LAUSR

AISI 4340, a high strength low alloy steel employed in aeronautical structural components, are always protected by various surface treatments from failure. In order to obtain better mechanical properties and corrosion resistance economically, in this study, multiple surface treatments were applied to the AISI 4340 steel, including of nickel-cadmium duplex electroplating, chromate conversion processing, and solid solution treatments with different temperatures and duration times. To evaluate the properties of the nickel-cadmium duplex coating for various solid solution treated AISI 4340 steel, thickness and hardness measurements, salt spray tests, XRD and SEM inspections were performed. The experimental results showed that the electroplated specimens, followed by 300~350°C solid solution treatment, exhibited a distinct nickel-cadmium intermediate compound (Cd5Ni). The highest hardness reached was HV0.3 582.9 after 300°C solid solution treatment for 120 min. Moreover, the anti-salt corrosion capability of the nickel-cadmium layers effectively improved with the 300~325°C solid solution treatment. However, the mechanical properties and corrosion resistance declined with the increase in temperature above 350°C because of the depletion of the cadmium layer and Cd5Ni compound, and the formation of cadmium oxide and chloride. [doi:10.2320/matertrans.M2017282]