Effect of Solution and Aging Treatment on Microstructure and Mechanical Properties of Al–14Si–5Cu–1.1Mg–2.3Ni–0.3La Alloy

In this study, the effects of different heat treatment process parameters on the microstructure and mechanical properties of Al–12Si–5Cu–1.1Mg–2.3Ni–0.3La alloy were explored. Research showed that eutectic Si underwent three stages during solution treatment: diffusing, spheroidization and coarsening. As the solution temperature and time increased, the size of eutectic Si showed a trend of first decreasing and then increasing. Compared with the heat treatment time, the heat treatment temperature had a more significant effect on the mechanical properties. The coarsening of microstructure was the main reason for the deterioration of mechanical properties. The Al₃Ti and Al₃CuNiLa in the microstructure after aging can significantly improve the mechanical properties of the alloy. The Al₁₁La₃ with secondary precipitation occurred in the La-rich phase. The addition of La inhibited the growth of coherent/semi-coherent θ and β phases, which was very beneficial for the improvement of high-temperature strength. Under the optimal heat treatment process parameters of 500 °C × 4 h + 190 °C × 4 h, the ultimate tensile strength (UTS) of the alloy reached 366.65 MPa. The high-temperature strength and elongation of the alloy reached 101.98 MPa and 13.77% at 350 °C, respectively.