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

用Al-10Sr变质剂和Al-5Ti-B细化剂处理A356铝合金熔体，并结合挤压铸造和T6热处理工艺，研究变质细化与热处理对A356铝合金挤压铸造件的组织和性能的影响规律。结果表明，随着Al-10Sr变质剂加入量的增加，共晶Si的形貌由片状和长杆状变为颗粒状和蠕虫状，α-Al的晶粒尺寸先减少后增大。当Al-10Sr的加入量(质量分数)为0.3%时，挤压铸造成形件的最优抗拉强度、屈服强度和延伸率分别为221.3 MPa、104.5 MPa和10.3%。Al-10Sr变质能提高形核率、细化α-Al晶粒尺寸和改变共晶硅形貌，使铸造件的力学性能提高。随着A-5Ti-B的增加，晶粒尺寸先降后增，力学性能先增后降。Al-5Ti-B的加入量为0.6%时，最优抗拉强度、屈服强度和延伸率分别为215.6 MPa、106.6 MPa和9.0%。T6热处理(固溶540℃/4 h+时效190℃/4 h)使屈服强度和抗拉强度显著提高和延伸率降低。经过0.6% 的Al-5Ti-B细化处理，T6处理挤压铸造件的最优的抗拉强度、屈服强度和延伸率分别为297.5 MPa、239.3 MPa和8.0%。共晶硅的球化和细化、成形件成分的均匀化以及Mg₂Si强化相在基体中弥散析出，是热处理后构件力学性能提高的主要原因。

Influence of Modification,Refinement and Heat Treatment on Mechanical Properties of A356 Al-alloy Components Prepared by Squeeze Casting

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.