1. Billet annealing refers to the annealing before the first cold deformation during the pressure working process, the purpose is to obtain a balanced structure and a large plastic deformation ability of the billet. For example, the final rolling temperature of aluminum alloy hot-rolled slab is 280~330℃. After rapid cooling at room temperature, the phenomenon of work hardening cannot be completely eliminated. Especially for the heat-treated aluminum alloys, after rapid cooling, the recrystallization process cannot be completed, and the supersaturated solid solution cannot be completely decomposed in time, and still retains a part of the work hardening and quenching effects. It is difficult to continue cold rolling of china 6A02 aluminum plate without annealing. Therefore, slab annealing is required.

2. Industrial pure aluminum and low-alloyed china 6A02 aluminum plate have higher plasticity, and can be directly cold worked without billet annealing. After annealing and heat preservation, the aluminum alloy plate that is not strengthened by heat treatment can be directly cooled in the air; for the aluminum alloy plate strengthened by heat treatment, it should be cooled at a specified speed. For the annealed aluminum sheets in stacks, they can also be released from the furnace after being kept warm, and covered with asbestos cloth for slow cooling. In actual production, slow cooling can also be carried out by means of downturning the furnace. For example, after annealing and heat preservation of 7A04 alloy at 400~420℃, it is directly transferred to a low temperature furnace with a preheating temperature of 230℃. After heat preservation for 3 hours, it is air-cooled, and the same structure and properties as the slow cooling effect can also be obtained.

3. The billet annealing can be heated in an air circulation resistance furnace, or a fuel furnace such as heavy oil or liquefied petroleum gas can be used for heating. In recent years, a new process of "medium temperature rolling" has been adopted in the production of china 6A02 aluminum plate, that is, after the hot-rolled slab is cooled to 100~250 ℃, it is directly sent to the cold rolling mill for rolling, without annealing the billet.