The effect of pH adjustment of trivalent chromium electrolyte on coating quality

pH value plays an important role in trivalent chromium electroplating. The research is devoted to the investigation of different ways to adjust pH value in the electrolyte. The results indicate that pH value in the electrolyte decreases with time and decreases aggressively during electroplating by adding KOH without any other operation. In microstructure observation, there are many hydrogen pinholes in the coating surface. By reheat the solution after adding KOH, the pH value in electrolyte remains unchanged and changes slightly during electroplating. Number of hydrogen pinholes decreases at the same time. According to Hull cell test, quality range would decrease as reheating time prolonged. The purpose of adjust pH value could be achieve without adding KOH by change the complexing agent from formic acid into ammonium formate. When using ammonium formate, pH value remains unchanged and changes slightly during electroplating, too. The coating appears brightless, with no hydrogen pinhole and rough surface microstructure.