Abstract Three 6061-T6 aluminum sheets with a thickness of 1 mm for each were subjected to the flat friction stir spot welding technique, which contains two steps of welding process. In step 1, a specially designed back plate with a pre-drilled dent was used in order to form a protuberance on the bottom side of the joint. In step 2, the keyhole and the protuberance were removed by using a probe-less rotating tool and a smooth back plate. The optimized welding condition for the three sheet spot welding was 700 kg/550 rpm/2 s in step 1 and 1000 kg/600 rpm/2 s in step 2. Two sheet/sheet interfaces were formed in the bowl-like stir zone. The stir zone showed a grain size varied from 4.2 to 8.6 μm, much smaller than the 17.6 μm of the base metal. Three different tensile test modes were used to evaluate the failure behavior of the joints. The interface between the top and middle sheet showed a longer bonding length of 11.5 mm and a higher fracture load of about 6438 N. While the interface between the middle and the bottom sheet showed a bonding length of 5.2 mm and a fracture load of about 4450 N. The step 2 joints showed plug-type failure mode during the shear tensile tests.

中文翻译：

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三块6061-T6铝板平面摩擦搅拌点焊

摘要 对三块厚度为1 mm的6061-T6铝板进行平面搅拌摩擦点焊技术，包括两步焊接工艺。在步骤 1 中，使用带有预钻孔凹痕的专门设计的背板，以便在接头的底部形成一个突起。在步骤 2 中，使用无探针旋转工具和光滑的背板去除钥匙孔和突起。三个板点焊的优化焊接条件是步骤 1 中的 700 kg/550 rpm/2 s 和步骤 2 中的 1000 kg/600 rpm/2 s。在碗状搅拌区形成两个板/板界面。搅拌区的晶粒尺寸从 4.2 到 8.6 μm 不等，远小于母材的 17.6 μm。使用三种不同的拉伸测试模式来评估接头的失效行为。