Effect of Laser Remelting of Fe-Based Thermally Sprayed Coating on AZ91 Magnesium Alloy on Its Structural and Tribological Properties

An Fe-based coating was thermally sprayed onto the surface of AZ91 magnesium alloy via the High-Velocity-Oxygen-Fuel (HVOF) method. The thermally sprayed coating with a thickness of 530 ± 25 µm and a porosity of 0.7 ± 0.1% did not show any macrostructural defects and did not cause any degradation of the AZ91 alloy. Laser remelting of the surface layer of the sprayed coating resulted in the recrystallization of the structure and the disappearance of presented pores, splat boundaries, and other defects. This led to an increase in the hardness of the remelted layer from the original 535 ± 20 HV0.3 up to 625 ± 5 HV0.3. However, during the laser remelting at a laser power of 1000 W, stress cracking in the coating occurred. The tribological properties were evaluated by the ball-on-plate method under dry conditions. Compared to the uncoated AZ91 magnesium alloy, a higher value of friction coefficient (COF) was measured for the as-sprayed coating. However, there was a decrease in wear rate and weight loss. The remelting of the surface layer of the as-sprayed coating led to a further decrease in the wear rate and weight loss. Based on the obtained data, it has been shown that the application of laser-remelted thermally sprayed Fe-based coatings on AZ91 Mg alloy improves hardness and tribological properties compared to bare Mg alloy and as-sprayed Fe-based coatings.