Study on Laser Cladding NiAl/Al2O3 Coating on Magnesium Alloy

A NiAl/Al2O3 coating was prepared on an AZ91D Mg alloy substrate by laser cladding of the plasma-sprayed coating. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the phases and to study the morphology, respectively. The adhesion strength and the porosity ratio of the coating material were measured by a tensile testing machine and an optical microscope (OM), respectively. The microhardness was measured using a micro Vickers hardness tester. The results show that after laser cladding metallurgical bonding occurrs at the interface between the NiAl transition layer and the substrate. The adhesion strength of the coating increases from 11.34 to 33.2 MPa. The coating became denser and the porosity ratio decrease from 10.23 % to 4.10 %. The metastable γ-Al2O3 phase in the coating without laser cladding is transformed completely into the stable α-Al2O3 phase. The microhardness HV0.05 is improved from 3290 to 5200 MPa, which is beneficial to the wear resistance.