| 摘要 |
PURPOSE:To obtain a multiply coated steel material having superior heat and corrosion resistances by successively coating the surface of a steel material with a Zn-Ni alloy layer by electroplating, a black Ni layer by electroplating and a chromate film. CONSTITUTION:The surface 1' of a steel material 1 is pretreated by degreasing and derusting, and a Zn-Ni alloy layer 2 is formed on the surface 1' by electroplating. The Ni content of the layer 2 is regulated to about 7-15wt%. A black Ni layer 3 is formed on the surface 2' of the layer 2. The Zn content of the layer 3 is regulated to about 30-50wt%. The plated steel material 1 is then immersed in an aqueous soln. of chromic acid anhydride for about 20-60sec, and it is taken out, wached, and dried at ordinary temp. - about 150 deg.C. The immersing, washing and drying stages are carried out once or more to form a chromate film 4 on the surface 3' of the layer 3. |
