Effect of Microalloying with La on the Microstructure and Mechanical Properties of A356 Alloy for Low-pressure Casting of Wheel Hubs

The effects of microalloying with La on the microstructure and mechanical properties of A356 alloy wheels in the as-cast state and after solution treatment plus aging (referred to as the T6 state) under low-pressure casting conditions were investigated using optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and a universal tensile testing machine. The results showed that the grain refinement of wheel hub A356 alloy was more obvious after the addition of 0.08% wt. %La, and the secondary dendrite arm spacing was reduced from 27.73 μm to 25.94 μm in the outer rim organization, and the secondary dendrite arm spacing was reduced from 49.11 μm to 47.68 μm at the core of the wheel. It was observed by TEM that after the addition of the rare earths, the AlSiLa phase in the outer rim organization at the end of the <italic>β</italic>-AlSiFe phase grows at the end of the <italic>β</italic>-AlSiFe phase, and it can be concluded that the AlSiLa phase can effectively hinder the growth of the <italic>β</italic>-AlSiFe phase. Moreover, spherical nanosized AlMgLa phase was also found in the T6 state, which can enhance the mechanical properties of the alloy. In the as-cast state, the addition of 0.08%La(Mass fraction) increased the yield strength at the outer rim from 132.9 MPa to 147.09 MPa, which is about 10.7%, and the elongation from 15.72% to 16.52%, which is about 5.1%; in the T6 state, the yield strength at the outer rim increased from 178.8 MPa to 195.57 MPa; and the yield strength at the core from 180.19MPa to 190.69 MPa.