中文摘要：

采用无匙孔搅拌摩擦焊对DP6 00镀锌钢和A Z 3 1镁合金进行点焊搭接试验,利用扫描电镜观察其微 观组织,分析拉伸断口推断其断裂过程.结果表明：镁-钢接头成形受转速与轴肩下压量影响敏感,可施焊 工艺参数窗口小;在最优工艺参数下,接头成形良好,镁和钢相互嵌入锁合充分明显,具有典型“机械连 接”特征;接头宏观形貌上,镁和钢分别呈多构状互相嵌入对方并呈涡流状缠绕在-起;微观形貌上,由于 搅拌针直接穿过钢板,钢侧搅拌针作用部分区域被撕裂与搅碎,镁、钢层叠交错分布,流向性明显,并存在 少量由于镁蒸发造成的微观孔洞;拉断试验中,镁、钢分离起始于搅拌区外围不存在机械连接作用的区域, 直至裂纹扩展至焊核区镁、钢互相缠绕部分钢的裂纹处,沿裂纹发生撕裂将钢板从镁板上剥离,断后在钢板 的搅拌区域形成较大孔洞;接头横截面显微硬度显示,无论镁层钢层,其硬度分布均呈“ W”型,符合普遍 搅拌摩擦焊接头硬度分布特征.

英文摘要：

Lap joints tests between dissimilar AZ31 magnesium alloy and DP600 steel sheets were made by friction stir keyholeless welding （ FSKSW） . Scanning electron microscope （SEM） was used to investigate the microstructure and tensile fracture of joints. The experimental results showed that the joint formation is sensitive to the rotation speed of the tool and the vertical descent of the shoulder that results to the small range of welding process parameter. Under the optimum process parameters, the joint formation is good and the interlocking of Mg - steel is obvious with a typical mechanical connection feature. From the macro - morphology of the sample, it can be seen that Mg - steel are hooked into each other, they intertwine together like a vortex. From the micro - morphology, there exists a number of gaps and cracks at the tool function area beside steel side owing to the tool directly going through the steel plate; magnesium -steel appears a layering distribution with obvious flow direction. Meanwhile there is a small amount of micro - pores due to the evaporation of magnesium element. In the tensile test, separation of magnesium - steel starts from the periphery of the mixing zone where the mechanical connection does not exist and the crack continues to extend to the nugget zone where magnesium - steel are intertwined with each other. Steel plate is stripped from the magnesium plate along the crack with the formation of large holes at the mixing zone of steel plate. The microhardness of the samples shows that the hardness distribution of magnesium side or steel side is ＂ W＂ type, which is consistent with the general distribution of friction stir welded joints.