LOAD CARRYING CAPACITY AND MICROSTRUCTURE OF RESISTANCE SPOT WELDED DUAL-PHASE (DP600) STEEL

摘要

Resistance spot welding is the dominant sheet metal joining method in automotive industry. Dual-phase (DP600) steel sheet of 2.8 mm thickness was spot welded using welding currents up to10 kA, welding holding times up to 100 cycles and using an electrode diameter of 10 mm under constant applied pressure. The microstructure, visual, tensile shear and hardness testing for joints of as-welded and heat-treated samples were investigated. The maximum tensile shear load increases with increasing the heat input which leads to increase the weld nugget size. Consequently, the maximum shear load increases from 11.8 kN to 28.2 kN for a weld nugget size of 5.4 and 10.4 mm, respectively. A slight increase in the hardness value was observed in the weld nugget produced using a shorter welding time or a lower current value. Post-weld tempering for times of 0.5 and 3 hrs has led to a slight increase of the maximum tensile shear load, which could be related to the formation of some precipitates.