Aluminum material in the air is extremely unstable, easy to produce with the naked eye also difficult to recognize the oxide film. Due to the different method of aluminum processing technology, such as casting molding, or directly by the delay of pressure plate shear, or fine mechanical processing and forming, or approved by different process forming after the heat treatment or welding, the surface will present different status, different degrees of dirt or marks, therefore in pre-treatment process must choose according to the actual situation of the surface pretreatment process method. Attention should be paid in the pretreatment process: although the natural oxidation film on the surface of the fine workpiece is just formed, the overthick oxidation layer formed in the casting process remains on the unmachined surface, and the workpiece forms a layer of oily and sintered coking matter before it is transferred to the heat treatment or welding process. The treatment precautions are as follows:

(1) fine processing parts need to be aware of problems in the pre-treatment process: fine machined part while natural oxide film on the surface of the first generation, clear more easily, but the fat, especially in the hole and the surrounding (due to the need of lubrication in the process of machining and add), these artifacts must first by the organic solvent cleaning, if with alkaline cleaning greasy weight is difficult to remove all, not only directly and precision machining surface cannot afford the alkali corrosion for a long period of time, the result will also affect the surface roughness and tolerance to cooperate, zui eventually may become a waste.

(2) problems needing attention in the pretreatment process of casting parts. As not all surface after machining, casting without machining surface with a thick oxide layer formed in the casting process of, some still clip with sand, at this time should be first with machining or sand blasting method, first remove the parts of the original oxide film, or after caustic washing processing again, only in this way can not only remove all unprocessed parts of the original oxidation layer, and can avoid machining parts of tolerance size change.

(3) after heat treatment or welding process of the workpiece before processing need to be aware of the problem: according to the technological requirements, artifacts into heat treatment or subject to organic solvent cleaning before welding process, free surface oil, but now can't do it, so form a layer of oil on sintering of coking on the surface of workpiece, this layer of coking content in organic solvents is difficult to remove all, if soaked in lye can cause local corrosion, pitting or cause uneven, seriously affecting the quality of the product. With the method of concentrated nitric acid immersion to soft this layer of coking, coking soft and then in the lye slightly cleaning can be thoroughly removed.