Microstructure and interface properties of plasma spray welded high Al bronze coating

High Al bronze coatings were fabricated on the substrate with different thermal conductivities and chemical components by plasma spray welding. The effects of element diffusion between the high Al bronze coatings and substrate on the microstructure and interface properties were studied. The morphologies, phase structures and phase element content of the spray welding coatings, and the interface morphologies and interface diffusion of Fe and Al were investigated by optical microscopy (OM), XRD, SEM and EDS. The interfacial bonding strength between the coatings and substrate was measured by tensile test. The results indicate that Fe in the 45# carbon steel substrate diffuses into the high Al bronze coating, a metallurgical welded interface forms, and interface bonding strength reaches 346.8 MPa. The content of Fe-rich K phase increases, and the hardness of the coating surface reaches 301.3HV. Al in the high Al coating diffuses onto ZQAl9-4 aluminum bronze substrate, and interface bonding strength is obviously improved with the increase of the width of the transition layer. The content of Cu-rich α phase increases, and surface hardness reaches 272.7HV. Due to the high thermal conductivity of T3 copper, little Fe and Al diffuse into T3 copper substrate, and interface bonding strength is the lowest. However, the microstructure of the coating is homogeneous and refined, and the surface hardness is dramatically improved.