Electropolishing of Al-7Si-0.3Mg cast alloy by using perchloric and nitric acid electrolytes

The aim of the present study was to find a good method for electropolishing Al-7Si-0.3Mg cast alloy. Consideration of the fundamental current density-voltage relation and limiting current density has made it possible to identify an optimum applied voltage for good electropolishing through variation of different parameters (electrolyte, bath temperature, electrode distance, surface roughness before polishing, cathode material, etc.). The significant findings of the present study are that (1) using 30% perchloric acid + 20% glycerol moderator + 50% methanol electrolyte, (2) maintaining 15 mm electrode distance and a temperature of −33 °C, and (3) electropolishing the Al-7Si-0.3Mg cast alloy at 15 V for 2 minutes reveal the microstructures clearly. The limiting current density is about 7 mA/cm2 for the preceding conditions for attaining good electropolishing. Electropolishing can also be achieved under the same conditions even at room temperature (26 °C), but the clarity of the microstructure is not as good as that obtained through electropolishing at −33 °C.