Abstract The resistance spot welding (RSW) of advanced high strength steel exhibits a high tendency to fail in unfavorable interfacial fracture. To solve this problem, a novel slightly concave electrode was designed. The RSW joints of Q&P steel obtained with the conventional dome-radius electrode and the novel slightly concave electrode in terms of microstructure, micro-hardness and tensile-shear properties were investigated and compared. Numerical simulations were conducted to reveal the thermo-electric field evolution and explain reasons for the improvement of weldability with the slightly concave electrode. The results show that by aid of slightly concave electrode, the welding current range meeting the requirement of button pullout failure was doubled and upper limits on tensile-shear load reached 28.5 kN and achieved 16 % improvement. By the employment of slightly concave electrode, a ring-shaped distribution of current density formed at the initial stage due to the ring-shaped contact interface of electrode/steel, which fabricated an annular nugget. Because of the lower current density and the stronger corona bond zone after the formation of nugget, the slightly concave electrode decreased the possibility of early expulsion, resulting in larger upper limits on nugget and wider welding current range.

中文翻译：

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微凹电极对Q&P1180钢电阻点焊的影响

摘要 先进高强度钢的电阻点焊（RSW）在不利的界面断裂中表现出很高的失败倾向。为了解决这个问题，设计了一种新型的微凹电极。研究和比较了用传统圆顶圆弧焊条和新型微凹焊条获得的 Q&P 钢 RSW 接头的显微组织、显微硬度和拉伸剪切性能。进行了数值模拟以揭示热电场演化并解释使用略微凹入的电极提高可焊性的原因。结果表明，在微凹焊条的辅助下，满足扣件拔出失效要求的焊接电流范围增加了一倍，拉剪载荷上限达到28.5 kN，提高了16%。通过采用微凹电极，由于电极/钢的环形接触界面，在初始阶段形成了环形电流密度分布，从而制造出环形熔核。由于熔核形成后较低的电流密度和较强的电晕结合区，略微凹入的焊条降低了早期排出的可能性，从而导致熔核上限和更宽的焊接电流范围。