Microstructures and properties in surface layers of Mg-6Zn-1Ca magnesium alloy laser-clad with Al-Si powders

Laser surface cladding with Al-Si powders was applied to a Mg-6Zn-1Ca magnesium alloy to improve its surface properties. The microstructure, phase components and chemical compositions of the laser-clad layer were analyzed by using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results show that the clad layer mainly consists of α-Mg, Mg₂Si dendrites, Mg₁₇Al₁₂ and Al₃Mg₂ phases. Owing to the formation of Mg₂Si, Mg₁₇Al₁₂ and Al₃Mg₂ intermetallic compounds in the melted region and grain refinement, the microhardness of the clad layer (HV_0.025 310) is about 5 times higher than that of the substrate (HV_0.025 54). Besides, corrosion tests in the NaCl (3.5%, mass fraction) water solution show that the corrosion potential is increased from –1574.6 mV for the untreated sample to –128.7 mV for the laser-clad sample, while the corrosion current density is reduced from 170.1 to 6.7 µA/cm². These results reveal that improved corrosion resistance and increased hardness of the Mg-6Zn-1Ca alloy can be both achieved after laser cladding with Al-Si powders.