Abstract

An experimental study has been undertaken for the weldability of Al-alloy A5052-HR32 using the modulation effect to overcome the cracking problem. The experiments were carried out with a multiwave Nd-YAG laser of which power could be varied from CW to pulse mode with square and sine wave modulation function. The samples ranging in thickness from 1 mm to 2mm were bead on plate, butt and lap welded. For the efficient coupling and to prevent the back reflection into the cavity, the incident beam angle was set at 10 degrees to the normal (Fig.1). A cross flow nozzle was used against the spattering and to suppress the plasma plume, thus enhancing the penetration depth. The shielding gas, argon was applied in the front, back and bottom groove of the fixture so as to shield the hot newly soldified weld metal as it emerges from the laser beam. The result indicate that because of high solidification rate, a very fine dendritic microstructure is developed in the fusion zone (Fig.2). Besides that microstructural characterization of the weldment revealed urn order porosity that occured in the welded region. The level of cracks and porosity in the high duty cycle welds were significantly less than that encountered in the low duty cycle weldment. Whereas the microhardness data result indicate that the weld metal and the heat affected zone were as hard as the base metal.

© 1996 IEEE