采用双轴肩搅拌摩擦焊(BTFSW)技术对7.8 mm厚6061-T6铝合金进行了焊接, 对焊接接头各部分的微观组织和截面显微硬度进行了分析, 并对母材和焊核在3.5%NaCl溶液中的腐蚀电化学行为和腐蚀产物膜进行了研究. 结果表明, BTFSW后焊缝表面质量良好, 热-机影响区晶粒发生再结晶和塑性变形, 部分再结晶晶粒发生了伸长和弯曲; 热影响区的部分晶粒在热循环的作用下发生粗化, 焊核呈细小的等轴晶组织; 焊接接头中前进侧热-机影响区硬度最低; 在3.5%NaCl溶液中, 6061-T6铝合金的极化曲线表现为阳极溶解和点蚀, 母材和焊核区的电化学阻抗谱均由容抗弧和感抗弧组成, BTFSW后6061铝合金的腐蚀电流降低; 浸泡480 h后, 呈疖状腐蚀的特征, 腐蚀产物为Al(OH)₃和Al₂O₃. BTFSW可提高6061-T6铝合金的耐蚀性.

Friction stir welding (FSW) is a new solid-state joining method which offers several advantages compared with conventional welding methods, including better mechanical properties, lower residual stress and reduced occurrence of defects. It has already been used for joining Al alloys in the aerospace and automotive industries. In spite of the advantages, FSW also has drawbacks, such as the risk of root flaws in single-side welds. Using a bobbin tool instead is a promising way to solve this problem since the root region is avoided. Compared with standard (single-side) FSW techniques, the bobbin tool FSW has an extra shoulder attached to the tip of the probe, namely the lower shoulder. This setup makes BTFSW capable of joining closed profiles like hollow extrusions. Furthermore, root flaws, such as lack of penetration, which occasionally occurred in standard FSWtechiques, can be completely avoided. In this work, 6061-T6 aluminum alloy was welded by using bobbin tool friction stir weld (BTFSW). The influence of BTFSW on the microstructure development and hardness distribution in the weldment has been investigated. The corrosion behaviors of the base metal and weld nugget in 3.5%NaCl (mass fraction) solution were investigated using SEM, XRD and electrochemical measurements. The results showed that the weld surface of 6061-T6 welded by BTFSW is of good quality. No welding defect was detected in the joints. Three microstructural zones, i.e., nugget zone, thermo-mechanically affected zone, and heat affected zone were discernible. The microstructural analysis indicates that the weld nugget region exhibited fine and equiaxed grain structure with an average grain size of ~8 μm, indicating the occurrence of dynamic recrystallization due to severe plastic deformation and thermal exposure. The thermo-mechanically affected zone underwent plastic deformation and recrystallization occured in this zone due to deformation strain and thermal input. The low hardness zone, determined by constructing the hardness distribution profile on cross-section of joint, located at thermo-mechanically affected zone of advancing side. Although 6061-T6 alloys are readily weldable, they suffered from severe softening in the heat affected zone because of the dissolution of Mg₂Si precipitates during the weld thermal cycle. BTFSW can improve the corrosion resistance of 6061-T6 aluminum alloy in 3.5%NaCl solution. The corrosion behavior results showed that both anodic dissolution and pitting were observed after the immersion test due to the inhomogeneous microstructure of 6061-T6 aluminum alloy. The corrosion products mainly composed of Al(OH)₃ and Al₂O₃. Furthermore, the corrosion process and mechanism were also discussed.