Abstract: A layer of TiAl₃ intermetallic compound coating was prepared on Ti6Al4V alloy by hot-dip aluminizing,and the obtained sample was treated by thermal diffusion.The coating was analyzed by XRD and SEM to probe into its structure and compositions.The formation mechanism of the coating was also discussed.The results show that after hot-dip aluminizing at 750℃ for 5 min,a coating consisting of pure Al and TiAl₃ alloy(with thickness of 1.5 μm) is formed on the surface of Ti6Al4V alloy;after annealing at 550℃ for 5 h,the thickness of dense TiAl₃ increases to 40 μm and Al layer almost disappears;after annealing at 930℃ for 5 h,all the coating is composed of pure TiAl₃,but lots of holes appear in the coating at the same time.From the coating surface to the alloy matrix,the amounts of holes are in gradient variation.