Before the aluminum alloy sheet is formed and completed, the surface of the sheet needs to be pretreated to facilitate the processing of it later. Pretreatment includes 5 steps.
- Degreasing treatment: The purpose is to remove the lubricant and other dirt on the surface of the prodsuct, in order to ensure that in the alkali washing process, the surface corrosion of the prodsuct is uniform, in order to improve the quality of oxidation prodsucts. Degreasing treatment is generally used with a concentration of 5-25% sulfuric acid, degreasing temperature of 60-80c.
- Etching treatment: its purpose is to further remove the dirt on the surface of the prodsuct, and the prodsuct surface thickness of about 25-1000A natural oxide film removed, so that the base metal surface exposed, in order to facilitate the smooth progress of oxidation and coloring, generally using 40-80 degrees NaOH solution.
- Pickling treatment: the purpose is to remove the black corrosion prodsucts remaining on the surface of the prodsuct after corrosion, in order to obtain a bright metal surface.
- Matting treatment: the purpose is to make aluminum or aluminum prodsucts without luster on the surface so that the formation of non-glossy surface after anodic oxidation treatment, the formation of spot corrosion, generally using 20-40c ammonium fluoride solution.
- Polishing treatment: in order to eliminate mechanical damage and corrosion spots on the surface of aluminum prodsucts, improve the surface smoothness and gloss depth generally to polishing treatment.