A novel hybrid forming process integrating friction stir welding pre-bonding and hot extrusion for fabrication of Mg/Al laminated composites

In this study, multi-layered Mg/Al laminated composites were successfully fabricated using a combination of friction stir welding (FSW) pre-bonding and hot extrusion. The effects of initial stacking sequence (Mg-over-Al and Al-over-Mg) during FSW on interfacial microstructure evolution and mechanical properties were systematically investigated. Microstructure characterization indicated that the Mg/Al layers were primarily composed of fine and uniform equiaxed grains. The stacking sequence had a minimal effect on the texture intensity, grain size, and recrystallization degrees. However, the Mg-over-Al pre-bonding induced significant interfacial metal mixing, leading to the formation of Mg-Al intermetallic compounds (IMCs) inside the plate. In contrast, the Al-over-Mg stacking effectively confined IMCs formation. Mechanical testing results indicated that Al-over-Mg specimen exhibited superior comprehensive mechanical properties (yield strength (YS): 157 MPa, ultimate tensile strength (UTS): 250 MPa, elongation (EL): 9.1 %) compared to the Mg-over-Al configuration (YS:168 MPa, UTS: 183 MPa, EL: 3.4 %). The inferior ductility and strength of the latter were attributed to Mg-Al IMCs at the interface, which initiated cracks and caused premature failure. The marked strength-ductility trade-off highlights the critical influence of the stacking sequence on interfacial IMCs formation and mechanical performance.