PNNL

Abstract

Friction Extrusion (FE) is an emerging solid phase processing technique that has demonstrated significant improvement in the physical properties and performance of metallic materials. The combination of large shear stresses and temperatures produced at the interface between the tool and the billet during the FE process develops a homogenized microstructure, refines the grains and uniformly distributes the precipitates in the matrix. In the present study, fully consolidated, defect-free 5 mm diameter rods of 7075 alloy were extruded using the FE process resulting in dynamically recrystallized equiaxed grains with a grain size of 2.0 µm and fine uniformly distributed stable ? (MgZn2) precipitates ~25-100 nm in size. Formation of such a microstructure resulted in lower solutionizing temperature and times (flash annealing) as compared to the conventionally extruded counterparts. Systematic characterization was performed using scanning electron microscope and transmission electron microscope in the longitudinal as well as the transverse cross -sections along the entire length of the rod. The tensile data for samples that were flash annealed and artificially aged after FE processing showed exceptional increases in strength, of UTS by over 19% and YS by over 59%, compared with an as-FE-processed sample.