Aluminum alloy annealing process and billet annealing

In the process of cold deformation, in addition to the changes in shape and size, the internal structure of aluminum alloy also changes. Under the action of external force, the grains inside the aluminum alloy are forced to slip, rotate and break, the shape of the grains changes, the grain boundaries stretch along the deformation direction, the grains break, and are pulled into fibers. In this way, the equiaxed grains with different orientations gradually develop in the same direction, forming a deformation mechanism. This result makes the metal anisotropic. At the same time, due to work hardening, the strength of the metal increases, the plasticity decreases, and the ability to continue to withstand cold plastic deformation is gradually lost.
If the aluminum alloy after cold deformation is heated, as the heating temperature increases, the atomic activity inside the aluminum alloy increases sharply.
The aluminum alloy will be heated to a certain specified temperature, kept warm for a certain period of time, and then slowly cooled to room temperature. Through the thermal motion of atoms, the internal structure of the metal changes, the internal stress is eliminated, the strength is reduced, and the plasticity is increased, so that the aluminum alloy can withstand cold processing deformation. This heat treatment process is annealing.

Annealing of
hot-rolled aluminum sheet billets generally requires billet annealing before cold rolling, because the final temperature of hot rolling is generally between 280 ℃ and 330 ℃ , and it is quickly cooled to room temperature in the air. In this case, local work hardening is maintained in the hot-rolled slab. If the work hardening is not completely eliminated by annealing, it is difficult to continue cold rolling, so billet annealing is required.
For pure aluminum and 3003 aluminum alloy, their plasticity is relatively high, and billet annealing can be performed directly after hot rolling.
For aluminum alloys that cannot be heat-treated and strengthened, they can be directly cooled in the air after annealing and heat preservation.
However, for aluminum alloys that can be heat-treated and strengthened, they should be slowly cooled at the prescribed speed after annealing and heat preservation, so that the strengthening phase in the aluminum alloy can be fully resolved during the cooling process to prevent local quenching caused by too fast cooling.
When selecting the annealing temperature and heat preservation time for aluminum-clad plates, the copper diffusion problem in the aluminum-clad layer must be considered.
If the annealing temperature is too high or the holding time is too long, the copper atoms in the aluminum alloy will diffuse into the surface aluminum layer, thereby reducing the corrosion resistance of the aluminum plate.