[Other] The Effect of Laser Oscillation Frequency on the Microstructure and Properties of a Novel Low-Density Aluminum Alloy in Laser-Cold Metal Transfer Hybrid Welded Joints Copy

The oscillation frequency of the laser plays a significant role in determining the formation quality, grain structure, and mechanical properties of laser-CMT hybrid welded joints in high-magnesium aluminum alloys. Oscillating laser technology is employed to mitigate welding defects, optimize the weld microstructure, and enhance the mechanical performance of these alloys. In this study, laser oscillation frequencies of 0, 100, 150, 200, and 250 Hz were investigated. The microstructure of the welded joints was analyzed using Transmission Electron Microscopy (TEM) and Electron Backscatter Diffraction (EBSD). The precipitated phases included the alpha-Al matrix phase and secondary phases, such as Mg2Si and MgZn2. At 0 Hz, the weld formation was suboptimal, characterized by severe defects and coarse grain structures. Increasing the oscillation frequency initially resulted in grain refinement, but further increases led to grain coarsening. The smallest grain size and the highest fraction of equiaxed grains were observed at 200 Hz. At this frequency, the volume fraction of Sigma 3 grain boundaries was also at its highest. The oscillating laser effectively suppressed columnar grain growth and promoted grain refinement in this region. The mechanical properties of the welded joint exhibited a trend of first increasing and then decreasing with rising oscillation frequencies. At 0 Hz, the tensile strength of the welded joint was only 215.84 MPa, while at 200 Hz, the mechanical properties were optimized, reaching 324.85 MPa. Swing laser welding optimizes weld microstructure and enhances the mechanical properties of welded joints.