Why Does Aluminum Alloy Casting Need Heat Treatment?
Aluminum alloy casting needs heat treatment process, as heat treatment is one method of surface treatment for most metal parts. In the last article we mentioned that the surface treatment is crucial to metal parts & plastic parts. Because it not only can increase wear resistance, corrosion resistance, friction coefficient and fatigue property but also make our parts looks more perfectly and durability.
Today we will continue to share new method of surface treatment process. Why does aluminum alloy casting need heat treatment, and its practical functions and methods.
What does aluminum alloy casting need heat treatment?
The purpose of heat treatment of aluminum alloy casting is to improve mechanical properties and corrosion resistance, stable dimension of the parts and improve machining properties. Such as: machining and welding etc.
At the same time, due to many of the mechanical properties of AS-cast alloy can’t meet the use requirement, only except for ZL102 AI-Si, AI-Mg of ZL401 alloy and AL-zinc, the rest of cast aluminum alloy need to through heat treatment to further improve the mechanical properties and other performance of the casting, specifically the following aspects:
- It can eliminate the internal stress caused by the uneven cooling speed ( such as: Uneven the casting structure)
- Improve the mechanical strength and hardness of castings, and improve the metallographic structure to ensure that the alloy has certain plasticity, cutting performance and welding property.
- Stabilize the structures and sizes of castings, and prevent and eliminate the temperature phase change, thus to change the final volume.
- Eliminate the segregation of intercrystalline and composition and homogenize the organization.
Below are some heat treatment machining methods for aluminum alloy casting
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Annealing process
Annealing process which is to eliminate casting stress of casting and the internal stress of the machining caused, and stable the shapes and size of the mechanical parts, improve the plasticity of the alloy and reduce the deformation and warping.
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Quenching Process
Quenching is to heat the aluminum alloy castings to a higher temperature( generally in close to the eutectic point or over 500℃) and keep this temperature for 2 hours to make the soluble solid fully dissolved in the alloy. Then rapid quenched into 60-100℃ water to make the casting cooled and let strengthen components get maximum dissolved in alloy components and fixed to room temperature. This process is called quenching, also known as a solid solution or cold treatment.
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Aging Process
The aging process is also called low-temperature tempering, which is to heat quenched aluminum alloy to a certain temperature, the heat preservation time on air cooling or room temperature, and decompose the supersaturated solid solution to make the alloy matrix organization stable process. In general, Aging treatment is divided into two categories: Natural aging and artificial aging.
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Circular process
It’s to cool the aluminum alloy casting to a temperature below zero ( such as- 50 ℃, 70 ℃, 195 ℃) and heat preservation time, then heat the alloy casting parts to 350℃ below, make the moderate solid solution alloy repeated contraction and expansion, and the grain will also have a small amount of displacement in each phase. To make these solid solutions in the crystal lattice atom partial area and intermetallic compound particle in a more stable state, to achieve the purpose of improving the size of the parts and stable volume. This machining process called a cycle process. It’s mainly suitable for these parts that are precise and stable in size (such as some parts on the testing apparatus), normal casting doesn’t do this.
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