Correlation between microstructure, tensile properties and fatigue life of AA1050 aluminum alloy processed by pure shear extrusion

This research is focused on the influence of multiple passes of pure shear extrusion (PSE) on grain refinement and evolution of tensile properties in AA1050 alloy. It is observed that the average cell size reduces and the misorientation angle increases with increasing number of PSE passes. High fractions of elongated grains are observed in the microstructures of the samples deformed by 1, 2 and 3 PSE passes. However, the fraction of elongated grains reduces by increasing number of PSE passes and diminishes at the 4-pass of PSE. In fact, by increasing the number of PSE passes, more homogeneous grain refinement occurs which is evidenced by formation of equiaxed cell structures with remarkable percentage of high angle grain boundaries. The most significant increase in yield and tensile strength occurs at the first pass of PSE. Strengthening continues with further PSE processing while elongation gradually improves which is attributed to reducing cell size and increasing the fraction of high angle grain boundaries. Despite of increasing elongation and strength, the fatigue life of the samples continuously reduces with further PSE processing. This is attributed to occurrence of cyclic softening in deformed samples with ultra-high strength.