3가 크롬 도금욕에서 펄스 도금의 전기화학적 변수 최적화를 통한 크롬 도금막의 내식성 향상 연구

Electroplating chromium films in a trivalent chromium bath has been extensively investigated as a replacement for the conventional hexavalent chromium bath. However, commercialization of the trivalent chromium method has been hindered because the resulting chromium films exhibit inferior mechanical properties compared to hexavalent chromium coated film. In this study, we enhanced the properties of trivalent chromium electroplated film using a pulse-reverse (PR) method. Firstly, the cathodic current density needed to produce a shiny surface was optimized using direct current (DC) electroplating. After optimizing the cathodic current density, the appropriate anodic current density for PR electroplating needed to achieve optimum crack density and corrosion resistance was investigated. The chromium coating prepared using PR electroplating exhibited higher corrosion resistance than that prepared by DC electroplating, because it suppressed crack formation. Concerning the electrochemical corrosion behavior in 3.5 wt% NaCl solution, the optimized sample (PR2) electroplated at an anodic current density of 0.04 A cm-2 showed a corrosion potential shift of 129.9 mV to the anodic direction, and an increase in electrochemical corrosion resistance which was bigger than the chromium film prepared using DC electroplating. This optimization of electrochemical variables opens a new way to obtain improved electrodeposited film with low crack density and high corrosion resistance. (Received May 14, 2019; Accepted August 21, 2019)