Composite plating of hard chromium on aluminum substrate

The paper reports work on the study of the effects of temperature, current density and time on thickness of nickel, copper and hard chromium coatings produced by a multiple electroplating process. Within the ranges of the experimental temperature and current density for all of the nickel, copper and chromium electroplatings, a maximum in the coating thickness as a function of temperature or current density exists. The optimized plating conditions to obtain the thickest coatings are at 2.5 A/dm2 and 49 °C for nickel, 0.8 A/dm2 and 20 °C for hydroxyl ethydene diphosphate (HEDP) copper, 2.6 A/dm2 and 30 °C for acid copper and 29 A/dm2 and 54 °C for hard chromium. Under the optimized conditions, a sound adhesion between any plated materials over the aluminum base is achieved, and a bright, uniform and flawless chromium coating is obtained with a microhardness of HV1029. The hard chromium coating layer has a higher anti-pitting property in 3.5 wt.% sodium chloride solution than that of a 0.1% C–13% Cr stainless steel.