Automobile aluminum plate needs passivation. After passivation, the naturally formed oxide film and oil stain on the surface of aluminum parts will be removed, and a dense oxide film will be wrapped on the surface of the workpiece through the chemical reaction between aluminum alloy and acidic solution.

After stamping, the oxide film, greasy welding and gluing on the surface of aluminum parts will have an impact. In order to improve the adhesion between the adhesive and the weld, it is necessary to maintain the long-term adhesive bonding and resistance stability of the surface through chemical processes to achieve better welding. Therefore, all parts that need laser brazing, cold metal transition welding (CMT) and other welding need to be passivated by water washing.