Formation of electrical contact through an Alodine coating

In some airplane applications, cadmium plated connectors are mounted to Alodine coated aluminum brackets. Good electrical bonding or grounding is essential through the resistive Alodine coating. The Alodine film is a chromate conversion coating applied to protect aluminum against corrosion. A great deal of variability and increase with time is characteristic for the contact resistance at the interface between the cadmium-plated connector and bracket. Significant rework is sometimes required to stabilize the bond. An understanding of the phenomena responsible for the value of the contact resistance between a cadmium-plated connector and an Alodine coated bracket was the goal of this research work. In this research work, scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX) were used to examine the microstructure of virgin Alodine coatings on unassembled brackets. The next set of SEM and EDX examinations was conducted on Alodine coated brackets that had been assembled and disassembled with a connector.