Effect of the structure and the phase composition on the mechanical properties of Al-Cu-Li alloy laser welds

The purpose of these investigations was to study the effect of heat treatment on the structure and the phase composition of laser welded joints of the Al-2.8Cu-1.7Li alloy (V-1461 grade), providing the maximum tensile strength. To study the phase composition of the weld metal, synchrotron radiation was applied using a 'Mega Science' facility. This enabled to assess the phase distribution across the weld metal before and after heat treatment. It was found using high-resolution scanning and transmission electron microscopy, energy dispersive X-ray analysis, and synchrotron X-ray diffractometry that the T-1(Al2CuLi) and T-2(Al6CuLi3) main phases had been formed in the weld metal and at the interfaces with the matrix. Ultimate tensile strength of the welded joints was about 341 MPa, which was 62% of that of the base metal. Subsequent heat treatment of the welded samples, included hardening and artificial aging, caused the homogenization of the Al-Cu-Li alloy solid solution, as well as the formation of the delta' (Al3Li) hardening phase. Also, the T-1 and T-2 phases were formed partially. After quenching, tensile strength of the welded joints improved and was about 85% of that of the base metal. After artificial aging, it was about 510 MPa and approached tensile strength of the base metal (93%).

Automated summary

The study found that the main phases T-1 and T-2 as well as the δ' hardening phase were formed in the heat-treated Al-2.8Cu-1.7Li alloy laser welded joints, resulting in an improved tensile strength. After quenching, the tensile strength of the welded joints was about 85% of that of the base metal, and after artificial aging, it approached 93% of the base metal's tensile strength.