Laser surface remelting of plasma-sprayed nanostructured Al 2O 3–13 wt%TiO 2 coatings on magnesium alloy

Abstract

Plasma-sprayed nanostructured coatings were successfully deposited on an AZ91D magnesium alloy substrate using the as-prepared nanostructured Al 2O 3–13 wt%TiO 2 feedstock and were subsequently remelted by a CO 2 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-Al 2O 3 phase in the as-sprayed coatings was transformed to stable α-Al 2O 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.