Metal surface is unavoidably anodized during various kinds of heat treatment, mechanical processing, transporting and keeping process which results in an uneven thickness oxide layer. Meanwhile, it is easily to be polluted by various kinds of oil contamination and absorbing some other impurity. Solvent can be used to clean oil contamination and some absorbing impurity, thinner oxide layer firstly; later use chemical and mechanical treatment or use chemical treatment directly.
For serious oxide metal surface, the oxide layer is very thick so solvent clean and chemical treatment can’t be directly used at this condition but it would be better to proceed mechanical treatment in advance. Usually metal surface after treatment is highly active and more easily to be polluted by dust and moisture once again. Therefore, metal surface after treatment should be cemented ASAP. Maintaining period after different treatment for metals is as below:
（1）Aluminum alloy after wet process sandblasting treatment 72h;
（2）Aluminum alloy after chromic acid- vitriolization 6h;
（3）Aluminum alloy after anodizing 30days;
（4）Stainless steel after vitriolization 20days;
（5）Steel after sandblasting 4h;
（6）Brass after wet process sandblasting treatment 8h
1. Surface treatment methods for aluminum and aluminum alloy
[Method 1] Degrease treatment. Use absorbent cotton bedewing solvent to clean it, after removing oil contamination, use cleaning cotton cloth to clean few times is ok. Common use solvents are: trichloroethylene, acetic ether, acetone, butanone and gasoline etc.
[Method 2] Chemical treatment in following solution after degreasing: after soaking 10-30min in concentrated sulfuric acid 27.3, potassium dichromate 7.5, water 65.2 at 60-65°C; take out them and clean by water; dry or fire them at 80°C; or washing in following solution before drying: phosphoric acid 10, n-butyl alcohol 3, water 20; this method is suitable for phenolic aldehyde-nylon rubber etc and can get good result.
[Method 3] Chemical treatment in following solution after degreasing: after soaking 4.5-6min in ammonium bifluoride 3-3.5, chromic oxide 20-26, sodium phosphate 2-2.5, concentrated sulfuric acid 50-60, boric acid 0.4-0.6, water 1000 at 25-40°C, then water washing and dry it. This method has strong cementing intensity. Within 4h after treatment to cement, it is suitable for cementing between epoxy rubber and epoxy nitrile rubber.
[Method 4] Chemical treatment in following solution after degreasing: after soaking 10-15min in phosphoric acid 7.5, chromic oxide 7.5 alcohol 5.0 formaldehyde （36-38）80 at 15-30°C,then water washing and dry it at 60-80°C.
[Method 5] Anodizing treatment in following solution after degreasing: after soaking 10-15min in concentrated sulfuric acid 22g/1 at 1-1.5A/dm2 DC strength; then soaking 5-20min in saturated potassium dichromate solution at 95-100°C and water washing& dry it.
[Method 6] Chemical treatment in following solution after degreasing: after soaking 10min in potassium dichromate 66, sulfuric acid （96）666,water 1000 at 70°C; and then water washing& dry it.
[Method 7] Chemical treatment in following solution after degreasing: after soaking 3s in nitric acid（d=1.41）3,hydrofluoric acid （42）1 at 20°C, and immediately wash it using cold water; then using hot water at 65°C, distilled water washing and then dry it. This method is suitable for aluminum casting alloy which contains high ingredient of copper.
[Method 8] Anodizing in following solution after sandblasting or polishing: after soaking 10min in chromic oxide 100, sulfuric acid 0.2, sodium chloride 0.2 at 40°C to increase voltage from 0V to 10V and keep 20min;then increase it from 10V to 50V within 5min and keep 5 min; and water washing and dry it at 700°C. Note: dissociative chromic oxide density can’t exceed 30-35g/l.
[Method 9] Chemical treatment in following solution after degreasing: after soaking 5min in sodium silicate 10, nonionic detergent 0.1 at 65°C; then water washing below 65°C; using distilled water to wash and dry it. This method is suitable for aluminum foil cementing.
[Method 10] Chemical treatment in following solution after degreasing: after soaking 1min in sodium fluoride 1, concentrated nitric acid 15, water 84 at room temperature; treatment in following solution after washing: after soaking 1 min in concentrated sulfuric acid 30, potassium dichromate 7.5, water 62.5 at room temperature, then wash and dry it.
2. Surface treatment methods for magnesium and magnesium alloy
[Method 1] Degrease treatment. Common use solvents are: trichloroethylene, acetic ether, acetone, acetic ether and butanone.
[Method 2] Soaking 5min in following solution after degreasing at 70-75°C: sodium hydroxide 12, water 100; using cold water to wash; then Soaking 5min in following solution at 20°C: chromic oxide 10, water 100, anhydrous sodium sulfate 2.8; using cold water to wash, then using distilled water to wash and dry it at 40°C.
[Method 3] Soaking 10min in sodium hydroxide 6.3 solution after degreasing at 70°C; after washing, soaking 5min in following solution at 55°C: chromic oxide 13.8, calcium sulfate 1.2, water 85; using distilled water to wash before soaking 3min in following solution at 55°C: chromic oxide 10, sodium sulfate 0.5, water 89.5; then wash and dry it below 60°C.
[Method 4] Soaking 3min in following solution at 20°C: chromic oxide 16.6, sodium nitrate 20, glacial acetic acid 105, water 100; using cold water washing, clean it by distilled water and dry it below 40°C.
[Method 5] Soaking 3min in following solution at 60-70°C: sodium dichromate 10, magnesium sulfate 5, manganese sulfate 5, water 80; using cold water washing, clean it by distilled water and dry it below 70°C.
[Method 6] Soaking 20min in following boiling solution after degreasing: sodium dichromate 1.5, ammonium sulfate 3, ammonia water(d=0.88)0.3, water 93.7; using hot water washing, clean it by distilled water and dry it.
[Method 7] Anodizing in fluorine hydrogenated amine 10 solution below 30°C to make current density lower than 0.45A/m2(one pole panel) and AC voltage 90-120V; then wash and dry it.
[Method 8] Anodizing in following solution at 20-30°C: potassium hydroxide 12, aluminum 0.75, anhydrous potassium fluoride 3.4, sodium phosphate 3.4, potassium permanganate 1.5, water 80 at 85V AC voltage, current density 1.1-1.4A/m2; and then clean by cold distilled water and dry it.
[Method 9] Soaking 5-15min in following alkali liquor after degreasing at 70°C: sodium hydroxide 23-34, water 400, washing 5min in cold water and then soaking 5-15min in following solution at 55°C: chromic oxide 57-68, calcium nitrate 5, water 450, washing 2min in cold water and then soaking 3-12min in following solution at 55°C: chromic oxide 45, sodium phosphate 8, water 450, washing 2min in cold water and then dry it for 30min below 40°C.
