Effect of Al Content on the Microstructure and Corrosion Resistance of Low-Pressure Cold-Sprayed Fe-Al Coatings

Using low-pressure cold spray technique, Fe-Al composite coatings with different Al contents were applied to the surface of 45 steel to improve its corrosion resistance in chloride-containing settings. The microstructure, mechanical characteristics, and electrochemical corrosion behavior of the coatings were thoroughly examined in relation to the Al content (2, 4, 6, and 8 wt.%). The findings show that the microhardness of the composite coating decreases monotonically (from 157.98 HV to 99.29 HV) as the Al content rises because of the increased proportion of the soft phase; in contrast, the porosity and corrosion current density show a pattern of first decreasing and then increasing. The coating porosity was reduced to a minimum (1.37%) when the Al concentration reached 6 wt.% because the soft Al particles experienced enough plastic flow to fill the holes in the hard Fe matrix. The 6Al composite coating demonstrated the best electrochemical protection performance in a 3.5 wt.% NaCl solution, with the lowest corrosion current density (2.237 × 10−4 A/cm2) and the strongest interfacial charge transfer resistance. The synergistic corrosion protection mechanism comprising significantly densified physical shielding and microgalvanic sacrificial anode protection by the active Al phase was clarified in this study. The ideal composition ratio for this system was determined to be 6 wt.% Al by carefully matching the coating’s mechanical load-bearing needs with long-term corrosion prevention goals.