Study of Microstructure Scale and Regulation of Mechanical Properties of Al-6Si Hypoeutectic Alloy

The presence of a large amount of mesh-like eutectic Si structure and coarse α-Al dendrites in hypoeutectic Al-Si alloys leads to the degradation of their mechanical properties. Improving the microstructure of Al-Si alloys is the key to improve their properties. In this paper, the microstructure and mechanical properties of the alloy prepared with different methods were compared, where the alloy was prepared by adding rare earth Eu and Sb elements and/or by applying ultrasonic oscillation in the semi-solid state. The results show that different treatment methods have different effects on the physical microstructure of the Al-6Si alloy. Addition of Eu and Sb with a mass content of 0.5% each refined the eutectic structure, with little effect on α-Al. Applying 700 W ultrasonic treatment in the semi-solid alloy slurry effectively broke up the α-Al dendrites precipitated first in Al-6Si. Adding 0.5% Eu and 0.5% Sb to the alloy and applying ultrasonic treatment at 620 °C resulted in dispersed fine fibrous granular eutectic structure and rose-shaped α-Al grains. The tensile strength and elongation of the alloy were about 160 MPa and 20%, respectively, which were 52.13% and 96.87% higher than those of conventionally produced Al-6Si.