Evolution of microstructure and enhanced mechanical properties of dissimilar Al and Mg joints with Cu interlayer fabricated by friction stir welding

The formation of brittle intermetallic compounds (IMCs) poses a challenge to Al/Mg dissimilar alloys FSW. The results of the implemented systematic Cu interlayer experiments show that the diffusion forms of elements in the weld nugget zone (WNZ) and banded structure zone (BSZ) varied at different rotation speeds and Cu interlayer thicknesses. Adding Cu interlayer led to the evolution of conventional aluminium–magnesium IMCs towards aluminium–copper, magnesium–copper, and aluminium–copper–magnesium IMCs. The tensile properties of the joints reached the maximum at lower rotation speeds and thinner interlayer thicknesses, respectively, which was attributable to the generation of Al 2 Cu and Al 2 CuMg with the best compressive and shear resistance, respectively. Simultaneously, the dispersion distribution of Cu elements and phase transition weakened the stress gradient of BSZ.