Genetic behavior of Al-Sr-Ti-C master alloy from casting to continuous rheo-extrusion and its refinement and modification effects on A356 alloy

The grain refinement and Si phase modification of A356 alloy are important for the improvement of mechanical properties, so the development of a master alloy for the refinement and modification of A356 alloy is very necessary. In this work, an Al-5Sr-5Ti-0.2C master alloy prepared by the fluoride salt method, and continuous rheo-extrusion (CRE) technology was introduced. The phase and microstructure of Al-5Sr-5Ti-0.2C were analyzed using XRD, SEM, and TEM, and the genetic behavior of Al-5Sr-5Ti-0.2C on the microstructure and tensile properties of A356 alloy was investigated. Different from the conventional casting method, CRE process can break the TiAl₃ and Al₄Sr phases in Al-5Sr-5Ti-0.2C alloy and promote the uniform distribution of TiC particles. Also, CRE Al-5Sr-5Ti-0.2C acquired the best refinement and modification effect on A356 alloy at the addition of 0.6 wt%, which led to the refined size of 231 ± 14 μm for α-Al grain and 1.75 ± 0.29 μm for eutectic Si in A356 alloy. Simultaneously, the optimal ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) of refined A356 alloy were 191.8 MPa, 93.4 MPa, and 10.1%, respectively, 23.5%, 9.7%, and 110.4% higher than the original A356 alloy.