Corrosion Behavior of Bare & Organic Coated ADC-12 Used for Heat Sink Enclosure of on-Board Charger

The automotive sector trend is moving towards vehicle electrification that provides great energy and environmental implications. However, Electrical Vehicles (EVs) are facing challenges in term of charging, driving range and life cycle with respect to existing vehicles. One of the key components in EV which is responsible for charging is On-Board Charger (OBC). OBCs are mainly used in converting DC power from battery pack to AC power and contains different power-electronic devices such as MOSFETs, diodes, magnetics etc. Heat-sinks are used to transfer the heat generated by these electronics and also as an enclosure to accommodate the electronics. Aluminum based alloy-ADC-12 generally used for manufacturing of OBC-enclosure due to its light weight, easy castability and good thermal conductivity. Although ADC-12 aluminum alloy has high corrosion resistance, specific environment condition or situation may accelerate corrosion with extended storage in rainy and salty environments. Normally, mounting position of OBC in vehicle is generally below powertrain system either parallel or tilted to ground surface. Due to this during rainy season there are chances of prolonged water accumulation at fins of ADC-12 enclosure which results into corrosion of ADC-12. Thus, to protect OBC-enclosure from corrosion, organic (Acrylic resin with Al₂O₃ / TiO₂ pigments) coating through Cathodic Electro Deposition (CED) process has been developed and comparative evaluation of corrosion resistance of coated and bare ADC-12 has been studied in this work. Corrosion rate was measured by performing immersion test in 3.5 wt. % NaCl solution for 500 hours. Visual inspection, SEM-EDS analysis and weight loss measurement was used to compare the performance of coated and bare samples after immersion test. Uniform corrosion was observed in case of bare-ADC-12 while negligible corrosion was observed in case of coated samples after immersion test of 500 hours. SEM-EDS analysis indicates the localized corrosion initiated from the intermetallic (rich in Si and Mn, Fe, Cu) and formed their oxides. At exposed region initially Al forms protective alumina (Al₂O₃) layer but after certain time cracking of layer occurs and further corrosion takes place. Corrosion rate by weight loss technique measurement show that bare ADC-12 enclosure corroded approximate three times faster than coated-samples.