Weldability and mechanical properties of similar and dissimilar resistance spot welds of three-layer advanced high strength steels

Abstract

Similar and dissimilar combinations of a 1000 MPa galvanised dual phase (DP) steel, a 980 MPa transformation induced plasticity (TRIP) steel and a 980 MPa twinning induced plasticity (TWIP) steel were resistance spot welded under different welding parameters. The macrostructure, splash situation, nugget size and mechanical properties of the spot welds were evaluated systematically. The results showed that the different heat conductivities, melting points and surface electric resistances of the DP, TRIP and TWIP steels resulted in the asymmetric weld nuggets of the dissimilar spot welds and the increase in the splash occurring current in order of DP/DP/DP, TRIP/DP/TWIP, TWIP/TRIP/DP, TRIP/TWIP/DP (TRIP/TRIP/TRIP), TWIP/TRIP/DP and TWIP/TWIP/TWIP. For the dissimilar spot welding of galvanised DP1000, uncoated TRIP980 and uncoated TWIP980, the TRIP/TWIP/DP combination can obtain better weld quality than the TRIP/DP/TWIP and TWIP/TRIP/DP combinations.