The aluminum part is immersed in a sulfuric acid bath and connected as the anode. An electric current causes the aluminum surface to form Al₂O₃ (aluminum oxide). The film has two layers: a porous outer layer (can be dyed) and a dense barrier layer. Pore diameter: 10-50nm.
Standard anodizing: 5-20μm, can be dyed. Used for consumer electronics, architectural aluminum. Hard anodizing: 30-100μm, HV350-550. Used for mechanical parts, cylinders. Natural (clear) anodizing: no dye, transparent. Sulfuric anodizing accounts for 90%+ of production.
Organic dyeing: wide color range. Electrolytic coloring: metal salts (tin, nickel, silver) deposited in pores. Sealing is essential — must be done with hot water, steam, or room-temperature sealant. Without sealing, the oxide film absorbs fingerprints and oil.
Foshan (Guangdong): largest aluminum profile anodizing base. Suzhou (Jiangsu): consumer electronics. Ningbo (Zhejiang): cylinder hard anodizing. Linqu (Shandong): architectural profiles. Pricing: standard ¥5-15/kg, dyed ¥8-25/kg, hard anodizing ¥15-50/kg.