Investigation of the microstructure an‎d mechanical properties of dissimilar welds of DP590 an‎d HSLA440 automotive steels in the resistance spot welding process

10/22/2026 12:00:00 AM

In this study, the microstructural an‎d mechanical properties of dissimilar resistance spot welding of DP590/HSLA440 steels were investigated with a focus on the effect of welding current an‎d holding time. For this purpose, steel sheets were prepared according to AWS D8.1 stan‎dard an‎d after welding at currents of 7 to 11 kA (with a step of 1 kA) an‎d holding times of 5, 10, 20 an‎d 40 cycles, mechanical an‎d characterization tests were performed. Tensile tests were performed for currents of 7 to 10 kA at a tensile rate of 1 mm/min an‎d hardness tests were performed for currents of 8 an‎d 10 at all four holding times. Also, fracture surface an‎d weld microstructure were examined using scanning electron an‎d optical microscopes. Calculations of equivalent carbon (0.72) an‎d critical temperatures confirmed the possibility of martensite phase formation. Increasing the current an‎d holding time increased the button diameter an‎d decreased the thickness. The microstructure of the weld button was mainly composed of plate martensite, an‎d with increasing current intensity an‎d holding time, its volume fraction increased, an‎d the volume fraction of martensite decreased from the weld to the base metal. On the DP590 side, the supercritical an‎d intercritical regions were mostly martensite, an‎d the subcritical region consisted of tempered martensite. In HSLA440, the supercritical regions were martensite, the intercritical regions were martensite an‎d ferrite, an‎d the subcritical region showed grain growth. The tensile test results showed that the bond strength increased with increasing current an‎d holding time, an‎d its maximum value was obtained at a current of 10 kA. The lowest strength was obtained at a current of 8 kA an‎d a short holding time. A change in the failure mode from IF to PF was also observed with increasing current. Also, with increasing welding current intensity, the softening phenomenon on the HSLA440 side increased, but increasing the holding time reduced this effect. Hardness measurements showed that its value in the weld bead increased with increasing current intensity an‎d holding time, an‎d increased from about 400 Vickers in poor conditions to 470 Vickers in optimal conditions. In both steels, the hardness of the HAZ was lower than that of the weld bead, but the hardness dro‎p was more severe in HSLA440. Examination of the HAZ/WZ interface showed that the fracture often starts from this area, so that the fracture in the HAZ was soft an‎d in the WZ the presence of cleavage surfaces indicated a brittle fracture. Also, the weld pool boundary cracks decreased with increasing current an‎d holding time, but the excessive formation of martensite in some conditions intensified the brittle fracture.

فولاد پيشرفتۀ خودرويي , مُد شكست , فولاد هاي دو فاري , جوشكاري مقاومتي نقطه اي , فولاد هاي كم الياژ استحكام بالا

Advanced High-Strength Steel , Interfacial Failure , Dual-phase steel , Resistance Spot Welding , High-strength low-alloy steel

amirsiyavash mojaver

dr ashiri an‎d dr shabestari