Study on the process of thick chromium plating and coating performance from trivalent chromium sulfate electrolyte

A chromium deposit with thickness more than 30 μm was obtained by trivalent chromium plating in sulfate electrolyte.The influences ofρ(Cr3+),ρ(additive),ρ(H 3 BO3),φ(complexant)and pH value on bath's covering power and plating rate,of plating time on plating rate and deposit thickness were studied respectively.The hardness and surface morphology of deposit at different hot treatment temperatures were researched.The optimal process conditions were gained by orthogonal test as follows:144 g/L Na2SO4,50 g/L K2SO4,60～80 g/L H3BO3,15 g/L Cr 3+,10～ 15 mL/L complexant,a suitable amount of wetting agent,pH value of 2.5～3.0,temperature of 40°C,and a current density of 10～15 A/dm2.A semi-bright and silvery white chromium deposit with hardness of 706 HV was gained by the process.The hardness of chromium deposit is up to the maximal value of 1 401 HV after heat treatment at a temperature of 200°C.Deposit quality was affected because of the crack on the surface of deposit caused by the increasing heat treatment temperature.