Effects of Element Y on Grain Refinement and Mechanical Properties of Cast Al-2.2Li-1.5Cu-Based Alloy

Abstract:

The effect of trace addition of 0.1wt% Y on the grain refinement and mechanical properties of Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc alloys at as-cast and heat-treated states was investigated. Results show that the addition of 0.1wt% Y into the Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc alloys can elevate the nucleation temperature of the Al₃(Sc, Zr) phase, leading to the preferential precipitation of the Al₃(Sc, Zr) phase and increasing the amount of Al₃(Sc, Zr) phase in the matrix. Al₃(Sc, Zr) phase can also act as a heterogeneous nucleation site in the α-Al matrix to promote nucleation and refine grains. The addition of element Y changes the precipitation phase characteristics at the grain boundaries in the as-cast alloy, which changes the distribution characteristics of secondary phases from initially continuous and coarse strip-like distribution at grain boundaries into the discontinuous dot-like and rod-like distribution. Besides, the size of secondary phases becomes smaller and their amount increases. Under the combined effects of grain refinement strengthening and precipitation strengthening, the Al-2.2Li-1.5Cu-0.5Mg-1Zn-0.2Zr-0.2Sc-0.1Y alloy after 175 °C/10 h aging treatment achieves an ultimate tensile strength of 412 MPa and an elongation of 6.3%. Compared with those of the alloy without Y addition, the ultimate tensile strength and elongation of the added alloy increase by 16.1% and 53.7%, respectively.