Through-thickness diversity of properties in friction stir welded 2219-T87 thick aluminum alloy plate

Friction stir welding of 2219-T87 high-strength aluminum alloy plate in 35 mm thickness was completed with a single pass.The results demonstrate that the tensile strength of weld reaches 274MPa, and the fracture happens in the WNZ (welding nugget zone).Because the welding speed was slow for welding thick plate, and the temperature of the upper WNZ was higher, the microstructure became coarse under the pumping action of screwed stirrer. While the temperature of the bottom WNZ was lower, the microstructure became compact under the crushing action of screwed stirrer. The microhardness of upper WNZ had a decrease zone, while that of bottom changed slowly.When the welding thickness was too large, the microstructure of upper WNZ will become coarse for pumping of screwed stirrer, and it can cause microhardness decrease.It was the reason why the tensile property not high and the fracture was located in the WNZ.