Development of a submicrometer-grained microstructure in aluminum 6061 using equal channel angular extrusion

Submicrometer-grained (SMG) microstructures are produced in an Al-Mg-Si alloy (6061) by subjecting peak-aged and overaged billets of the alloy to intense plastic strain by a process known as equal channel angular extrusion. Two types of refined structure are distinguished by optical and transmission electron microscopy. One structure is created through intense deformation (four extrusion passes through a 90 degrees die, epsilon = 4.62) by dynamic rotational recrystallization and is a well-formed grain (fragmented) structure with a mean fragment or grain size of 0.2-0.4 mu m. The other structure is produced by post-extrusion annealing through static migration recrystallization, resulting in a grain size of 5-15 mu m. Intense deformation bf peak-aged material to a true strain epsilon of 4.62 (four passes) produces a strong, ductile, uniform, fine, and high angle grain boundary microstructure with increased stability against static recrystallization as compared to the overaged material.