Formation of a crack-free joint between Ti alloyand Al alloy by using a high-power CO2 laser

Abstract

The present paper aims at producing a crack-free weld between a commercially available Ti alloy (Ti-6 wt% Al-4 wt% V) and a wrought Al alloy (Al-1 wt% Mg-0.9 wt% Si). Ti alloy and Al alloy with a plate thickness of 3 mm are butt welded using a 2.5 kW continuous CO2 laser. The laser power, welding speeds and offset of the laser with respect to the joint are considered as the variable parameters. It is observed that intermetallic compounds (mainly TiAl and Ti3Al) are formed in the fusion zone depending on the amount of Al and Ti melted by the laser. These intermetallic phases are very brittle and the solid-state cracks are formed near the Al side of the interface because of the stress developed after the solidification.

The formation of cracks is sensitive to the total Al content in the fusion zone. In order to minimize the dissolution of Al in the fusion zone and to increase the toughness of the intermetallic phases, Nb foil is added as a buffer between the Ti alloy and Al alloy workpieces. It is observed that the partially melted Nb acts as a barrier to dissolve Al in the fusion zone and facilitates a good joining condition for welding of Ti alloy with Al alloy.