1. The principle of heat treatment of aluminum alloy

The heat treatment of aluminum alloy castings is to select a certain heat treatment specification, control the heating rate to rise to a corresponding temperature, hold for a certain period of time, and cool at a certain rate to change the structure of the alloy. The main purpose is to improve the mechanical properties of the alloy and enhance corrosion resistance. performance, improve processing performance, and obtain dimensional stability.

2. Characteristics of aluminum alloy heat treatment

It is well known that for steels with higher carbon content, high hardness is obtained immediately after quenching, while ductility is very low. However, this is not the case for aluminum alloys. After the aluminum alloy is quenched, the strength and hardness do not increase immediately. As for the plasticity, not only does not decrease, but it increases. However, after this quenched alloy is placed for a period of time (such as 4 to 6 days and nights), the strength and hardness will be significantly improved, while the plasticity will be significantly reduced. The phenomenon that the strength and hardness of aluminum alloy after quenching increase significantly with time is called aging. Aging can occur at room temperature, which is called natural aging, or it can occur in a certain temperature range (such as 100-200 ℃) higher than room temperature, which is called artificial aging.

3. Principle of aging strengthening of aluminum alloy

Age hardening of aluminum alloys is a rather complicated process, which not only depends on the composition and aging process of the alloy, but also on the defects caused by the shrinkage of the alloy during the production process, especially the number and distribution of vacancies and dislocations. It is generally believed that age hardening is the result of the segregation of solute atoms to form a hardened zone.

When the aluminum alloy is quenched and heated, vacancies are formed in the alloy. During quenching, due to the fast cooling, these vacancies are "fixed" in the crystal before they can be removed in time. These vacancies in supersaturated solid solutions are mostly bound to solute atoms. Since the supersaturated solid solution is in an unstable state, it must transition to an equilibrium state. The existence of vacancies accelerates the diffusion rate of solute atoms and thus accelerates the segregation of solute atoms.

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