Solution treatment is to heat the casting to the highest possible temperature, close to the melting point of the eutectic. The higher the temperature, the faster the dissolution of strengthening elements and the better the strengthening effect. Generally, the upper limit of the heating temperature is lower than the temperature at which the alloy starts to burn, and the lower limit should make the strengthening components dissolve into the solid solution as much as possible. Keep at this temperature for a long enough time to maximize the dissolution of the strengthening components. This high-temperature state is fixed and stored at room temperature. The holding time is determined by the dissolution rate of the strengthening elements, which depends on the type, composition, and composition of the alloy. Structure, casting method, shape and wall thickness of castings.
Rapid cooling, the greater the cooling rate given to the casting during quenching, the higher the oversaturation temperature of the solid solution preserved from the high temperature state, so that the casting obtains high mechanical properties, but at the same time, the greater the internal stress formed, the higher the oversaturation temperature of the solid solution. The greater the possibility of deformation, it has a great relationship with the temperature of the cooling medium. This process is called solution treatment. Solution treatment can increase the strength and plasticity of castings and improve the corrosion resistance of the alloy. The quenching transfer time of solution heat treatment should be as short as possible, generally should not exceed 15s, so as to avoid the diffusion and precipitation of alloying elements and reduce the performance of the alloy.
Aging treatment: (equipment: aluminum alloy aging furnace)
Aging treatment is the process of heating the aluminum alloy castings after solution treatment to a certain temperature, holding them for a certain period of time, and then slowly cooling them to room temperature in the air. The process is called aging. If the aging strengthening is performed at room temperature, it is called natural aging, and if the aging strengthening is performed at a temperature higher than room temperature and kept for a period of time, it is called artificial aging. The aging treatment is undergoing a spontaneous process of decomposition of the supersaturated solid solution, so that the lattice of the alloy matrix is restored to a relatively stable state.
The choice of aging temperature and time depends on the requirements for alloy properties, the characteristics of the alloy, the degree of supersaturation of the solid solution, and the casting method. Artificial aging can be divided into three categories: incomplete artificial aging, complete artificial aging and overaging. Incomplete artificial aging is to use a relatively low aging temperature or a short holding time to obtain excellent comprehensive mechanical properties, that is, to obtain relatively high strength, good plasticity and toughness, but the corrosion resistance may be relatively low. Full artificial aging uses a higher aging temperature and a longer holding time to obtain the greatest hardness and the highest tensile strength, but the elongation is low. Over-aging is carried out at a higher temperature. At this time, the alloy maintains a higher strength and at the same time the plasticity is improved, mainly for obtaining good stress corrosion resistance. In order to obtain a stable structure and geometric size, the time effect should be performed at a higher temperature. Over-aging is usually divided into stabilization treatment and softening treatment according to usage requirements.
T6 heat treatment of aluminum alloy castings is generally divided into two stages, solution treatment (quenching) and aging aluminum alloy die casting.
Solution treatment: refers to the heat treatment process of heating aluminum alloy castings to a certain temperature and keeping it constant for a period of time, so that the excess phase is fully dissolved in the solid solution and then rapidly cooled to obtain a supersaturated solid solution, improve mechanical properties, and enhance corrosion resistance.
Aging treatment: Aging is a heat treatment that completes the T6 process of aluminum alloy castings after solution treatment. Aging treatment is to use a higher aging temperature and a longer holding time to obtain the greatest hardness and the highest tensile strength, and achieve dimensional stability aluminum alloy die-casting.
