Is it possible to forge aluminum as one would forge iron or steel?
I was wondering what would happen if civilisation collapsed and hand blacksmithing became common again, with people plundering the remains of the cities for raw materials. Would they be able to use the aluminum they found? I know that aluminum was a rare semi-precious metal until the late 1800s, when a method was developed to extract it by the use of enormous quantities of electricity… so there was no medieval trasdion of aluminum-smithing. But if aluminum had been available earlier, could hand smiths have worked it?
Aluminum can also extruded by forcing a billed through a die. Aluminum cans are produced by smacking a disk of soft aluminum which flows almost like water into the space between the mandrel and the die.
As others have noted, aluminum certainly can be forged. However, it is not a good replacement for steel in most applications; one cannot obtain the hardness and toughness that one can with steel, hence, you see no aluminum knives. Aluminum, although fairly resistant to environmental corrosion, is also highly reactive with some types of acids. Aluminum also suffers from continuous creep and (minor) plastic deformation at even small loads; hence, it is not typically used for structural applications like buildings and bridges, although this is probably not an issue with your post-apocalyptic situation.
Another thing to take into account is how sensitive the structural/mechanical properties of aluminum are to alloying elements and heat treatment; even small variations can turn a piece of aluminum from being strong and tough to being brittle and crack prone. Iron and steel (predominantly iron-based alloys) are much more tolerant, and while they may be more difficult to handle and form, allow much greater flexability in application; indeed, aluminum is typically used not for greater strength or cost but because of it’s lighter weight, formability in thin wall sections, and corrosion resistance.
Aluminum is a great material in its venue–for lightweight aircraft parts, corrosion resistant scuba tanks, thin wall beverage cans, et cetera–but no replacement for steel when it comes to tools, threaded fasteners, structural members, wire rope, et cetera.
I would think that if creep were a problem at ordinary temperatures, the wings of an aircraft would gradually become concave upward with time. In most flight regimes the force on the wings is always in the same direction.
True, but creep is actually a consideration with regard to high performance aircraft. Inconel, titanium alloys, and other superalloy metals are often used in critical areas where creep may be a concern. Depending on treatment and alloying elements, aluminum can also age-harden, and if it becomes cracked it can locally harden (due to work) which may contribute to further fracture propagation. Aluminum is not a particuarly robust material in fatigue loading, either, again owing to its deformation characteristics. And depending on how it is formed it can be very anisentropic (material properties differ in direction). Steel is somewhat less sensitive in that manner and is easier to treat and modify, especially if you don’t have tight process control. On the other hand, for some applications requiring corrosion resistance, light weight, high thermal emissivity, or certain nuclear interaction properties, aluminum is the bomb. But as a general structural and tool material, not so great.
Just to clarify, you can’t ‘work’ aluminum like you can steel. That is, you can’t heat up a part of it and hammer it into shape like steel/iron. Aluminum won’t ‘spot’ heat, its too good a conductor. Same way you can’t cut aluminum with an oxy/acytelene torch or weld it with a standard electric arc welder.
Steel is fairly easy to forge because it goes from solid to liquid gradually as it heats. Steel starts to soften long before it actually goes liquid, so a blacksmith can maintain a piece of steel at a temperature where it’s soft enough to form yet still stiff enough to hold its shape.
Aluminum tends to go from hard to liquid much more quickly; the temperature range where it’s softened enough to form yet still stiff enough to hold that form is much smaller, and a smith trying to hammer hot aluminum into shape is going to have to be very careful or he’ll end up turning his workpiece into a puddle. With aluminum, if you want a complex shape, it’s usually much easier to cast it in a mold rather than try to forge it. It’s not impossible to forge aluminum, but much trickier without precise temperature control.
Ah, thank you, Hail Ants and AndrewL. This is the kind of answer I was looking for: about hand forging. Not that I don’t appreciate the other replies either. I didn’t know that aluminum was so sensitive to differences in alloy compared to iron and steel, either. Thanks!
I should also point out that casting aluminum is fairly easy to do, something that any decently competent smith could figure out. So in the scenario proposed in the OP it’s entierly possible that people could take scrap aluminum and recast it into new forms. But the resulting casts wouldn’t be as strong as the original aluminum, due to being a mixture of different random alloys and contaminants, and over the years as the aluminum was repeately recycled the quality of the material would get worse and worse. You might well end up with a material only useable for decorative purposes.
If you were a medieval smith with a stack of aluminum ingots, what would you make out of them? Would there be any sort of weapon or armor they would be superior to steel for? Aluminum swords are out, but what about aluminum helmets and breastplates? Arrowheads? How about the pole element in a polearm…you might want a steel spearhead, but how about an aluminum shaft rather than a wood one?
Aluminum isn’t really hard or tough enough to be used as any kind of arrow or spear point, nor as armor. You could make a shaft of it, but it wouldn’t be of any great benefit; wood is stronger than steel, not to mention aluminum, per weight.
And you wouldn’t want to put aluminum and steel in direct contact–like a steel head on an aluminum shaft–for obvious reasons.
Interesting. I’ll note, under their Vehicles section, though, that they list one aluminum-fabricated vehicle with which I am familiar that is widely (and rightly) disparaged for its lack of durability in normal operation.
I suppose the designers do the best they can to meet an operational requirement that emphasises a low vehicle weight.
I’m not sure why the British used aluminum superstructure on warships. I suspect it was in order to cut down weight aloft. Modern warsips like destroyers are so loaded with armaments and radar and sonar and on and on that they are top heavy. In any case during the Falklands war I believe that some of the aluminum structure actually caught fire.