Friction stir welding for T-joint of 2A70-T6 aluminum alloy is carried out by using four different kind
of welding tools, the weld cross section is observed and the tensile strength of weld is tested. The results show that the
transition metal at the advancing side deform excessively compared to the retreating side. The joints often break at the
advancing side, under the same welding parameter. The nugget width and the tensile strength increase along with the
diameter of the pin increases in the single-passs weld, but the increment is small. The tensile strength of parallel weld
is about 93% of the single-pass weld. In order to get the same width nugget, it is advantage to adopt single-pass welding
by using big diameter pin over parallel welding.