Experimental Study on Butt-joint TC4/GH4169 Dissimilar Metals Prepared by Double Laser Assisted FSW

Abstract

Abstract To verify validity of new method for preparing dissimilar metals with high melting point through double laser assisted friction stir welding (FSW), butt welding tests on dissimilar metals of TC4 and GH4169 were carried out by conventional FSW, single laser assisted FSW and double laser assisted FSW, respectively. Macroscopic morphology, microstructure and mechanical properties of butt-joint were analyzed. Results demonstrated that the conventional FSW surface is relatively rough, manifested by existence of many trims and rags, incomplete mixing of joint and dissimilar materials, as well as a certain proportion of pore defects. The single laser assisted FSW surface is even and smooth, manifested with few trims and rags. Compared with conventional FSW, the dissimilar material mixing is improved significantly, and there are few pores. The double laser assisted FSW surface shows the best quality, manifested by the fewest trims and rags. The mixing of dissimilar materials is further improved and the joint has good shaping, without obvious defects. Tensile strengths of joints of conventional FSW, single laser assisted FSW and double laser assisted FSW were 238 MPa, 423 MPa and 505 MPa, respectively. Laser assisted FSW has the higher tensile strength, which is attributed to the more complete material mixing and thicker layer of element diffusion. The laser preheating can decrease axial downward pressure of stirring head and radial stress of the stirring needle in the welding process significantly compared with those in conventional frictional stir welding. In particular, double laser preheating can make stresses on the stirring needle more uniform. This is conducive to mutual flowing and integration of dissimilar materials for FSW. Meanwhile, it can reduce the wearing loss between the stirring head and welding component. Double laser preheating can prolong service life of stirring heat significantly and it can improve welding speed significantly under the same rotating speed of the same stirring heat, thus enabling to increase welding efficiency.