Towards high performance Al–Si–Fe alloy castings via rheo-diecasting: Effect of injection velocity and heat treatment on microstructure evolution and property

The mechanical properties and thermal conductivity of Al–Si–Fe castings must meet high requirements in the automobile, aerospace, and communication fields. Traditional high-pressure diecasting (HPDC) castings often have dendritic structures and pore defects that deteriorate their overall performance. Therefore, an advanced rheo-diecasting (RDC) technique assisted by a vibrating contraction sloping plate was proposed to address this problem. However, the process optimization strategy, microstructural evolution, and performance improvement mechanisms remain unclear. The influence of the injection velocity on the microstructure, mechanical properties, and thermal conductivity of the RDC tensile specimens was first investigated. A high-performance cover plate was fabricated via RDC using an optimized injection velocity. The results showed that when the injection velocity increased to 2.8 m/s, the porosity decreased to a minimum value, and the mechanical performance and thermal conductivity of the RDC tensile specimens reached their maximum values. Furthermore, spherical eutectic Si phases and nanosized Mg2Si precipitates for the RDC cover plate were observed after T6 heat treatment, which further improved the mechanical properties and thermal conductivity owing to Orowan strengthening and decreased lattice distortion, respectively. The ultimate tensile strength, yield strength, elongation, and thermal conductivity for the RDC cover plate were 358.2 MPa, 279.9 MPa, 12.5%, and 180.72 W/(m·K), respectively, which were higher than that of reported similar alloys. From engineering perspectives, this study had the application value for produce of high-quality RDC castings.