Removing loose oxide layer and producing dense α-phase layer simultaneously to improve corrosion resistance of Ti-6Al-4V titanium alloy by coupling electrical pulse and ultrasonic treatment

Abstract

The loose oxide layer on the surface of Ti-6Al-4V titanium alloy can be removed and a dense α-phase layer with the thickness of 11 μm can be produced simultaneously by coupling electrical pulse and ultrasonic treatment (CEPUT). In addition, after CEPUT, the surface grain is refined, the surface roughness is reduced to 0.529 μm, and the surface hardness reaches to 627 HV, showing significant gradient change. During the CEPUT, the processability of the α-phase oxygen-rich layer is improved by the electroplasticity of high peak currents, and the α-phase oxygen-rich layer produces large plastic deformation. Most of the α-phase oxygen-rich layer is removed after the CEPUT, and the remaining coarse α-phase grains are refined to form a dense α-phase layer. The corrosion resistance of the dense oxide layer on the surface has been studied. The results show that the self-corrosion current density of the sample in the NaCl solution decreases to −8.4922E-08 A/cm2 after CEPUT. Compared with the untreated sample, the self-corrosion current density is reduced by two orders of magnitude. The reason for the increased corrosion resistance of titanium alloys may be that the electrolyte is blocked by the dense and intact α-phase layer on the surface and cannot penetrate further into the titanium alloy.