Effect of plate thickness on mechanical properties and failure behaviors of resistance spot welded advanced high strength steels

Abstract

In this work, the mechanical properties and failure behaviors of resistance spot welds (RSWs) were investigated under lap-shear (LS) loads. Different types (B1500HS, 340/590DP, 420/780DP, DC03 and DC07) and thicknesses (1.0–1.8 mm) of body-in-white steel plates were welded as LS samples. The microstructures, weld defects and Vickers hardness values of different RSW regions were measured to explain the failure mechanisms of RSWs. Obvious hardness reduction near the heat affected zones of RSWs can induce stress concentration and crack initiation. Moreover, with the increment of plate thicknesses, the increasing peak loads (FLS) values and RSW fracture mode translation (from pull-out fracture to partial interfacial fracture) were also identified. The LS load displacement curves were divided into three ranges. The remarkable correlation between the FLS values and the tensile strengths (σb) of base metals (BMs) was found in the secondary range. Based on this, a new introduced parameter, standardized shear strength (σSS), can quantified the relationship between the FLS values, plate thicknesses and BM σb values, σSS = FLS / T1 / T2 = f(σb). Finally, a FLS prediction model was provided for the LS samples with different materials and plate thicknesses.