The weldability study of carbon nanotube based 2nd generation primer coated steel for automotive applications
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The selection and application of the type coating to steel sheets in automotive industries depend on factors like corrosion protection, manufacturing compatibility and cost. The ‘first generation’ type primer coating improved the corrosion protection of chromate free pretreatments, however it deteriorated the resistance spot weldability of the sheets. The development of 2nd generation primer coating with additives such as CNT showed dominance in corrosion protection properties along with zinc. The present paper investigates the resistance spot weldability of the CNT added primer coating. The weldability was evaluated by comparing the CNT added primer with 1st generation primer for nugget size and electrode life. At lower welding currents, the nugget size of the CNT added primer was significantly lower than the primer coated steels. The increase in the dynamic resistance of the CNT coated steel after nugget formation led to higher nugget sizes at higher currents. The decrease in aluminum and increment in the Fe concentration at the electrode surface during welding of CNT based primer coated steels would improve the electrode life.
KeywordsResistance spot welding Corrosion protection primers Duplex system Organic coating
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