Microstructural characteristics and mechanical properties of cast Al-3Li-xCu-0.2Zr alloy

The microstructures and mechanical properties of cast Al-3Li-xCu-0.2Zr alloy were investigated. The results showed that Cu addition could slightly refine the grain size of as-cast alloy. Cu element was significantly enriched at the grain boundaries, and Cu-rich intermetallic compounds were formed in the Cu-containing alloys during casting. The peak hardness increased and the time to peak ageing decreased with the increase of Cu content. Cu addition also had a pronounced influence on the precipitation behavior of Al-3Li-xCu-0.2Zr alloys, i.e. the number density, size and distribution of T1-Al2CuLi and θ′-Al2Cu phases. The tensile strength was effectively improved after 2 wt% Cu addition compared with Al-3Li-0.2Zr alloy. A good combination of strength to ductility could be obtained in Al-3Li-2Cu-0.2Zr alloy after solution and ageing 32 h at 175 °C. The precipitation-free zones (PFZs) were developed with the coarsening of δ′-Al3Li particles in the peak-aged (PA) and over-aged (OA) state, promoting the poor ductility and premature failure.