Experimental study of nanoelectroplating steel spot welding structure under impact tensile-shear loading

The tensile shear fracture behavior of solder joints under impact load influences the whole vehicle’s safety substantially. This paper takes the QP980 steel resistance spot welding (RSW) structure as the research object to study the tensile-shear fracture behavior of the RSW structure under tensile-shear loading. The microstructure observation of the welded spot shows that the metallographic structure is the martensite. The porosity defects in the melting zone are the primary defect reflecting the obvious plate-cracks on both sides of the nugget. The paper demonstrates the Vickers hardness test result of the spot-welded zone. According to the test, the micro-hardness distribution result shows that the higher the martensite, the greater the hardness. A softened zone emerges adjacent to the heat-affected zone on the welded base material interface. The quasi-static and dynamic tensile-shear tests on the QP980 steel RSW lap-joint specimens show that the fracture on the BM is adjacent to the welded spot under quasi-static loading but close to the heat-affected zone under dynamic loading. Under dynamic loading, the weld seam and softened zone of the welded spot have a direct influence on the fracture. On the recovered specimen’s fractured section, there are a large number of apparent dimples on the section of the BM under quasi-static loading and the section of the HAZ under dynamic loading with nucleation, growth, and aggregation of cavitation, resulting in ductile fracture.