Aluminum plate products are widely used in automotive, construction and other industries. Improving the quality of aluminum products is the foundation of the company's survival. Aluminum materials are extremely unstable in the air, and it is easy to produce oxide films that are difficult to identify with the naked eye. Due to the different processing methods of aluminum parts, such as casting molding, or directly cutting from the rolled sheet, or mechanical fine processing, or after different processes, heat treatment or welding, the surface of the workpiece will be presented. Different states, different degrees of dirt or traces, for this reason, in the pre-treatment process, the pre-treatment process must be selected according to the actual situation of the workpiece surface. It is necessary to pay attention to the pretreatment process. Not all surfaces of the cast molded parts are machined. The unmachined surface is left with an excessively thick oxide layer formed during the casting process, and some are also covered with a sand layer. The processing or sand blasting method first removes the original oxide film of this part, or after alkali washing, and only processes the original oxide layer of the unprocessed part, and avoids the change of the tolerance dimension of the machined part. The problem that the fine processing parts need to pay attention to in the pre-treatment process: although the natural oxide film on the surface is formed at the beginning, it is easy to remove, but the oil is heavy, especially in and around the hole, such workpiece must first pass through the organic solvent. Cleaning, if directly washed with alkali is not only greasy and difficult to remove, and the fine processing surface can not withstand long-term alkali corrosion, the result will also affect the roughness of the workpiece surface and the tolerance of the fit, and may eventually become a waste.