Formability and microstructural stability of friction stir welded Al alloy tube during subsequent spinning and post weld heat treatment

Subsequent spinning combined with post weld heat treatment (PWHT) was imposed to the friction-stir welding tube, and the effects of PWHT on the formability and microstructural stability of the FSW tubes were investigated in detail. The formability of tubes, evaluated by the hydraulic bulge test, is significantly improved after spinning and PWHT due to the grain refinement, removal of the thickness reduction and heterogeneous microstructure of the weld. Even abnormal grain growth occurs, the tubes still show a relatively high formability compared to the extruded tubes. The PWHT process plays key roles in controlling the size of precipitates and subgrains, and consequently dominates the microstructure stability that is correlated to the strain hardenability and formability of the tubes.