Study on strength and plasticity of modulated laser welds in dissimilar joints of CHP30 die-cast aluminum alloy

An experimental investigation was conducted on the issues of high porosity, elemental segregation, and insufficient joint strength-ductility encountered during laser welding of dissimilar aluminum alloys CHP30 (high-pressure die-cast, HPDC) and 6D10 (wrought). The influences of continuous wave (CW) and modulated laser welding processes on weld defects, microstructure, and mechanical properties were comparatively analyzed. The results demonstrate that the modulated laser process, which induces periodic melt pool oscillation via dynamic heat input, significantly reduced porosity from 3.19% to 0.91%. Concurrently, the secondary dendrite arm spacing (SDAS) was refined from 11.0 μm to 6.8 μm, and the equiaxed grain zone (EGZ) width was expanded by 86%, reaching 1200 μm. Attributed to the exceptionally low porosity and substantially enhanced EGZ width, the tensile strength and elongation after fracture of the modulated laser joint were measured at 254 MPa (equivalent to 95.1% of the base metal strength) and 4.7%, respectively. This represents a 30.3% increase in tensile strength and 262% improvement in elongation compared with the CW laser joint.