Abstract
<p>Increased use of advanced high strength steels (AHSS) in resistance spot welding is necessary for manufacturing safe and affordable vehicles. A significant body of work has been completed to document the resistance spot weldability of AHSS. However, In automotive applications, the dissimilar material combinations are very common In automotive construction. There is no literature regarding the resistance spot welding of dissimilar materials DP600 and HSLA350 steels. The objective of this study was to investigate the weldability and mechanical properties of resistance spot welds between HSLA350 and DP600 steels. The dissimilar material spot weld performance was different than the similar material spot welds in each of the HSLA350 and DP600 steels and exhibited different heat affected zone hardness. The DP600 weld properties played a dominating role on the microstructure and mechanical properties of the dissimilar material spot welds. However, the fatigue performance of the dissimilar welds was similar to that of the HSLA welds. Fatigue tests on the dissimilar materials spot welds showed that at a given stress amplitude the 5.5 mm diameter nugget exhibited higher fatigue strength than the 7. 5 mm diameter nugget.</p>
Highlights
Advanced high strength steels (AHSS) have been used in the automotive industry for weight reduction, safety improvements and cost saving
One of the challenges in adopting AHSS is that the higher alloy content required to obtain the bi-phase microstructure promotes increased hardenability in the fusion zone (FZ) and heat-affected zone (HAZ) where high cooling rates are encountered during the weld thermal cycle, influencing the mechanical and metallurgical properties of the spot welded areas and heat affected zones
This is due to the fact that austenitizing was incomplete in the HAZ and even when austenite grains formed, grain growth was restricted by the formation of martensite and bainite and because of the thermal cycles [50-52]
Summary
Advanced high strength steels (AHSS) have been used in the automotive industry for weight reduction, safety improvements and cost saving. One of the challenges in adopting AHSS is that the higher alloy content required to obtain the bi-phase microstructure promotes increased hardenability in the fusion zone (FZ) and heat-affected zone (HAZ) where high cooling rates are encountered during the weld thermal cycle, influencing the mechanical and metallurgical properties of the spot welded areas and heat affected zones. The investigation of these changes is very important for the safety and performance of the welded joints
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