1. annealing treatment: the process of heating aluminum alloy castings to a higher temperature, generally around 300℃, holding for a certain time, and then cooling to room temperature with the furnace is called annealing. In the annealing process, the solid solution decomposes and the second phase particles gather, which can eliminate the internal stress of the casting, stabilize the casting size, reduce the deformation and increase the plasticity of the casting.
2. Solution treatment: heat the casting to as high a temperature as possible, close to the melting point of * * * crystal, keep it at this temperature for a long time, and then cool it quickly, so as to dissolve the strengthening components to the maximum extent. This high-temperature state is fixed and preserved at room temperature, which is called solid solution treatment. Solution treatment can improve the strength and plasticity of castings and the corrosion resistance of alloys.
3. Aging treatment The process of heating the casting after solution treatment to a certain temperature, keeping the temperature for a certain time, then taking it out of the furnace and slowly cooling it to room temperature in the air is called aging. If aging strengthening is carried out at room temperature, it is called natural aging, and if aging strengthening is carried out above room temperature and kept for a period of time, it is called artificial aging. Aging treatment is a spontaneous process of supersaturated solid solution decomposition, which restores the lattice of alloy matrix to a relatively stable state.
4. Cold and hot cycle treatment: the lattice of solid solution shrinks and expands due to repeated heating and cooling, which makes the lattice of each phase shift a little, so that the second phase particles are in a more stable state, thus improving the dimensional stability of castings, and is suitable for manufacturing precision parts.
Aluminum alloy has no tendency to brittle fracture at low temperature. With the decrease of temperature, the mechanical properties change and the strength increases, but the plasticity decreases very little. Therefore, sometimes in order to reduce or eliminate the internal stress of the casting, the cast or quenched casting can be cooled to -50℃, -70℃ or lower for 2-3h, then heated to room temperature in air or hot water, or artificially aged.