A black phosphate coating for C1008 steel

• Published in: Surface & coatings technology Vol. 176; no. 2; pp. 215 - 221
• Main Authors: Li, Guangyu, Niu, Liyuan, Lian, Jianshe, Jiang, Zhonghao
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 2004; Elsevier
• Subjects: Applied sciences; Chemical conversion; Corrosion; Corrosion prevention; Exact sciences and technology; Laser-absorption; Metals. Metallurgy; Nonmetallic coatings; Phosphating; Production techniques; Salt spray; Scanning electron microscopy; Surface treatment; X-ray diffraction; Salt spray; X-ray diffraction; Chemical conversion; Scanning electron microscopy; Phosphating; Laser-absorption; Phosphates; Sodium Molybdates; Salt spray test; Heat treatment; Laser heating; Cast iron; Steel; Experimental study; Corrosion protection; Coatings; X ray diffraction; Surface treatment; Corrosion resistance; Corrosion test; Lubrication
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/S0257-8972(03)00736-9

This paper describes an effective metal finishing technology for obtaining black phosphate coatings on steel. The black conversion coating obtained on steel (C1008, AISI) and cast iron (No.35, ASTM) was dense and uniform with a thickness up to 18 μm. The coating shows better corrosion resistance; lubricating ability and higher efficiency of light-absorption than the traditional phosphate coatings. The black phosphate-forming mechanism was investigated. It is shown that sodium molybdate added to the black phosphate treatment bath can refine the microstructure. Corrosion tests showed that the corrosion rate was lower than that of traditional phosphating. The black phosphate coating, when employed as the pretreatment layer before laser heat-treatment, can remarkably improve the efficiency of light-absorption during laser heat-treatment. This phosphate technology had been employed successfully on the production line in the automobile industry.