Dual characteristic of trace rare earth elements in a commercial casting Al-Cu-X alloy

摘要

The effect of rare earth elements on microstructure and mechanical properties of casting Al–Cu–X alloy(X = Mn, Ti, V, Cd, Zr) was investigated in as-cast and T6 conditions. Microstructure evolution was characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy. REcontaining intermetallic compounds(IMCs) formed in this alloy were indentified by X-ray diffraction(XRD) and energy dispersive spectroscopy(EDS). It is shown that the additions of RE(60Ce–40La, wt%) result in the formation of Ce-rich blocky-shaped Al20(Ti, V)2RE and La-rich skeletal-shaped Al8Cu4 RE. Tensile results of samples after T6 treatment indicate that the strength and ductility increase slightly to 480 MPa and 9.7 %, respectively, with RE content increasing from 0 wt% to 0.3 wt%. This is due to the combinative hardening effects of reduced grain size,enhanced precipitation of h0(Al2Cu) phase and Al20Cu2Mn3 dispersed particles, and minor La-rich IMCs at the grain boundaries of a-Al dendrites. The decrease of strength of 0.5 wt% RE-added sample is ascribed to the aggregation of Al20(Ti, V)2RE IMCs inside the grains. The dual characteristic of rare earth elements was also discussed in terms of its positive and negative effects on mechanical properties.