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Heat treatment of Aluminium Alloy

In the field of aluminum alloy casting, the improvement of material properties often depends on the quality of the heat treatment process. Different from simple casting, heat treatment can achieve more significant changes in the internal structure of aluminum alloys by precisely controlling temperature and time, thereby unlocking deeper performance potential.

Annealing is an indispensable part of heat treatment.

Aluminum alloys that have been cast or processed often exhibit internal stresses. If left untreated, it will directly affect subsequent processing and finished product performance. The annealing process involves heating to a specific temperature, holding at a certain temperature, and then slowly cooling to promote atomic migration and diffusion, effectively eliminating internal stress, making the structure more uniform and stable, and greatly improving plasticity.

Taking the homogenization annealing of ingots as an example, after being held at high temperature for a long time and cooled at a specific rate, the composition and structure become more uniform, the plasticity can be increased by about 20%, the extrusion pressure can be reduced by 20%, the extrusion speed can be increased by 15%, and the surface treatment quality can also be significantly improved. Intermediate annealing and complete annealing can be flexibly applied to different processing stages to meet diverse production needs.

Secondly, it is solid solution quenching. As a core step that can be used to strengthen aluminum alloys through heat treatment, this process heats the alloy to a higher temperature and keeps it warm, allowing the soluble phase to fully integrate into the aluminum matrix, forming a supersaturated solid solution. Then, it is rapidly cooled to "lock" it at room temperature, laying the foundation for subsequent precipitation strengthening.

According to the different quenching sensitivities of alloys, online or offline quenching methods can also be used.

Alloys with lower sensitivity can be cooled by air or water mist using extrusion waste heat; High sensitivity alloys require reheating and insulation, followed by rapid water or oil quenching. The processed aluminum alloy has better plasticity, making it easier to perform cold processing or straightening.

Timeliness is the ultimate critical stage for achieving performance enhancement. After solid solution quenching, aluminum alloys that have been maintained at room temperature or heating conditions for a period of time will gradually decompose into supersaturated solid solutions, precipitate small strengthening phases, and distribute around the α (Al) grain boundaries, significantly improving material strength.

Some alloys, such as 2024, can be strengthened under natural aging, while alloys like 7075 require manual aging. By precisely controlling temperature and time, the strengthening effect can be adjusted, and even under aging, over aging, and multi-stage aging can be achieved to meet different performance requirements.

It is worth mentioning that different aluminum alloy compositions have different heat treatment "codes".

Taking 6061 alloy as an example, it mainly contains magnesium and silicon elements. After homogenization treatment at 560 ℃ for 9 hours, the Mg2Si phase can be fully dissolved, creating conditions for the formation of strengthening phases during subsequent aging, thereby significantly improving strength. However, stable phases such as α (Al8Fe2Si) and β (Al5FeSi) are difficult to dissolve even at higher temperatures, so precise setting of process parameters is particularly crucial.

For casting enterprises, mastering the heat treatment process means being able to accurately determine the temperature, time, and cooling method for heat treatment based on the alloy type and product requirements, thereby significantly improving material properties.

Summary at the end

Whether it is aerospace, automotive manufacturing, or electronic devices, the high-end field has increasingly high requirements for the strength, lightweight, heat dissipation, and processing performance of aluminum alloys. Precise heat treatment is a powerful support for achieving product upgrades and technological breakthroughs.