Laser cladding of AZ91D magnesium alloy with Ni-Si-Mg

AZ91D Magnesium alloy was laser cladded with Ni-Si-Mg to enhance the surface hardness. The microstructures and phases of the cladded zone were characterized by optical microscope (OM), scanning electron microscope (SEM), and X-ray diffractometer (XRD). The micro-hardness could be improved up to a maximum of 500-550 Hv in Ni64.82Mg9.41Si25.77 (at.%) and 650-700 Hv in Ni70.83Mg6.27Si22.9 (at.%) as compared to 80 Hv of the as-received substrate. The high micro-hardness of the Ni-Si-Mg coating is due to a microstructure consisting mainly of Ni₃Si, Ni₃₁Si₁₂ and Ni₁₆Mg₆Si₇. With the increase of Mg content from 6.27 to 9.41, the diffraction peak intensities of Ni₁₆Mg₆Si₇ and Ni₃₁Si₁₂ decreased, while the diffraction intensity of Ni₃Si increased.