloy.
Yes, please :-)
# caveats
This is just my feeling. I looked only at the binary phase diagrams, in reality there could be ternary or quaternary compounds. The article mentions that the alloy is an Al-rich matrix with the other elements in small crystals within it, with different structures and compositions. So the picture is quite complicated. To get a definitive answer, someone would need to do a proper study. I am not saying that it is impossible, just that it sounds very hard. That said, there could very well be other ways that escape me at the moment. I am happy to investigate further for a fee :)
# Fe-Al, looking at the phase diagram here [1]
There is a tiny temperature range (between around 650 and 660 °C) in which solid Al coexists with liquid Fe-Al. So in theory the mixture could be heated until it is all molten, then cooled slightly to precipitate Al, which could then be taken out, leaving Fe-enriched liquid. It seems feasible but impractical (temperature control would need to be absolutely spot on, and other elements would probably change the picture a bit).
# Ti-Al, phase diagram here [2]
There is a temperature range in which Al-rich liquid coexists with solid TiAl3. That solid could be removed, leaving a liquid that is mostly Al but still has significant Ti impurities.
# Co-Al, phase diagram here [3]
This one is similar to Ti-Al, except that Co is more soluble in liquid Al than Ti is, so there would be more Co impurities after taking out the Co2Al9 solid. The temperature range is also much narrower (650°C-700°C, eyeballing the diagram).
# Ni-Al, phase diagram here [4]
It’s worse than the others, because Ni is soluble even in solid Al. Also, melting is almost congruent, meaning that all the solid would melt at the same time, there is no coexistence of a liquid and a solid phase. This prevents from trapping the impurities in a solid to purify the liquid or the other way around. I don’t really see a way with this one.
# magnetism
Using magnetism was mentioned in the thread. I don’t think it would help. At high temperature, all these elements are paramagnetic. Some of them (Fe, Ni and Co) have a larger magnetic moment and would be more strongly attracted in a magnetic field than Al and Ti, but I don’t think it would be sufficient to really separate them (all of them are in minority compared to Al). And Al and Ti are not that different from a magnetic point of view and i don’t see them being separated by a magnetic field.
# oxidation
It is not inconceivable to inject oxygen to try to trap some elements in oxides that have typically much higher melting points than the metals, which would help with the narrow temperature ranges. These metals can form spinel compounds, at least TiFe2O4, NiFe2O4, and many more. One problem is that Al2O3 is also very stable (which is why it is very costly to get aluminium metal from aluminium ore. There are also aluminate compounds such as FeAl2O4. Figuring out which one is more stable and whether it could be feasible is quite a bit of work in itself.
[1] https://www.researchgate.net/profile/Qingyou-Han/publication...
[2] https://www.researchgate.net/publication/325471220/figure/fi...
[3] https://www.mdpi.com/materials/materials-13-03152/article_de...
[4] https://www.researchgate.net/profile/Matthew-Weeks-3/publica...
If you were tasked with recycling this metal, what order of operations do you think would work best to extract the most usable raw metals out?
Are there techniques to combine these phase diagrams to figure out multiple interactions? I’m guessing the minor components also have their own two phase regions that mess things up
This shows that Al with some Fe is in 2 phases when it is solid (pure Al on one side and FeAl3 on the other). However, above 660.452°C, there is only one liquid and Al and Fe cannot be separated. There is a tiny temperature range where there is a combination of liquid Al and solid FeAl3, between 655°C and 660.452°C, so completely impractical from an industrial point of view.
That’s an example; it’s even worse with Al and Ni because even the solid is a mixture. I am less familiar with the Al-Co and Al-Ti phase diagrams, but looking at them Al-Co seems similar to Al-Ni and Al-Ti to Al-Fe. Multi-elements alloys would be a bit different but not too much: if everything is soluble in Al separately, then all of them at once are also soluble to some extent.
In short, it might be possible to extract pure Al for recycling, but it does not seem to be easy and there would still be a lot of Al bound to the other metals in the waste.
It's where it gets mixed up with other 'waste', that complicates things.
Separating alloys it's often much harder because alloy component tend to change phase together (so you can make them liquid, but you still have no way to separate when they are liquid) chemical bonds keeps them together. For some it's easy, let's say you add a substance that separate them, or heat separate them because they change from solid to liquid at different temperatures and so on, for many others it's complicated enough you recover little quantity of the original material spending too much in the process.
To you, maybe. Not to everyone. Different people have different priorities.
If there was one single most important issue, we could all agree to use the single best alloy and be done with it.
Steel so far it's not because to make new steel out of scrap metal we need coke, there are various experiments to recover steel only adding energy but so far nothing on scale so while recyclable formally (and VERY recycled) it's not circular.
Due to volumes and natural resource limits anything we can do ad infinitum is a godsend because we know if we are able to produce and recycle enough we will never be short of it. That's why it's definitively a general priority. We have started to understand that anything we do on scale we also must count how to dispose of it and how much resources we consume in the process, the era of abundance enough not to care is largely ended and the outcome is hard enough to learn the lesson.
And I give that answer while purposefully ignoring how much aluminum there is in the world.
Yes, aluminum is abundant, BUT we already have witnessed scarcity issues in the supply chain, mostly due to poor diversification combined with geopolitical issues, but anyway scarcity. Since smelting and scrapping aluminum it's roughly easy recyclability is important because it can be "domestic" easily, like the one of glass.
Try to see the big picture, not the detail, meaning the complexity of current state of things and the fragility such complexity imply in a world heating toward a III worlds war.