Aluminum Alkaline Electrolytic Polishing Process

In this paper, the Aluminium's electro-polishing was studied in details by using the D.C and constant voltage,D.C and pulse current, cycly-reversed current respectively,the machanism of Aluminium's alkaline electro-polishing was analysised by the anodic polarization and A.C-impedance experiments.The main subjects are as follow:1. Factors affecting the electro-polishing were discussed,a new additive was obtained which offers several advantages over traditional electro-polishing technology such as low working temperature, long life solution and high surface reflectivity. The results show that the optimized condition for D.C and constant voltage electro-polishing is:CNaOH:16g/L, CPEG:28ml/L, CNa2C03:30g/L, CST:8g/L, CrrNiSg/L, Voltage:6.5V, Temperature:50"C, Stiring speed:3-5r/s.During experimenting,it was found by accident that under some condition,the Aluminium has nice surface after electro-polishing by using the glucose as additive.2. The feasibility of D.C and pulse electro-polishing was investigated.lt indicates that this technology has several defects such as high operating voltage, slow smoothing speed and great Aluminium wastage.3. By using cycly-reversed electro-polishing, several additives were investi-gated,some factors were discussed,and the optimized parameters were obtained:(Wllg/L, CartAilOg/L, C. d:14~16A/dm2, Working ratio:90%, Vposmv/Vnegative=15V/10V, Frequency: 1.2Hz, Temperature:40'C, Time:18~20min. Compared with the traditional alkaline electro-polishing,this cycly-reversed electro-polishing technology possess favorable advantages with a potential for industrial use:the surface has good metal luster;the reflectivity can reach 90%;the solution life is prolonged almost two times;the temperature can reduce to 40癈;and the working condition can be improved, So the cost can be greatly cut down.4. It's concluded that during the alkaline electro-polishing,the anode is passivated by a special oxidation film which allows ions to pass through. Accordingly, a new mechanism was put forward that during electro-polishing,there are two processes atthe same time:smoothing and brighting.The metal surface is smoothed by the adsorbing layer whose thickness is different on the protrude and on the concavity;the metal luster is obtained by suppressing the crystallographic electro-chemical dissolution, because the controlling step is ion diffusing through the oxidation film.Based on this theory,some phenomena which appeared during electro-polishing can be successfully explained.