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Quasi-static tensile shear mechanical properties of resistance spot welds of three dual phase (DP) grades including DP600, DP780 and DP980 are investigated. Results showed that weld fusion zone size, failure mode and the strength/ductility of failure location are the main factors governing the peak load and the energy absorption of spot welds. Heat affected zone (HAZ) softening plays an important role in mechanical properties of DP steels with higher volume fraction of martensite (i.e. DP780 and DP980). It was shown that the peak load of the spot welds is not proportionally correlated to the tensile strength of the base metal. Pronounced HAZ softening in DP980 resulted in reducing its tendency to fail in interfacial failure mode in comparison to DP780. In addition, despite its lower base metal ductility, DP980 weld exhibits enhanced ductility and energy absorption than DP780 due to its pronounced HAZ softening.
Pouranvari et al. (Mon,) studied this question.