Development of requirements for resistance spot welding dual-phase (DP600) steels. Part 1: the causes of interfacial fracture

Sie sind hier: Homepage > Suche

Development of requirements for resistance spot welding dual-phase (DP600) steels. Part 1: the causes of interfacial fracture

Marya, M. / Gayden, X.Q.

The resistance spot welding of two galvanized DP600 steels with 1.8 and 2.0-mm sheet thickness was investigated to enhance the understanding of weld fracture during a well-established automotive quality control test. The effects of several process parameters (including weld current, weld time, and weld force) on zinc expulsion, mechanical properties, defects, and microstructures of resistance spot welds were all studied in relation with the two major types of weld fracture (i.e., interfacial and button pullout). It was established that the slight differences in chemical composition and galvanized coating between the two selected DP600 steels affected negligibly weld microstructures, and were of no measurable consequences to weld fracture. In contrast, the difference of 10% for their sheet thickness was responsible for smaller weld diameters, lower weld tensile-shear forces, larger shrinkage voids, and more frequent interfacial fractures in welds from the thicker DP600 steel. For the two steels, occurrence of weld interfacial fracture was eliminated using long weld times (>20 cycles), low currents (<9 kA), and high forces (>900 lb, or 4.0 kN); i.e., process parameters that increased weld diameters while preventing zinc ingestion into the fusion zone. The effect of zinc was most prominent in welds that were made abnormally fast (e.g., ~5 cycles), where both solidification cracking and a change in type of weld fracture were found due to interdendritic low-melting point constituents. (to be continued)