Neutron Diffraction Residual Stress Mapping of AA2219-T87 Self-reacting Friction Stir Weld

Aluminum alloys of the 2xxx series possess high strength and ductility, low density, good corrosion resistance, and stable performance at cryogenic temperatures in addition to their ability to age harden. Their lightweight and structural stability to temperatures in the liquid hydrogen range make the 2xxx series particularly attractive for structural aerospace components. For many applications and structures, sections of aluminum are joined utilizing friction stir welding. However, this process creates residual stresses which can negatively impact material performance and hasten failure. Therefore, quantifying and developing an understanding of thermal residual stresses is a key area of interest.

This work focuses on the characterization of a self-reacting friction stir weld of AA2219-T87. Neutron diffraction was employed to measure and map the residual stresses in the longitudinal, transverse, and normal directions at 1 mm intervals throughout the stir and heat-affected zones with a coarser measurement scheme to ±70 mm in the transverse direction and ±6.4 mm (normal direction) from the weld plate center. Preliminary data analysis suggests tensile residual stresses are greatest in the longitudinal direction. The residual stresses show characteristic features in each direction with the longitudinal direction displaying an ‘M shaped’ residual stress curve and the transverse and normal direction residual stress curves showing their largest compressive residual stress near the weld center. Features of the welding process such as advancing/retreating side are observable as well.