Laser surface remelting of plasma-sprayed nanostructured Al ₂O₃-13 wt%TiO₂ coatings on magnesium alloy

Plasma-sprayed nanostructured coatings were successfully deposited on an AZ91D magnesium alloy substrate using the as-prepared nanostructured Al ₂O₃-13 wt%TiO₂ feedstock and were subsequently remelted by a CO₂ laser. The effects of laser remelting on the microstructure, phase composition and mechanical properties of the ceramic coatings were investigated by scanning electron microscope, X-ray diffractometer and Vickers microhardness tester. The results indicate that the laser remelted coatings exhibit excellent metallurgical bonding to the substrate. Pores and lamellae structures in the as-sprayed coatings have been effectively eliminated and a more compact and homogenous microstructure is achieved after laser remelting. The metastable γ-Al₂O₃ phase in the as-sprayed coatings was transformed to stable α-Al₂O ₃ during laser remelting. The microhardness of the remelted coatings was enhanced to 1000-1500 HV_0.3, which is about 15 times higher than that of the substrate. In addition, with the decrease of laser scanning speeds, the microhardness was increased correspondingly.