Design and characterization of in-situ TiB reinforced TiB/Ti50Zr25Al15Cu10 non-equiatomic medium-entropy alloy composite coating on magnesium alloy by laser cladding

The improvement of corrosion resistance and wear resistance levels is of great significance because of the farranging impacts of them on the further application of magnesium alloys. In this work, a novel TiB/Ti50Zr25Al15Cu10 medium-entropy alloy composite coating (MEACC) was successfully prepared on the surface of magnesium alloy by laser cladding. The effect of LaB6 content on microstructure, micro-hardness, wear resistance and corrosion resistance of Ti50Zr25Al15Cu10 coatings was studied in detail. The results show that TiB/Ti50Zr25Al15Cu10 MEACCs are mainly composed of alpha-Ti, BCC and TiB phases. With LaB6 content increased, the microstructure of the coating is refined and homogenized. And when the addition amount is excessive, Cu2La clusters appear. The lattice distortion caused by La3+ with large ion radius leading to the formation of hard BCC solid solution, as well as the dispersion strengthening of TiB in-situ, the coating presents high micro-hardness and excellent wear resistance. Especially, the average micro-hardness values of Ti50Zr25Al15Cu10 coating with 4 wt% LaB6 is similar to 679.4 HV0.3, which is about 11 times than that of the substrate (similar to 61.6 HV0.3). Besides, TiB/Ti50Zr25Al15Cu10 MEACC displays excellent corrosion resistance. The minimum corrosion current density is 8.52 x 10(-7) A center dot cm(-2), and the oxidation phenomenon emerged in the coating. The oxide film is mainly composed of the oxidation state of Ti, Zr, Al, Cu and the sub-oxide state of Cu.