Microstructure and mechanical properties of laser welded joints of Al-Cu-Li and Ti-Al-V alloys

This paper presents the results of studies of dissimilar butt laser welds of a thermally strengthened aluminum-lithium alloy of the Al-Cu-Li system and a titanium alloy of the Ti-Al-V system. The main variable parameter was the laser offset relative to the joint. Microstructure of the weld metal, the results of tensile tests as well as fractography of the fracture surfaces were shown. It was found that the microstructure of the aluminum alloy was of the dendrite type, and that of the titanium alloy was martensitic. An intermetallic layer was formed between them. The offset towards the titanium alloy plate reduced the thickness of the intermetallic layer from similar to 400 mu m (offset was 0) down to 2.5 and 0.7 mu m (offset was 0.5 and 1.0 mm, respectively). Also, the transformation of its structure from brittle to ductile was observed. The ultimate tensile strength of the joints increased from 103 MPa (offset was 0) up to 213 and 272 MPa when offset was 0.5 and 1.0 mm, respectively. When offset was 1 mm, the weld metal failure occurred predominantly through the aluminum alloy. This indicates that the ultimate tensile strength of the intermetallic layer was higher than that of the Al-Cu-Li alloy. It is most likely that the mechanical properties of the intermetallic layer substantially depended on the composition of the alloying elements of the aluminum alloy.