Effect of laser interface pretreatment on the microstructure, adhesion strength, and corrosion resistance of PVD-AlTiN coatings on Mg alloy substrates

Abstract

Depositing nitride coatings on Mg alloys is an important pathway for protecting Mg alloy substrates. However, the as-deposited coatings often suffer from numerous growth defects and high residual stress. Nano-textured interfaces enable the conscious alteration of grain growth during coating deposition. While PVD nitride coatings have been explored for Mg alloys, few studies have investigated how nano-texture affects their microstructure, residual stress, and interfacial adhesion. In the present study, we fabricated a novel surface nano-texture: laser-induced periodic surface structures (LIPSS) on AZ31B Mg alloy via ultrafast-laser pretreatment. Subsequently, AlTiN coatings were deposited on both the LIPSS-modified and conventionally polished interfaces using multi-arc ion plating. A combination of microstructural, mechanical, and electrochemical techniques was employed to analyze the resulting changes. It was found that LIPSS-modified interfaces significantly refined the microstructure of the deposited AlTiN coatings, weakened their crystallographic texture, and alleviated their residual stress. The optimization of the coating microstructure is ascribed to the diversified nucleation sites and multidirectional growth of coating grains on the LIPSS-modified interface. Consequently, by introducing this LIPSS-modified interface, the AlTiN coatings achieved notably improved adhesion strength (L_C2 = 34.4 N) and corrosion resistance (I_corr = 2.7 μA cm⁻²), in comparison with the coatings deposited on the conventionally polished interfaces. The enhanced adhesion strength arises from the suppressed crack propagation, which is induced by the alleviated residual stress. The improved corrosion resistance is attributed to the highly dense microstructure of the coating. This work is among the first to comprehensively evaluate the influence of LIPSS nano-textures on AlTiN coating behavior over Mg alloys, and these findings provide a pathway for durable, mechanically robust coatings on reactive lightweight alloys.