Microstructure and mechanical properties of dissimilar ZL114A cast and 5A06 wrought Aluminum Alloys joined by electron beam welding

This study investigates the microstructure and mechanical properties of joints between ZL114A cast and 5A06 wrought aluminum alloys fabricated by electron beam welding (EBW). A comparative analysis was performed on three configurations: the homogeneous 5A06-5A06 (5-5) and ZL114A-ZL114A (Z-Z) joints, and the dissimilar 5A06-ZL114A (5-Z) joint, using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), microhardness testing, and tensile testing. The results indicate that the weld zone (WZ) of the dissimilar 5-Z joint exhibited a refined microstructure composed of fine dendrites, interdendritic Mg 2 Si, and eutectic Si phases resulting from elemental mixing. Notably, liquation cracking was observed in the partially melted zone (PMZ) on the 5A06 side. The 5-Z joint displayed a pronounced increase in hardness, with the WZ microhardness peaking at approximately 115 HV, significantly higher than either base metal (≈90 HV for 5A06, ≈65 HV for ZL114A). Conversely, the 5-5 joint softened, while the Z-Z joint hardened relative to their respective base materials. However, due to the formation of brittle phases and crack initiation, the 5-Z joint exhibited the poorest ductility (2.88 % elongation) and a low ultimate tensile strength (244 MPa), a characteristic of brittle fracture. This premature failure is attributed to the synergistic effect of brittle phase formation in the WZ and crack initiation at the heterogeneous interface, establishing a clear relationship between the complex microstructural evolution and the final joint performance.