Improvement of surface resistance to cavitation corrosion of nickel aluminum bronze by electropulsing-assisted ultrasonic surface rolling process

A surface process electropulsing-assisted ultrasonic surface rolling process (EP-USRP) has been used to treat nickel aluminum bronzes (NAB). Surface quality, hardness and corrosion resistance were evaluated to analyze the surface resistance to cavitation corrosion. The surface roughness was reduced from turning Ra 0.733 μm to EP-USRP Ra 0.050 μm, eliminating the surface turning furrow and improving the surface quality. The surface hardness of the sample treated by EP-USRP at 15 V was increased from 160 HV to 267 HV, and a hardness gradient layer of more than 1000 μm was obtained, thereby improving the surface strength. As the electric pulse which promotes the proliferation and movement of dislocations, the surface strength increased first and then decreased. EP-USRP acts on the surface layer of the lamellar phases to deflect and shred, and tend to be parallel to the surface, which will change the crack propagation path, so that the cracks tend to expand parallel to the surface. Moreover, the samples treated by EP-USRP showed superior corrosion resistance than untreated ones. The surface weight loss of the samples after EP-USRP was greatly reduced compared with the turning surface. The EP-USRP makes NAB the greater surface quality, the stronger surface layer, the higher corrosion resistance and the deflection of lamellar phases is the main reason for the improvement of the surface cavitation corrosion resistance.