Al coatings were prepared by twin wires arc spraying process on P355NL1 steel substrate, and the as-sprayed Al coatings were annealed at different temperatures. The effect of annealing temperature on phase composition, morphology and element diffusion was investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS). The results show that small pores and many droplets on the surface of the coating gradually disappear with increasing annealing temperature. Meanwhile, Cr can diffuse to the top surface of coating at 900 degrees C. The thickness of the diffusion layer at the interface increases from 6 to 113 mu m when the annealing temperature increases from 600 degrees C to 900 degrees C. The coating annealed at 700 degrees C is composed of a single phase of Fe2Al5. The coatings annealed at 800 degrees C and 900 degrees C become porous and loosen. Besides Fe2Al5, Al phase, Fe3Al phase, and Cr-Al-Si intermetallic compound form at the interface of substrate and coating at 700 degrees C. For the coatings annealed at 800 degrees C and 900 degrees C, the compounds at the interface between coating and P355NL1 substrate become more complicated, and more ternary compounds form. The coatings have a relatively perfect structure when the annealing temperature is 700-800 degrees C.
