Customized by aluminum casting manufacturer
In the actual heat treatment of aluminum castings, solution treatment is a process. It can improve the strength, plasticity and corrosion resistance of aluminum alloy castings. What are the factors that affect the effect of solution therapy? Here are three main factors for you to answer:
1. Solution temperature. The higher the temperature is, the faster the dissolving speed and quantity of strengthening elements are, and the better the strengthening effect is. Generally speaking, the upper limit of the heating temperature is lower than the initial overburning temperature of the aluminum alloy casting, and the lower limit of the heating temperature should make the strengthening composition dissolve in the solid solution as much as possible. In order to obtain the effect of solution strengthening without overburned alloy, the step heating method is adopted, that is, the temperature is kept at the low melting point eutectic temperature, so that there is no low melting point eutectic after composition diffusion and dissolution. Then rise to a higher temperature for heat preservation and quenching. For example, ZL201 Alloy is a solution treatment with staged heating.
2. Waiting time. It depends on the dissolution rate of the strengthening elements, which depends on the type, composition, structure, casting method, shape and wall thickness of the casting. The heat preservation time of cast aluminum alloy is much longer than that of deformed aluminum alloy. Generally, it is determined by test that the length of common sand casting is 20% - 25% longer than that of the same type of metal casting.
3. Cooling rate. The higher the cooling rate, the higher the supersaturation of high temperature solid solution and the higher the mechanical properties of castings. However, the greater the internal stress, the greater the possibility of casting deformation. The cooling speed can be changed by choosing cooling medium with different heat capacity, thermal conductivity, latent heat of evaporation and viscosity. In order to obtain the minimum internal stress, aluminum castings can be cooled in a hot medium (boiling water, hot oil or molten salt).
In order to ensure high mechanical properties and low internal stress of aluminum castings after quenching, isothermal quenching is sometimes used by aluminum casting manufacturers. That is to say, the solution treated aluminum castings are quenched in 200-250 ℃ hot medium for a certain time, and the solution treatment is combined with aging treatment.