Mechanical behavior investigation for quenching and partitioning steel dissimilar resistance spot welds

Abstract

Resistance spot welding is still the most common joining process for autobody structure assembly. It has many advantages and is simple to use, but the main challenge is controlling the process parameters that affect mechanical properties and weld quality. Advanced high-strength steels were developed to meet the demands of automakers such as lighter and stronger autobody. Quenching and partitioning (Q&P 980) steel is a third-generation advanced high strength steel with a combination of high strength and high ductility. In this study, effect of resistance spot welding parameters on the mechanical performance of dissimilar combination of Q&P980 steel and SPFC780Y high strength steel was investigated. Welding current, welding time, electrode pressure and holding time were chosen as the most important process parameters influencing the weld quality. A comprehensive investigation was conducted on geometrical attributes such as nugget size, fusion zone width, fusion zone area, electrode indentation and heat affected zone area and their correlations with peak load (Pmax), failure energy, fracture energy, and elongation at peak load (Lmax). In contrast the failure modes and fracture behavior were studied using scanning electron microscopy. It was observed that using high levels of welding current and welding time while maintaining low levels of electrode pressure and holding time result in a maximum peak load, energy absorption and maximum (Lmax) with pullout failure mode (PF) and this was demonstrated for large nugget size to a critical limit. The methods and findings of this research can be used as a basis for further research and development in the field of dissimilar resistance spot welding.

Keywords

• Resistance spot welding
• Dissimilar welding
• Autobody
• Third generation advanced high strength steels
• Failure mode
• Geometric attributes of the weld