变质细化和热处理对挤压铸造成形A356铝合金构件性能的影响

Influence of modification, refinement and heat treatment on the microstructure and mechanical properties of A356 Al-alloy components prepared by squeeze casting was investigated. The results show that with increase of Al-10Sr modification agent, the morphology of eutectic Si changed from lamellar, rod-like shape to granular and wormlike shape, and the grain size of α-Al increased first and then decreased. When 0.3% Al-10Sr modification agent was added, the optimal mechanical properties of squeeze casting components including ultimate tensile strength of 221.3 MPa, yield strength of 104.5 MPa and elongation of 10.3% were achieved. The improvement of mechanical properties can be attributed to the increase of nucleation rate, the decrease of α-Al grain size and the change of eutectic Si morphology by adding 0.3% Al-10Sr modification agent. With the increase of A-5Ti-B refiner, the α-Al grain size first decreased and then increased, but the changing trend of mechanical properties is inverse. When 0.6% Al-5Ti-B refiner was added, the optimal ultimate tensile strength, yield strength and elongation were 215.6 MPa, 106.6 MPa and 9.0%, respectively. T6 heat treatment including solid solution at 540℃ for 4 h and artificial aging at 190℃ for 4 h led to the improvement of yield strength and ultimate tensile strength, but it led to the decrease of elongation. The optimal mechanical properties such as yield strength of 239.3 MPa, ultimate tensile strength of 297.5 MPa and elongation of 8.0% were obtained for the squeeze casting component with T6 treatment and an addition of 0.6% A-5Ti-B refiner. The globularization of eutectic Si, the refinement of eutectic Si, the homogenization of composition for the prepared component and the precipitation of Mg₂Si phase in α-Al matrix all lead to the improvement of mechanical properties of squeeze casting component with T6 treatment.