Effect of Different Ageing Processes on Microstructure and Mechanical Properties of Cast Al–3Li–2Cu–0.2Zr Alloy

Abstract

The effect of different ageing processes on microstructure and mechanical properties of cast Al–3Li–2Cu–0.2Zr alloy was investigated using transmission electron microscopy and tensile tests. The results showed that the mean size of δ′-Al3Li particles and the number density of Cu-rich precipitates both increased with increasing ageing temperature from 150 to 190 °C for 24 h, resulting in increasingly high strength. In contrast, the ductility deteriorated with the increase in ageing temperature as a result of the intensified planar slip. The duplex low-to-high ageing treatment (120 °C for 6 h followed by 160 °C for 24 h) was shown to be beneficial to the ductility compared with the corresponding single-stage ageing treatment (160 °C for 24 h). The reduced slip length induced by the precipitation of θ′-Al2Cu phases was found to be mainly responsible for this ductility improvement.