Abstract: 2 mm Al 6013-T4 alloy thin plates were welded by friction stir welding in experiment,and the ratio of rotating speed of the stir pin to the welding speed ω/v,was used to indicate the friction stir welding heat input.The effect of friction stir welding heat input on the weld appearance and mechanical properties of the joint was studied and the microstructure of the joint was analyzed.The results show that the 6013-T4 Al alloy joint by friction stir welding has the better mechanical properties,the yield strength and tensile strength of the joint can reach up to 75.8% and 83.3%,respectively,ant they decrease with the heat input being increased at the different rotating speed of the stir pin.When the ω/v is 3 round/mm or so,the 6013-T4 Al alloy weld appearance will be good with few flashes.The analysis on the microstructure of the joint shows that the microstructure in the base metal is lath,the microstructure in the heat affected zone is similar to and little larger than that in the base metal.The microstructure in thermal-mechanical affected zone is much coarse and uneven in size,which includes the equiaxed grains and some elongated banded microstructure.In weld nugget zone,the microstructure consists of fine equiaxed grains.