Preparation of AlTiVNiCu/Cu–Al gradient functional coating via laser cladding for enhanced wear and corrosion resistance of Mg Li alloy

The poor surface properties of MgLi alloys and the excellent comprehensive performance of high-entropy alloy (HEA) coatings are highly complementary. This study uses laser cladding technology to deposit an AlTiVNiCu/Cu–Al gradient functional coating with favourable wear and corrosion properties on MgLi alloy substrates. Through the design of the gradient coating structure, laser cladding is used to coat HEA layers on low-melting-point MgLi alloys, which effectively reduces further dilution of Mg and Li in the substrate. Notably, the Mg content in the prepared AlTiVNiCu protective layer is only 2.34 %. Furthermore, the microstructure, phase structure, microhardness, tribological and corrosion properties of the gradient coating are systematically studied. The protective layer consists of V-rich BCC1, (Ni, Ti)-rich BCC2, Cu-rich FCC, Mg-rich BCC3 and nanoscale β-Ti phases, with a predominance of body-centered cubic (BCC) structural phases. The average microhardness is 547.46 HV0.3. Under a load of 3 N, the average friction coefficient of the protective layer is 0.54, with a wear volume of only 2.87 % compared with that of the substrate, which is satisfactory wear resistance. In a 3.5 wt% NaCl solution, the protective layer exhibits the highest corrosion potential (−0.49 VSCE, where SEC denotes saturated calomel electrode), and the lowest corrosion current density (1.14 × 10−6 A·cm−2), representing a remarkable enhancement compared with those of the substrate (−1.57 VSCE and 5.41 × 10−4 A·cm−2).