Characterization of black chromating: Optimization by experimental scheme

A study was made of the influence of variation of physico-chemical paramete rs of a chromating electrolyte on the properties of chromated layers (resis tance to salt spray and color). This study was carried out using an experim ental scheme. Black chromating layers are very frequently used for the prot ection of galvanized steel parts in the automobile industry. Three types of black chromating processes were investigated, ail carefully chosen: pure z inc, zinc-cobalt and zinc-iron. These processes act differently; a drift of the electrolytes in industry causes some fluctuations on the properties wa nted. The development of techniques of characterization of chromate convers ion film as far as chemical and physical properties are concerned enabled o ptimization of the operating conditions.