Effect of Al₂Gd on microstructure and properties of laser clad Mg–Al–Gd coatings

Highlights: • Mg–Al–Gd coatings with different Gd contents were fabricated by fiber laser cladding. • Chemical compositions and crystal structures of the second phases were characterized. • Dispersion of Al₂Gd led to further grain refining and elevated mechanical properties. • Al₂Gd improved high-temperature performances by preventing tiny liquation. - Abstract: In order to investigate the effects of Gd addition on the microstructures and properties of magnesium coatings, the Mg–7.5Al–xGd (x = 0, 2.5, 5.0 and 7.5 wt.%) coatings on cast magnesium alloy were fabricated by laser cladding with wire feeding. The results indicated that the gadolinium (Gd) addition led to the formation of a cubic Al₂Gd phase as well as suppressed the precipitation of eutectic Mg₁₇Al₁₂ phase. The laser clad coating containing nominally 7.5 wt.% Gd presented the highest microhardness, ultimate tensile strength and yield strength at both room temperature and high temperatures. The enhancement of heat resistant capacities was chiefly attributed to the existence of thermally stable Al₂Gd particles, which prevented tiny liquation of eutectic phases along the grain boundaries and made great contributions on maintaining high yield ratio during high-temperature deformation