Corrosion and Cavitation Erosion Behaviors of Friction Stir Processed Ni-Al Bronze: Effect of Processing Parameters and Position in the Stirred Zone

As-cast Ni-Al bronze (NAB) was subjected to friction stir processing (FSP). Different processing parameters including rotating rate, traverse speed, and processing passes were selected to investigate their effect on the corrosion and cavitation erosion properties. Polarization curve and electrochemical impedance spectroscopy (EIS) were used to reveal the corrosion behavior. Cavitation erosion tests were conducted with an ultrasonic vibration device, and the eroded surfaces were observed using scanning electron microscopy (SEM). Results showed that cavitation erosion resistance was improved for all the processed NAB compared to the as-cast, and a two-pass processed NAB possessed the best corrosion resistance since it had further homogenized microstructure compared to the single-pass processed ones. Corrosion and cavitation erosion tests were also conducted on samples (Surface, Subsurface, Middle, and Bottom) obtained by machining from different positions of the stirred zone (SZ) in a constant-parameter processed NAB along the plate thickness. The Middle was more corrosion resistant since its equiaxed microstructure contributed to a homogeneous oxide film on the surface. The grains in the Bottom were the finest, so the Bottom was the most cavitation erosion resistant.