Cu/Li Ratio on the Microstructure Evolution and Corrosion Behaviors of Al– x Cu– y Li–Mg Alloys

The microstructure evolution and the corrosion feature of Al–xCu–yLi–Mg alloys (x:y = 0.44, 1.65 and 4.2) were systematically investigated under the same artificial aging conditions. The relationships between types of precipitates and mechanical performance, as well as electrochemical behaviors, were discussed. Our results show that different types of precipitates can be obtained in alloys with different Cu/Li mass ratios, which significantly influences the mechanical performance of the alloys and substantial corrosion behaviors. Specifically, the analogous corrosion evolution in the aging Al–xCu–yLi–Mg alloys was first ascertained to be derived from the growth mechanism of the precipitates at the grain boundary (GB). Moreover, a small number of GB precipitates can be obtained in the aged alloy with the lowest Cu/Li mass ratio, thereby resulting in the largest intergranular corrosion resistance. A higher proportion of the GB T1 phase in the continuous precipitates induces higher corrosion sensitivity in alloy with a high Cu/Li mass ratio.