6063铝合金搅拌摩擦焊焊缝组织特征与腐蚀行为研究

Microstructure and Corrosion Behavior of Friction Stir Welding Seam of 6063 Aluminum Alloy

研究了主轴旋转速度对6063铝合金板搅拌摩擦焊(FSW)焊缝组织与耐蚀性的影响,采用静态失重法、动电位极化曲线和交流阻抗谱对比研究了母材和焊缝在3.5%的NaCl溶液中的电化学行为,借助光学显微镜和扫描电镜观察母材和焊缝的显微组织以及腐蚀形貌。结果表明,搅拌摩擦焊后,合金焊接接头由母材区(BMZ),热机械影响区(TAMZ),焊核区(WN)组成。晶粒形状由母材区的粗大多边形或长条状转变为焊核区细小的等轴状,在热机械影响区形成了明显的塑性流动现象;母材和焊缝的平均腐蚀速率分别为0.078 1、0.231 5、0.347 2和0.405 1g/(m2·h);6063铝合金的主要腐蚀类型是点蚀和晶间腐蚀,在搅拌摩擦焊过程中晶粒细化和晶界增多是焊缝耐蚀性能降低的主要原因。

The effects of tool rotation speed on microstructure and corrosion behavior of friction stir welding seam were investigated for 6063 aluminum alloy.The corrosion behavior of the base materials and friction stir welding seams were tested in 3.5%（mass fraction）aqueous NaCl solution by static weightloss test,potentiodynamic polarization and electrochemical impedance spectroscopy（EIS）.Meanwhile,their microstructure and corrosion morphology were observed by the optical microscope（OM）and scanning electron microscope（SEM）.The results show that welding joints formed by friction stir welding consists of three regions：a base material zone（BMZ）,a thermo-mechanically affected zone（TANZ）and a weld nugget（WN）.The grains are transformed from coarse block grains in the material zone to fine equiaxed grains in the weld nugget,and a significant plastic flow phenomenon is observed in the thermo-mechanically affected zone,respectively.The results obtained from the static weightloss test suggest that the average corrosion rate of base material and welding seam are 0.078 1、0.231 5、0.347 2 and 0.405 1 g/（m2·h）,respectively.Electrochemical tests show that the corrosion potential of welding seam is more negative than that of basic material,and the corrosion density presents the higher,meanwhile,the oxide resistance and polarization resistance are lower,compared with those of the parent alloy,which indicates that the friction stir welding seam exhibits lower corrosion resistance than the basic material.With increasing in the tool rotation speed,the corrosion resistance of the welding seam is gradually reduced.The pitting and intergranular are main corrosion mechanisms in the corroded areas within the welding seam and basic material of 6063 aluminum alloy.The refinement of grains and increase of grain boundary are responsible for the lower corrosion resistance of the welding seam during friction stir welding.