铝质质料在空气中是极不稳定的，容易生成用肉眼也难以识别的氧化膜。由于大连数控加工铝件加工工艺要领的差别，如铸造成型，或是由延压板材直接剪切而成，或是机械精细加工成型，或是经差别工艺成型后又经热处理或焊接等，工件外貌都会泛起差别状态，差别水平的污物或痕迹，为此在前处理工序中必须凭据工件外貌的实际情况选择前处理的工艺要领。

Aluminum materials are extremely unstable in air and are prone to forming oxide films that are difficult to identify with the naked eye. Due to the different processing methods of aluminum parts in Dalian CNC machining, such as casting molding, direct cutting from extruded sheet metal, mechanical fine processing molding, or forming through different processes and then heat treatment or welding, the surface of the workpiece will present different states and degrees of dirt or marks. Therefore, in the pre-treatment process, the pre-treatment method must be selected according to the actual situation of the workpiece surface.