Effects of Sr/Ca Composite Modification and Heat Treatment Process on the Microstructure, Mechanical Properties and Thermal Conductivity of Semi-solid Al–6Si–0.6Mg–0.1Sc Alloy

Abstract

Aluminum alloys are the first choice for the preparation of integrated structure–function materials, but the conflicting relationship between mechanical properties and thermal conductivity limits the application of aluminum alloys. This study takes Al–6Si–0.6Mg–0.1Sc alloy as the subject of research. It adopts the semi-solid rheological die-casting process, combines composite modification and heat treatment methods to prepare aluminum alloy materials with high strength and high thermal conductivity. Meanwhile, X-ray, OM, SEM, TEM, XRD, tensile test and thermal conductivity test were used to study the changes in the microstructure and properties, and to reveal its strengthening and thermal conductivity mechanism. The results show that the composite addition of Sr/Ca can effectively improve the morphology of Al–Si eutectic phase and Mg₂Si phase in Al–6Si–0.6Mg–0.1Sc alloy, which changes the Al–Si eutectic phase from its original lamellar shape into fine granular particles, increasing the electron channels and mean free paths. As a result, the mechanical properties and thermal conductivity of the alloy are enhanced. After the semi-solid die-cast Al–6Si–0.6Mg–0.1Sc alloy undergoes T6 heat treatment (470 °C × 4 h + 180 °C × 12 h), the improvement of the microstructure morphology and the distortion of the internal lattice lead to the simultaneous enhancement of both the mechanical properties and the thermal conductivity of the alloy. The tensile strength, yield strength and elongation of the alloy in the T6 state reach 327 MPa, 196 MPa and 6.5%, respectively, and the thermal conductivity reaches 156.1 W/m K. The tensile strength and thermal conductivity of the alloy are 16% and 13.2% higher than those of the semi-solid die casting, respectively.

Graphic Abstract