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Analyses of Nugget and Expulsion Formation Process during Resistance Spot Welding between Aluminum Alloy and Steel

In this paper, nugget growth stages during resistance spot welding between aluminum alloy and steel, such as surface breakdown, asperity softening, temperature rising, molten nugget formation, nugget growth and mechanical collapse, was analyzed according to resistance dynamic variation during welding. The effects of work pieces surface condition and electrode force on the occurrence of inter-expulsion and surface expulsion was discussed during resistance spot welding.