Effect of beam oscillating frequency on the microstructure and mechanical properties of dissimilar laser welding of AA2060 and AA6061 alloy

Abstract

Welding of dissimilar aluminum alloys is gaining an attention in academic and industrial communities because of wide spread industrial application. In this study, the dissimilar laser welding of AA2060-T8 and AA6061-T6 thin slabs is conducted using circular mode oscillation welding with amplitude of 0.5 mm and different oscillation frequencies. With the aid of numerical simulation, optical microscopy (OM) and electron backscatter diffraction (EBSD), the microstructure evolution mechanism of the obtained welded joints and their correlations with mechanical properties and failure modes are systematically studied. In comparison to rectilinear weldment, the mechanical properties of welded joint could be significantly improved via beam oscillation welding, with the maximum of tensile strength reaching to 277 MPa at oscillation frequency of 30 HZ, (about 89% of the AA6061-T6 sheets) and the elongation improving by about 65% compared to the sample with non-oscillation welding. Higher frequency dramatically decreases the EQZ area at AA2060 side, and sharply expenses the equiaxed grain zone at central area of welded joints. In EBSD analyses, the orientations of refined columnar grains present randomization tendency, and the coarse ones show solidification texture component with <100> parallel to growth direction. The relationships of these microstructural variations and fracture modes are analyzed. In addition, to fully understand the formation mechanisms of welded microstructures, thermal simulation is conducted in this paper. From results of the thermal simulations, it can be observed that the 30 HZ oscillating weldment has a similar cooling rate with the one of non-oscillation mode, coupled with the stirring effect of beam oscillation, resulting in a refinement of the solidified microstructure and relatively higher mechanical properties.