Study Of Dissimilar Metal Al/Ti Laser Welding

Based on the laser penetration brazing process (LPB), a CW Slab CO2 laser with an output power of 3.5kW is used to join aluminium and titanium with a thickness of 3mm. The laser acts on the surface of Al alloy, and the melted aluminium wets the interface of titanium to form a brazing joint. Influence of different processing parameters on the width of the seam, Wb/Wt and area of the seam are studied by changing welding speed, beam spot offset, defocusing distance and deflexion angle. Besides, the organization of the joint based on LPB, the interface and the influence of different processing parameters on mechanical property of the joint are also studied.When adequate process parameters are chosen, the seam with good appearance and metallurgical bonding are achieved. Because there are great differences of physical appearance, when the temperature of interface is too high, parts of Ti alloy will melt and go into the seam to format intermetallic compound which have a oversize thickness. Meanwhile, some incomplete fusion phenomenon in the seam was found during analyze. It is found that incomplete fusion phenomenon can be avoided by slowing the weld speed and reducing the incomplete fusion phenomenon. In addition, the incomplete fusion rate can be reduced by taking appropriate defocusing distance and deflexion angle.During analyzing by metallographic microscope, SEM and XRD, it is found that the organizations of the seams are tiny equiaxed crystal when welding speed is lower; the organizations of the seams are tinier dendritic crystal. The intermetallic compound layers are observed in the interface between Ti and weld obviously. The thickness of intermetallic compound on the top and bottom seam are smaller than the mid of the seam, and the largest thickness of seam is less than 2 micron. Al element and Ti element diffuse well in the reacting zone, and no component rapid drawdown happens. The intermetallic compounds are Al2Ti, Al3Ti mostly. Tensile test are carried out to evaluate the mechanical property after welding experiment, and the gained highest strength of the tension is 217MPa.The dissimilar couple between Al and Ti alloys are joined successfully by laser penetration brazing process. The thickness of the intermetallic compound can be controlled, the incomplete fusion phenomenon can be solved, and the mechanical property of the seam can be increased by optimizing the processing parameters.