3A21 aluminum plate is an Al-Mn alloy, and 3A21 aluminum plate is the most widely used type of rust resistant aluminum. Its strength is not high (only slightly higher than industrial pure aluminum) and cannot be strengthened by heat treatment. Therefore, cold working methods are often used to improve its mechanical properties; It has high plasticity in the annealed state, good plasticity in semi cold work hardening, low plasticity in cold work hardening, good corrosion resistance, good weldability, and poor machinability.