A Pilot Scale Evaluation of a Trivalent Chromium Plating Process

Summary

The evaluation of a decorative chromium plating process based on trivalent chromic chloride is described. The bath utilizes dimethylformamide in the electrolyte solvent. Deposits are microdiscontinuous over decorative thicknesses and plating efficiencies of 30–40% based on trivalent chromium can be obtained over a wide plating range. Commercial zinc diecastings and mild steel pressings have been plated, with adequate coverage of significant faces and metal distribution in general slightly superior to that from proprietary hexavalent solutions. Plating speeds of better than × 0·25 μm (0·000010in) per minute at 13 A/dm² (120 A/ft²) were obtained. Analytical methods have been devised to evaluate the effects of departure from optimum electrolyte composition and corrective measures have been established. Dragout losses have been estimated and the tolerance of the bath to foreign metal contaminants assessed. Static exposure tests have indicated that the deposit performs in a similar manner to other microdiscontinuous systems and confirm earlier accelerated test results.