Abstract
This paper presents the effects of double pulse resistance spot welding (RSW) on the microstructural evolution, elemental distribution and mechanical properties of a 3rd generation 1 GPa advanced high strength steel (AHSS). In order to investigate the effect of double pulsing, the steel was exposed to single and various double pulse RSW schedules. The first current pulse was applied to create the weld nugget, while the second current pulse generated a secondary weld nugget and annealed or (partial) re-melted the primary weld nugget, depending on the magnitude of the current. The effect of the second current pulse on the weld nugget and heat-affected zone characteristics was investigated using optical microscopy and electron probe microanalysis (EPMA). Optical and electron microscopy revealed that the secondary weld nugget is fully martensitic, showing a typical solidification microstructure, while the annealed zone reveals an equi-axed martensitic structure. EPMA results showed that elemental segregation has been considerably reduced in the annealed zone. Mechanical properties of the welds show that the AHSS studied is prone to weld metal failure for single pulse RSW. However, the double pulse RSW method can lead to significantly improved mechanical performance and favourable failure modes.
Highlights
The demand for the development of lighter, safer, greener and more cost-effective vehicles leads to continued development of advanced high strength steels (AHSSs) that meet functional requirements on strength and formability that allow weight reduction and provide good crashworthiness for automotive applications
This paper presents the effects of double pulse resistance spot welding (RSW) on the microstructural evolution, elemental distribution and mechanical properties of a 3rd generation 1 GPa advanced high strength steel (AHSS)
Quantitative elemental distributions at the weld edges of resistance spot welds were determined by electron probe microanalysis (EPMA)
Summary
The demand for the development of lighter, safer, greener and more cost-effective vehicles leads to continued development of advanced high strength steels (AHSSs) that meet functional requirements on strength and formability that allow weight reduction and provide good crashworthiness for automotive applications. In these steels, the required properties are achieved by means of multi-phase microstructures [1]. The presence of a relatively high percentage of alloying elements in combination with the high cooling rates of the welding process leads to the formation of a martensitic microstructure that influences the mechanical properties of the welds. Apart from the martensite, the segregation of the alloying elements and inclusions are
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