Comprehensive regulation of mechanical properties and thermal conductivity of Al-Si-Fe alloys through the mixed-additive (Sr and TiB2) strategy

Abstract

It is of both scientific and technical significance to adjust the balance between the thermal conductivity and mechanical performance of Al-Si alloys. In this work, we proposed a strategy of using mixed-additive to perform such tuning. A permanent mold casting (PMC) was used to optimize the as-cast properties based on the orthogonal combination of Sr and TiB2. It is anticipated that the addition of Sr addition can modify the eutectic Si, while the addition of TiB2 can refine the primary α-Al dendrites, with uncertainty of its effects on the modification efficiency of Sr. The results showed that addition of TiB2 does not impair the modification efficiency of Sr. The optimized composition contained 200 ppm Sr and 300 ppm Ti. Casting specimens were then prepared using high-pressure die casting (HPDC) process. The results demonstrated that significant reduction in the size of β-AlFeSi, eutectic Si, and α-Al grains can be achieved by HPDC process. As a result, the tensile properties have been improved. The natural effects of HPDC process on the alloy, however, such as microstructure refinement and variation in porosity, leading to deduction in the thermal conductivity to 148.5W/(m·K). This value still exceeds conventional alloys nevertheless.