Grain refinement using equal channel angular extrusion in bulk sections of copper 101 and aluminum alloys 3003 and 6061

Abstract

A new technique called Equal Channel Angular Extrusion (ECAE) which produces intense and uniform deformation by simple shear is applied to 1x1x6" billets of copper 101 and aluminum alloys 3003 and 6061. Two types of refined microstructure are distinguished by optical and transmission electron microscopy: one created through rotation recrystallization with a grain size of 0.2-0.5 gm and the other obtained after extrusion followed by annealing causing static migration recrystallization, with a grain size of 2-10 gm. The properties and grain size of the submicrostructured materials are equivalent to or better than those found in thin sections of materials processed by conventional means to give the maximum properties. Evidence is presented that intense simple shear deformation promotes dynamic rotation recrystallization. In Al 3003 and Cu 101, increasing the number of ECAE passes causes strength to reach saturation and grain refinement to stabilize after four passes. For multipass ECAE with billet orientation constant (route A) or rotated 90' between all passes (route B), a similar structural evolution is observed. Large angle shear bands are created which contain elongated subgrains that become more equiaxed and misoriented as the number of extrusion passes increases. For a billet rotation of 180' between passes (route C), an unusual event is observed. At each even numbered pass, subgrains without shear bands are present inside the old grains which form a more equiaxed and uniform structure than obtained via routes A or B. Route B gives the highest strength whereas route C produces the most stable submicrostructure. In Al 6061, pre-extrusion aging promotes the creation of a strong, uniform, equiaxed and misoriented submicrostructure that is very stable after extrusion and annealing. Lower temperature deformation enhances strength whereas the number of passes has a small influence on peak aged material. For overaged material, these effects are inverted and the structure appears less strong, stable and. uniform. Multistep refinement with annealing between passes facilitates the creation of an equiaxed, uniform and Disoriented structure but does not refine grains more than a simple multipass operation.