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 electropoli shing Al-7Si-0.3Mg cast alloy. Consideration of the fundamental curren t density-voltage relation and limiting current density has made it po ssible to identify an optimum applied voltage for good electropolishin g through variation of different parameters (electrolyte, bath tempera ture, electrode distance, surface roughness before polishing, cathode material, etc.). The significant findings of the present study are tha t (1) using 30% perchloric acid +20% glycerol moderator +50% methanol electrolyte, (2) maintaining 15 mm electrode distance and a temperatur e of -33 degrees C, and (3) electropolishing the Al-7Si-0.3Mg cast all oy at 15 V for 2 minutes reveal the microstructures clearly. The limit ing current density is about 7 mA/cm(2) for the preceding conditions f or attaining good electropolishing. Electropolishing can also be achie ved under the same conditions even at room temperature (26 degrees C), but the clarity of the microstructure is not as good as that obtained through electropolishing at -33 degrees C. (C) Elsevier Science Inc., 1997.