ABSTRACT 1.2 mm thick DP1180 advanced ultra-high-strength steel were successfully friction stir spot welded (FSSWed) with additional water cooling. No hook defect and obvious keyhole were observed in the spot joints when using a specially designed WC-Co tool. Softening of the heat-affected zone was substantially suppressed and the lap shear strength of the joints was obviously enhanced via water cooling. The enhanced strength of water-cooled joints was attributed to the grain refinement, the formation of the untempered martensite and the effective restraint of tool softening underwater. Accordingly, the maximum lap shear strength of 17.9 kN was obtained for the water-cooled joint. This study provides a novel strategy to enhance the strength of the FSSW joints for high-strength steels.

中文翻译：

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附加水冷提高搅拌摩擦点焊先进超高强钢的力学性能

摘要 1.2 毫米厚的 DP1180 高级超高强度钢通过附加水冷成功进行搅拌摩擦点焊 (FSSWed)。使用专门设计的 WC-Co 工具时，在点接缝处没有观察到钩状缺陷和明显的锁孔。通过水冷，热影响区软化得到明显抑制，接头搭接剪切强度明显提高。水冷接头强度的提高归因于晶粒细化、未回火马氏体的形成以及对水下刀具软化的有效抑制。因此，水冷接头的最大搭接剪切强度为 17.9 kN。这项研究提供了一种提高高强度钢 FSSW 接头强度的新策略。