Increased room temperature formability of Mg AZ31 by high speed Friction Stir Processing

Highlights: • High speed FSP was performed on Mg AZ31 at processing speeds between 1 and 10 m/min. • Process zone EBSD analysis revealed deformation prone microstructure and texture. • The TMAZ featured low aspect ratio grains, with high mounts of HAB. • Formability tests revealed increases of up to 100% over the base material. • Local anisotropy was most present in the tensile regime of the FLD. - Abstract: The aim of this work is to investigate the formability at room temperature of the Mg alloy AZ31 by Friction Stir Processing. Defect-free process zones were created using process speeds of up to 10 m/min, the resulting microstructure and grain size were analyzed. Microstructural zones with varying texture were identified by electron backscatter diffraction. Tensile tests supported by digital image correlation analysis revealed different deformation behavior and enhanced ductility in the thermo mechanically affected zone which was associated with the variation in grain size and texture. Finally, the sheet forming behavior of the processed material was investigated, using the Nakajima test method with Hasek specimen geometries. Forming limit diagrams for several process conditions reveal a continuous increase in formability with increasing processing speed. Additionally, the local anisotropy was analyzed by comparison of the R values at the point of highest strain, to quantify the impact of processing on formability