The effect of grain refinement and precipitation strengthening induced by Sc or Er alloying on the mechanical properties of cast Al-Li-Cu-Mg alloys at elevated temperatures

In present paper, the effect of Scandium and Erbium alloying on the microstructure evolution and mechanical performance at elevated temperature for Al-Li-Cu-Mg alloy are investigated. Furthermore, the interaction process between shell/core composite particles Al₃(M, Zr, Li) (M = Sc/Er) and dislocations is described in the paper. The experimental results indicate that 0.2 wt% Sc addition has much more significant effect upon refining grain of the alloys, compared to equivalent Er addition content. The addition of the both rare elements will obviously facilitates the precipitation density of the shell/core composite Al₃(M, Zr, Li) particles in the aging-treated alloys. Moreover, Sc addition will also contribute to promoting the precipitation of plate-like S/S′ phase during aging process. At 200 °C or below, the most excellent mechanical performance of Sc-containing alloy can be attributed to the synthetical effects of the grain refining, dislocation cutting (δ′-Al₃Li) and Orowan (shell/core composite Al₃(M, Zr, Li) particles) multiples mechanisms, although the fracture morphology of the alloy displays intergranular fracture features. While raising test temperature to 300 °C, it can be observed from the morphology of the Sc-containing alloy that the failure of the grain refining mechanism and the of grain boundary sliding (GBS) occurs that which will damage the high-temperature strength but increase deformation ability of samples. It should be noted that the large grain size and the precipitation of the composite Al₃(M, Zr, Li) particles are major reasons for the improvement of elevated-temperatures mechanical properties of the Er-containing alloy.