The basic principle of heat treatment of cast aluminum alloy

(1) Annealing: The aluminum alloy gravity casting product is heated to a certain temperature and kept for a certain period of time, and then cooled to room temperature at a certain cooling rate. Through atomic diffusion and migration, the organization is made more uniform and stable, and the internal stress is eliminated, which can greatly improve the plasticity of the material, but the strength will be reduced.

(2) Solution quenching treatment: Heat the heat-treatable-strengthened cast aluminum alloy materials (such as A356, LM25, ZL101A, A357, ZL104, etc.) to a higher temperature and keep it for a certain period of time, so that the second phase or Other soluble components are fully dissolved in the aluminum matrix to form a supersaturated solid solution, and then the supersaturated solid solution is kept to room temperature by means of rapid cooling. It is an unstable state. There is a possibility of precipitation. However, at this time, the material has high plasticity and can be cold worked or straightened.

(3) Aging: The aluminum alloy die casting alloy parts after solution quenching are kept at room temperature or higher temperature for a period of time, the unstable supersaturated solid solution will decompose, and the second phase particles will be precipitated from the supersaturated solid solution ( or precipitation), distributed around the α(AL) aluminum grains, resulting in a strengthening effect called precipitation (precipitation) strengthening.

Natural aging: Some alloys (such as ZL301, etc.) can produce precipitation strengthening at room temperature, which is called natural aging.

Artificial aging: Some alloys (such as A356, etc.) do not have obvious precipitation strengthening at room temperature, but the precipitation strengthening effect is obvious at higher temperatures, which is called artificial aging.

Artificial aging can be divided into under-aging and over-aging.

①Unaging: In order to obtain a certain performance, control a lower aging temperature and maintain a shorter aging time.

②Over-aging: In order to obtain some special properties and better comprehensive properties, aging is carried out at a higher temperature or under a longer heat preservation time.

③Multi-stage aging: In order to obtain some special properties and good comprehensive properties, the aging process is divided into several stages. It can be divided into two-stage and three-stage aging