FORMATION OF A CRACK-FREE JOINT BETWEEN TI ALLOY AND AL-ALLOY BY USING A HIGH-POWER CO2-LASER

The present paper aims at producing a crack-free weld between a commer cially 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 thicknes s of 3 mm are butt welded using a 2.5 kW continuous CO2 laser. The las er power, welding speeds and offset of the laser with respect to the j oint are considered as the variable parameters. It is observed that in termetallic 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 f ormed near the Al side of the interface because of the stress develope d after the solidification. The formation of cracks is sensitive to th e total Al content in the fusion zone. In order to minimize the dissol ution of Al in the fusion zone and to increase the toughness of the in termetallic phases, Nb foil is added as a buffer between the Ti alloy and Al alloy workpieces. It is observed that the partially melted Nb a cts as a barrier to dissolve Al in the fusion zone and facilitates a g ood joining condition for welding of Ti alloy with Al alloy.