Microstructure and properties of in-situ synthesized ZrC-Al3Zr reinforced composite coating on AZ91D magnesium alloy by laser cladding

In-situ synthesized ZrC-Al3Zr reinforced composite coatings were fabricated on AZ91D magnesium alloy with a mixture of Al, Zr and B4C powders by laser cladding. Granular ZrC reinforced phase was synthesized in all 10 wt %, 20 wt% and 30 wt% (Zr + B4C) coatings, while Al3Zr with rod-like morphology was found only in the two latter coatings. Al3Zr was replaced by Al9.83Zr0.17 at the content of 10 wt% (Zr + B4C) because of relatively low content of Zr. The size of most ZrC and Al3Zr was < 3 mu m. Al12Mg17, alpha-Mg, AlB2 and Al3Mg2 were also detected at the composite coatings. The syntheses of ceramic phase and some intermetallic compounds increased the hardness of the coating. The maximum hardness value (346 HV) was obtained at the coating with 30 wt% (Zr + B4C), which was 5 times higher than that of the substrate. The composite coatings also had better wear resistance than AZ91D substrate and the friction coefficient of the coatings decreased with the increase of (Zr + B4C) content. Polarization curves indicated that the composite coatings were harder to corrode than the substrate.