Aluminum alloy heat treatment technology

1. Principle of aluminum alloy heat treatment
Aluminum alloy casting heat treatment is to choose a certain heat treatment specification, control the heating rate rises to a corresponding temperature cooling, heat preservation time to must speed to change its alloy, its main purpose is to improve the alloy’s mechanical properties, enhance the corrosion resistance, can improve the processing, get the size stability.
2. Characteristics of aluminum alloy heat treatment
It is well known that for steel with high carbon content, the hardness is obtained immediately after quenching, while the plasticity is very low. However, for aluminum alloy, the strength and hardness did not rise immediately after the alloy was quenched, but the plasticity did not decline, but increased. However, after this quenching of the alloy, the strength and hardness of the alloy can be significantly improved after a period of time (e.g., 4-6 days and nights), while the plasticity is significantly reduced. The phenomenon of the strength and hardness of aluminum alloy after quenching is significantly increased with time. Aging can occur at room temperature, according to the natural aging, can also be higher than the room temperature at some stage in the temperature range (100 ~ 200 ℃), called artificial aging.

3. Principle of aging of aluminum alloy
Age hardening aluminium alloy is a complicated process, it not only depends on the alloy composition, the aging process, also depends on the alloy in the process of production caused by shrinkage defects, especially in space, the number and distribution of dislocation, etc. It is generally believed that the aging hardening is the result of the partial polymerization of the solute atoms.
When the aluminum alloy is heated, there is a vacancy in the alloy. In the quenching, it is “fixed” in the crystal because of the fast cooling. Most of the empty space in the supersaturated solid solution is bound to the solute atom. Because the oversaturated solid solution is in an unstable state, it is necessary to transition to the equilibrium state, the existence of empty space accelerates the diffusion velocity of the solute atoms, thus accelerating the partial polymerization of the solute atoms.
The size and number of hardened zones depend on quenching temperature and quenching cooling rate. The higher the quenching temperature, the larger the vacancy concentration, the more the hardening area and the decrease in the size of the hardening area. The higher the quenching cooling rate, the more space fixed in the solid solution, it will increase the number of hardening areas and reduce the size of the hardened zone.
A basic feature of precipitation hardening alloy system is changing with temperature and solid solubility of balance, namely with the temperature increasing solid solubility, most can be strengthening heat treatment of aluminium alloy are accord with the condition.