A new perspective on the surface quality of titanium alloys in pulsed electrochemical machining: Effect of frequency and passivation film

The main challenge in electrochemical machining (ECM) of titanium alloys is not processing efficiency, but the difficulty in achieving high-quality machined surfaces. Titanium alloys are particularly susceptible to pitting, and there are obvious dissolution differences among different phases in ECM, which greatly affect the machining accuracy and surface quality. This paper aims to eliminate the dissolution disparity between different phases and enhance the surface quality of titanium alloys through the synergistic effect of a similar normal distribution current waveform and passivation film. A new experimental phenomenon was found that the presence of a passivation film resulted in a remarkably smooth pit during the initial pitting stage, with no discernible dissolution differences among different phases. A superior surface quality can be achieved when the surface of the titanium alloy sample is composed of these smooth pits. From this perspective, the effect of frequency and passivation film on pitting process and surface quality of titanium alloys in pulse ECM was systematically investigated. In particular, at the frequency of 100 Hz, high surface quality was achieved on Ti-6.5Al-2Zr-1Mo-1 V (TA15) alloy with a surface roughness of Ra 0.69 μm while the dissolution disparity between different phases was significantly eliminated. The rate of material thickness removal was 0.09 mm/min. Successful applications on other titanium alloys, such as Ti-6Al-4 V (TC4), Ti-25 V-15Cr-0.3Si (Ti40), and Ti-5.8Al-4Sn-3.58Zr-0.7Mo-0.5 Nb-1.1Ta-0.4Si (Ti60), further validated that high-quality surfaces can be obtained with surface roughness values of Ra 0.31 μm, Ra 0.44 μm and Ra 0.92 μm respectively. [Display omitted] •The synergistic effect of current waveform and passivation film improve the surface quality of titanium alloys in ECM.•The current waveform and frequency affect the corrosion morphology and repassivation process.•High quality surfaces of titanium alloys are achieved under optimized frequencies.