The heat treatment of aluminum alloy rods is to select a heat treatment specification, control the heating speed up to a certain temperature to hold the heat for a certain time and cooling at a certain speed, change the structure of the alloy, its main purpose is to improve the mechanical properties of the alloy, enhance the corrosion resistance, improve the processing energy, obtain dimensional stability.

As is known to all, for steels with high carbon content, high hardness and low ductility are obtained immediately after quenching. However, it is not the same for aluminum alloy rod. After quenching, the strength and hardness of aluminum alloy rod do not increase immediately, and the plasticity does not decrease, but increases. But this quenched alloy, placed for a period of time, the strength and hardness will be significantly improved, while the plasticity is significantly reduced. After quenching, the strength and hardness of aluminum alloy increase significantly with the growth of time, known as aging. Aging can occur at room temperature, which is called natural aging, or it can occur at a certain temperature range above room temperature, which is called artificial aging.

Aging hardening of aluminum alloy is a very complicated process, which not only depends on the composition of the alloy, aging technology, but also depends on the defects caused by the shrinkage of the alloy in the production process, especially the number and distribution of vacancy and dislocation. It is generally believed that aging hardening is the result of solute atom segregation forming hardening region.

When aluminum alloy rods are heated during quenching, vacancies are formed in the alloy, which are "fixed" in the crystal without time to move out due to the rapid cooling during quenching. Most of these vacancies in susaturated solid solutions are bound to solute atoms. Because the supersaturated solid solution is in an unstable state, it must transition to an equilibrium state. The existence of vacancy accelerates the dispersion rate of solute atoms, and thus accelerates the segregation of solute atoms.

The size and number of hardening zones depend on quenching temperature and quenching cooling rate. The higher the quenching temperature is, the larger the vacancy degree is, the more the hardened zone is, and the smaller the size of the hardened zone is. The larger the quenching cooling rate is, the more vacancies fixed in the solid solution, which is conducive to increasing the number of hardening zones and reducing the size of hardening zones.

One of the basic characteristics of precipitation-hardened alloy systems is the equilibrium solid solubility which varies with temperature, that is, the solid solubility increases with temperature. Most aluminum alloys which can be strengthened by heat treatment meet this condition. The solubility-temperature relationship required by precipitation hardening can be explained by A1-4Cu alloy of aluminium-copper series