Study on the Part Unit Corrosion Evaluation for Automotive Lower Arm Using Electrochemical Cyclic Corrosion Test

摘要

This research focused on the development of the part unit evaluation for an organic coated automotive lower arm using the electrochemical cyclic corrosion test (E-CCT). The E-CCT accelerates both the coating degradation and the perforation corrosion. The applied potential for the coating degradation was determined to be -500 mV(SCE) for anodic polarization and -900 mV(SCE) for cathodic polarization. The applied current for the perforation corrosion was equivalent to the applied anodic potential. The E-CCT was conducted for the duration of 8 cycles, which is considered to be equivalent to 4 years of driving. After the E-CCT, the coating degradation was evaluated by electrochemical impedance spectroscopy (EIS) measurements. Especially, the Z(100) (mHz) value (impedance value at a frequency of 100 mHz) of the part unit represented the amount of corrosion damage of the lower arm parts. The Z(100) (mHz) of the degraded coating area had a decisive effect on the Z(100) (mHz), value of the entire lower arm. This result was caused by electrochemical interaction between the non-degraded coating area and degraded coating area. The non-degraded coating area and the degraded coating area of the lower arm formed the parallel circuit which provides a satisfactory result.