The electrochemical polishing behavior of porous austenitic stainless steel (AISI 316L) in phosphoric-sulfuric mixed acids

The electrochemical polishing of porous austenitic stainless steel (PASS), AISI 316L, in the phosphoric-sulfuric mixed acid with volume-ratio of 1 : 1, 2 : 1 and 3 : 1 at temperature ranging from 60 to 80 °C was studied. Electrochemical polishing of PASS was performed in the potential located in the limiting-current plateau of its anodic polarization curve using a rotating cylinder electrode (RCE). The results show that the electrochemical polishing of PASS is strongly affected by the volume ratio of the mixed acid and the polishing temperature, yet very little by the potentiostatic polishing charge. An optimal brightening and leveling surface of PASS could be achieved by polishing in 2 : 1 v/v mixed acid at 70 °C. Whereas, polishing in 1 : 1 and 2 : 1 v/v ratios at and above 75 °C would result in formation of enlarged pores on the PASS surface due to high dissolution rate within the pores. Pores with rounded edges in the surface morphology of PASS was shown when polishing in 3 : 1 v/v mixed acid at temperature ranging from 60 to 80 °C. The effects of temperature, acid volume-ratio as well as potentiostatic polishing charge on polishing behavior were discussed based on the results of electrochemical test and the polished surface morphology using scanning electron microscope (SEM).