what does annealing do to aluminium?

Question

can it be used to increase strength somehow?... perhaps when coupled with another treatment/process?

Answer 1

This is two complex insight questions in one.

In general annealing improves ductility of a crystalline material. It does so by reducing the internal stress and rearranging the atoms to a more orderly packing while getting rid of dislocations. In special cases, such as with iron, annealing also changes the lattice structure. Annealing may increase or decrease the hardness of a material: It is incorrect to make a general statement either way. The hardness may increase or decrease depending on whether the more orderly bonds are stronger or weaker than the dislocation bonds. For example, a perfectly annealed carbon lattice, a diamond, has a much better hardness than coal because the perfectly covalently bonded carbon lattice is stronger than a disorderly bonded. In contrast, annealing makes the quenched-in hard (gamma) iron (a paramagnetic: not attracted by a magnet, exists at equilibrium only at above the Fe Curie temperature) to become the softer (alpha) iron (a ferromagnetic: attracted strongly by a magnet).

For aluminum, depending on how badly it was cold-worked, annealing may make it more ductile and slightly softer due to the lowering of atom-dislocation percentage. Aluminum solid, unlike iron, exists in only one face-centered cubic phase (think of a cube with one Al atom at each corner and one at each center of each face). So annealing cannot change the phase of aluminum to soften the hardness like it does to iron.

To make aluminum harder, materials engineers use similar atomic-scale plastic-flow barriers trick applied to carbon steel. Carbon steel (iron with less than 2% carbon) when quenched latches carbon atoms into interstitial voids of the gamma iron’s face-centered cubic lattice (a relatively loosely packed lattice). The resultant crystal becomes harder because some of the iron atoms are wedged and require stronger forces to flow on one another. Unlike iron, aluminum inter-atomic distances, unfortunately, are too short for carbon atoms to fit into the face-centered cubic interstitial voids. Hence metallurgists of the earlier centuries cannot harden aluminum the way they did to carbon steel. As metallurgy science gets smarter, however, instead of interstitial wedging, metallurgists started thinking about “replacement wedging”: Copper atoms, slightly larger than aluminum atoms, when dispersed into the aluminum lattice to replace the aluminum positions at an elevated temperature and suddenly quenched will make the alloy structure strained and hence harder to flow plastically. Several refinements of this fundamental replacement-wedge alloying and heat treatment techniques, called precipitation hardening or dispersion hardening, have made a family of “duralumin,” aluminum-copper with other minority wetting elements, alloys used as combustion-engine pistons, aircraft frames, etc...

Answer 2

Annealing Aluminium

Answer 3

It's basically a process of heating and slow cooling to strengthen the aluminum and reduce brittleness.
It's not just for aluminum, it's a common process used on other metals, plastics and composites.
There are many companies which offer this as their exclusive service so that a metal or plastics manufacturer can simply "out-source" his product for the annealing operation and save revenue on the cost of buying expensive annealing equipment as well as the added cost of labor and maintenance that would go with it.

Answer 4

Simple sample.... take a small sheet of aluminium, let it hang, tap it....it may well ring...its work hardened. Try to bend it a couple of times, it will start to crack. In other words, the structure of the metal is under stress. When it is annealed, it will bend easily, bear in mind that the action of bending will work harden the metal.
To anneal aluminium, smear ordinary bar soap over the area, heat with blowlamp, when soap is brown, stop heating....job done

Answer 5

This Site Might Help You.

RE:
what does annealing do to aluminium?
can it be used to increase strength somehow?... perhaps when coupled with another treatment/process?

Answer 6

After a certain amount of working (bending) it gets work hardened, so you anneal it to make it softer and regain its malleability again before working it further, there are many types of Aluminium, some more suitable to bending than others

Answer 7

It is used to soften and make it more malleable whilst retaining it's strength. That allows it to withstand shock and vibration much better.

Some aluminium alloys such as duralumin (aluminium,, copper, silicon, magnesium and manganese) are annealed to make them more malleable for shaping and then when hammered they harden back to a more rigid strength.

Answer 8

As a welder and metal worker for years, you come to realise that metal has a what I call a grain and a cell structure, it is easier to think of it like this.
when metal is poured from the furnace it cools at a regular rate and has an even structure.
When you start to work it by rolling , bending and forming stresses form the grain structure is distorted, this resulted during the war with liberty ships, welded plate steel ships tearing themselves apart at sea, down the heat affected zone.
we often call metal that has built up stress like that 'work hardened' it can be relieved by careful and even heating to re-form the even structure before further forming of welding can be carried out. For those interested in Aluminium oxidisation look up Thermite Welding and how to oxy-acetylene weld it.

Answer 9

annealing is a process of heating and cooling gradually to improve the flexibility of alumininium... but the main problem is the plasticity of the metal... steel for instance gets hot, goes red, and melts aropund 3200c ally goes plastic, and falls apart at just over 800c with no warning whatsoever

we anneal copper, its as good as new, we anneal steel, manipulate it and reharden it afterwards... ally doesnt let you do that, it becomes brittle and snaps along the stress points or folds...

thinner ally bends easily, thicker stuff needs to be cut and welded, or it will fracture... even riveting doesnt cure the stress fractures...

on every aeroplane ever made theres a man whose job it is to check for missing rivets.... riveted fabrications like airframes and wings are designed to flex, welded structures arent...

flexion leads to cracking...

oh, i made radio dishes for the MOD...

Answer 10

John Cob is correct except for one important factor, the aluminium will re-vert back to normal very rapidly after this operation, I have worked with it in aircraft construction and the aluminium mentioned earlier containing copper" "duralimin" which is very hard cannot be welded or heated excessively without destroying its stated properties, thus it is then no longer "duralimin"