Microstructure and corrosion characteristics of laser-alloyed magnesium alloy AZ91D with Al-Si powder.

Blown-powder laser surface alloying was performed on the magnesium alloy AZ91D with Al-Si alloy powder to improve corrosion resistance. Characterization by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD) analysis revealed that intermetallic compounds (IMCs) of Mg2Si, Al12Mg17 and Al3Mg2 were formed in the matrix of α-Mg and Al solid solutions in Al-Si alloyed layers. The anodic polarization test in 3.5% NaCl aqueous solution showed that preferential corrosion occurred in the α-Mg matrix of the AZ91D base metal. The Al-Si alloyed layers exhibited a lower corrosion rate and a higher polarization resistance than AZ91D. The compactly dispersed dendritic Mg2Si phase, and the dendritic and angular phases of Al12Mg17 and Al3Mg2 in the alloyed microstructure were observed to be corrosion-resistant, constituting a barrier that retards corrosion. Corrosion initiated at the interface between IMCs and the solid solution matrix, and at substructures of the matrix, subsequently pervaded into the surrounding microstructure.