Aluminum plate products are widely used in automobile, construction and other industries, improving the quality of aluminum products is the fundamental survival of enterprises, aluminum material in the air is very unstable, easy to produce with the naked eye is also difficult to identify the oxide film. Due to the different processing methods of aluminum parts, such as casting molding, or directly cut by rolling plate, or mechanical fine processing molding, or after different processing molding and heat treatment or welding, etc. , the surface of the workpiece will show different state, different degree of dirt or trace, so in the pre-treatment process must be based on the actual conditions of the surface of the workpiece to choose the pre-treatment process. In the pre-treatment process, it should be noted that not all the surfaces of the castings are machined, and the unmachined surfaces are retained with thick oxide layers formed in the course of casting, and some of them are also sandwiched with sand layers, at this point should first use machining or sandblasting method to remove this part of the original oxide film, or after the alkaline wash processing, only in this way can both clean the raw part of the oxide layer, and it can avoid the change of tolerance dimension of machining position. Although the natural oxide film on the surface of the workpiece is formed at first, it is easy to remove, but it is greasy and heavy, especially in and around the hole. The workpiece must be cleaned by organic solvent first, if the surface is washed directly with Alkali, it is not only greasy but also can not bear strong alkali corrosion for a long time. The result will affect the coarseness and tolerance of the surface of the work piece.