Microstructures and Salt Spray Corrosion Behavior of a Laser Thermal Sprayed Al Coating on a S355 Steel Substrate
D-H. Zhang, J. Zhang, B-X. Yan and D-J. Kong
An Al coating was sprayed on S355 steel with the laser thermal spraying (LTS) process using a Nd:YAG laser. The morphologies, chemical elements, and phase compositions of the obtained LTS Al coating were analysed using a field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS), and X-ray diffractometer (XRD), respectively. The residual stress of the Nd:YAG laser thermal sprayed Al coating was measured using an XRD stress tester. The effects of LTS on the salt spray corrosion (SSC) of the Al coating are discussed using a SSC test regime and the electrochemical performance of Al coating was also analysed. The results show that the Fe in the S355 steel was diffused into the Nd:YAG laser thermal sprayed Al coating, the intermetallic compound of Fe–Al is formed at the coating interface. The residual stress of the Nd:YAG laser thermal sprayed Al coating enhances its corrosion resistance. The Al oxides are generated on the Al coating, which hinders the corrosion ions into the Al coating and further improves its corrosion resistance. The passivation zone of Al coating shifts positively, indicating that the Al coating on the S355 steel has better corrosion resistance.
Keywords: Nd:YAG laser, S355 steel, Al coating, laser thermal spraying (LTS), microstructure, residual stress, corrosion resistance