Bobbin tool friction stir welding (BTFSW) technique was applied to a Mg–Zn–Zr alloy ZK60. The results indicated that the plates were joined successfully with no welding defect forming at the investigated processing parameters. BTFSW resulted in significant grain refinement and dissolution of the Mg₄Zn₇ precipitates in the stir zone (SZ). Extensive softening was observed in the SZ because the strengthening resulted from the grain refinement could not compensate the strength loss caused by the precipitates dissolution. The ultimate tensile strength of the joint reached 80.3–84.4% of that of the ZK60 parent metal. All the joints consistently fractured in the SZ adjacent to the thermo-mechanically affected zone (TMAZ) on the advancing side (AS). The extensive softening in the SZ makes it more susceptible to plastic deformation during transverse uniaxial tension, which is the precondition for the failing in the SZ-side. Within the SZ, the profuse activation of {10–12} extension twinning in the SZ-side on the AS (with <0001> crystal direction parallel to transverse direction) and basal slip in the adjacent region (with <0001> crystal direction at ∼45° to transverse direction) caused deformation incompatibility. Additionally, the abrupt change of microstructure from the TMAZ to the SZ aggravated the deformation incompatibility, leading the fracture to initiating in the SZ-side on the AS.

线轴工具搅拌摩擦焊（BTFSW）技术应用于Mg-Zn-Zr合金ZK60。结果表明，在所研究的加工参数下，板材成功连接，没有焊接缺陷形成。BTFSW导致晶粒细化和Mg ₄ Zn _7的溶解在搅拌区（SZ）中沉淀。在SZ中观察到了广泛的软化，因为晶粒细化导致的强化无法弥补沉淀物溶解引起的强度损失。接头的极限抗拉强度达到ZK60母材的80.3–84.4％。在前进侧（AS）的热机械影响区（TMAZ）附近的SZ中，所有关节始终断裂。SZ的广泛软化使其在横向单轴拉伸过程中更容易发生塑性变形，这是SZ侧失效的前提。在SZ内，{10-12}延伸双峰在AS的SZ侧（结晶方向平行于横向的<0001>）的大量激活和邻近区域的基底滑移（<0001> 结晶方向与横向方向成约45°）会导致变形不相容。此外，从TMAZ到SZ的微观结构的突然变化加剧了变形的不相容性，导致断裂发生在AS的SZ侧。