As you know, In life; we often see aluminum gravity die casting parts, which are durable, and like by us, However, do you know they cast out need to be heat treatment? in this article, we will discuss the heat treatment of Aluminium castings.
The purpose of heat treatment
The purpose of heat treatment of aluminum alloy castings as below.
- Improve the mechanical properties and corrosion resistance, stabilize the size.
- Improve the machining performance; such as cutting and welding.
- Because the mechanical properties of casts cannot meet the requirements of usage; except for ZL102; ZL302 and ZL401. rest of cast aluminum alloys should be heat treated to improve the mechanical properties; specifically in the following aspects.
A. Eliminating the internal stress; Improve solidification of the casting;
B. improve the mechanical strength and hardness of the alloy, to ensure that the alloy has a certain degree of plasticity and cutting performance, welding performance.
C. stabilize the organization and size of the casting to prevent and eliminate high temperature changes that cause volume changes.
D. Eliminate inter-granular and compositional segregation to homogenize the organization.
Methods of heat treatment
1. Annealing treatment
Annealing treatment is to eliminate the casting stress caused by machining, stabilize the shape and size of the machined parts, improve the plasticity of the alloy.
Process:
- Heat The aluminum alloy castings to 280-300 ℃, and holding 2-3 hours.
- With the furnace cooling to room temperature, so that the solid solution slowly decomposition, precipitation of the second mass point aggregation, so as to eliminate the internal stress of the casting, to achieve the purpose of stabilizing the size, improve plasticity, reduce deformation, warp.
2. Quenching
Heat the castings to higher temperature; generally, close to the melting point, more than 500 ℃. holding over 2 hours. so that the soluble phase within the alloy is fully dissolved.
Then, Quench the castings into water at 60-100℃, so that Cooled down the casting; to maximize the dissolution of the reinforcing elements in the alloy and fixed to room temperature. This process also called solution treatment or cold treatment.
3. Aging treatment
Ageing treatment, also known as low-temperature tempering, is the quenching of aluminum alloy castings heated to a certain temperature, holding a certain amount of time out of the furnace air-cooled to room temperature, so that the supersaturated solid solution decomposition, so that the alloy matrix organization stable process.
Aging treatment include natural aging and artificial aging.
Natural aging refers to the aging strengthening at room temperature.
Artificial aging include incomplete artificial aging, complete artificial aging, over-aging 3 kinds.
A incomplete artificial aging:
Heat the castings to 150-170 ℃, and holding 3-5 hours, in order to obtain good tensile strength, good plasticity and toughness, but lower corrosion resistance heat treatment process.
(2) complete artificial aging:
Heat the castings to 175-185 ℃; and holding 5-24 hours, in order to obtain sufficient tensile strength (i.e., the highest hardness) but low elongation heat treatment process.
(3) over-aging:
Heat the casting to 190-230 ℃, holding 4-9 hours, so that the strength has decreased, plasticity has increased, in order to obtain a better stress resistance, corrosion resistance process, also known as stabilization tempering.
Conclusion
Heat treatment is an important part of casting, which determines the life, mechanical properties, hardness, etc. of the casting. As a professional aluminum casting foundry; we have rich experience in gravity die casting; if you have similar project need to develop. please contact us.