On 2018-08-08 14:48:54
Aluminum alloy heat treatment characteristics and principle
1. Principle of aluminum alloy heat treatment
The heat treatment of aluminum alloy castings is to select a certain heat treatment specification, control the heating speed to a certain corresponding temperature under a certain period of time with a certain rate of cooling, change the structure of its alloy, its main purpose is to improve the mechanical properties of the alloy, enhance the corrosion resistance, improve the processing energy, to obtain the size of the stability.
2. Characteristics of aluminum alloy heat treatment
It is well known that for steels with a higher carbon content, high hardness and low plasticity are obtained immediately after quenching. However, aluminum alloy is not, aluminum alloy just quenching, the strength and hardness is not immediately increased, as far as plasticity is not decreased, but increased. However, this hardened alloy, after a period of time (such as 4 ~ 6 day and night), the strength and hardness will be significantly increased, and the plasticity will be significantly reduced. The phenomenon that the strength and hardness of aluminum alloy increase significantly with time after quenching is called aging. Aging can occur at room temperature, called natural aging, can also occur in a temperature range higher than room temperature (such as 100 ~ 200℃), called artificial aging.
3. Aging strengthening principle of aluminum alloy
Aging hardening of aluminum alloy is a rather complex process, which not only depends on the composition and aging process of the alloy, but also depends on the defects caused by shrinkage of the alloy in the production process, especially the number and distribution of vacancy and dislocation. At present, it is generally believed that aging hardening is the result of the formation of solute atoms.
Aluminum alloy in quenching heating, the formation of vacancy in the alloy, in quenching, because of the rapid cooling, these vacancy too late to move out, are "fixed" in the crystal. These vacancies in the supersaturated solid solution are mostly bound to solute atoms. Since the supersaturated solid solution is in an unstable state, it must change to an equilibrium state.
The size and number of hardened areas depend on the quenching temperature and quenching cooling rate. The higher the quenching temperature is, the greater the vacancy concentration is, the more the number of hardened areas is, and the size of hardened areas decreases. The greater the quenching cooling speed is, the more vacancies are fixed in the solid solution, which is conducive to increasing the number of hardened areas and reducing the size of the hardened areas.
One of the basic characteristics of precipitation hardening alloy systems is the equilibrium solid solubility which varies with temperature, that is, the solid solubility increases with the increase of temperature.