Simulations and Experiments on the Microstructure and Property Evolution of In Situ TiC+Al3Ti-Reinforced Aluminum Coatings on AZ91D Magnesium Alloy

Abstract

With the development of computational thermodynamics, it is possible to design a material based on its simulated microstructure and properties before practical operations. In order to improve the surface properties of AZ91D magnesium alloy, Jmatpro was used in this study to design an alloy system with in situ TiC+AlTi3-reinforced aluminum coatings. The Gibbs free energy, hardness, and phase diagrams of aluminum coatings with different ratios of Ti to B4C were simulated. According to the simulation results, TiB2, TiC, Al3Ti_DO22, and Al4C3 were formed in the coating while TiB2, TiC, Al3Ti_DO22, Al4C3, and Al3Mg2 were formed in the transition zone between the base metal and the coating. Based on the simulation results, different amounts of Ti were used with B4C (the ratios were 3:1, 4:1, 5:1, and 6:1) to fabricate TiC+Al3Ti reinforced aluminum coatings on AZ91D magnesium alloy via laser cladding. The microstructure and phase composition of the coating were studied using scanning electron microscopy (SEM) incorporated with energy- dispersive spectrometry (EDS) and X-ray diffraction (XRD). The results indicated that intermetallic phases, such as AlTi3(C, N)0.6, AlMg, Al3Mg2, Al3Ti, and TiC were formed in the coatings. As the Ti content increased, the content of Al3Ti increased and the content of TiC decreased in the coatings, which is consistent with the simulation results. The average hardness of the coatings was approximately four to five times that of the magnesium alloy substrate, and the corrosion current density of the coatings was around 2.5 × 10−6, which is two orders of magnitude lower than that of AZ91D magnesium alloy.