Among non-ferrous metals, aluminum and aluminum alloys are the most widely used type of metal structural materials, and their output is second only to steel. Therefore, it is of practical significance to research and develop the heat treatment process of aluminum alloy. The main heat treatment method of cast aluminum alloy is cast aluminum alloy It is to obtain the aluminum alloy of the casting by the method of casting.It is widely used in aviation, shipbuilding, instrumentation, machinery and other industrial sectors.
The heat treatment of aluminum alloy castings is to select a certain heat treatment specification, control the heating speed to rise to a certain temperature and keep it for a certain period of time and cool it at a certain speed to change the structure of its alloy.
- 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 the diffusion and migration of atoms, the organization is more uniform, stable, and internal stress is eliminated, which can greatly improve the plasticity of the material, but the strength will be reduced.
- Solution quenching treatment: heat-treatable and strengthened cast aluminum alloy materials (such as A356, LM25, ZL101A, A357, ZL104, etc.) are heated to a higher temperature and maintained for a certain period of time to make the second phase in the material 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 a rapid cooling method. It is an unstable state. Because it is in a high-energy state, the solute atoms There is a possibility of precipitation. However, at this time, the plasticity of the material is relatively high, and cold working or straightening procedures can be carried out.
- Aging: After solution quenching, the aluminum alloy gravity casting parts are kept at room temperature or higher temperature for a period of time, the unstable supersaturated solid solution will be decomposed, and the second phase particles will be precipitated from the supersaturated solid solution ( Or precipitation), distributed around the α(AL) aluminum grains, and the strengthening effect is 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.) are not obviously strengthened by precipitation at room temperature, but the effect of precipitation strengthening at higher temperatures is obvious, which is called artificial aging.
- Underaging: In order to obtain a certain performance, control a lower aging temperature and keep a short aging time.
- Overaging: In order to obtain some special performance and better comprehensive performance, aging is carried out at a higher temperature or a longer time of heat preservation.
- Multi-stage aging: In order to obtain some special performance and good comprehensive performance, the aging process is divided into several stages. It can be divided into two-stage and three-stage aging
Artificial aging can be divided into under-aging and over-aging.