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.