Neutron Diffraction Investigation of Friction-Stir Processed Aluminum and Magnesium Alloys

Wanchuck (Chuck) Woo, University of Tennessee and Oak Ridge National Lab

Friction-stir welding (FSW) is a solid-state joining process that utilizes a cylindrical rotating tool consisting of a concentric threaded tool pin and tool shoulder. Recently, a number of variations of FSW have been applied to modify the microstructure, namely friction-stir processing (FSP). In this talk, I will present the results of recent neutron-diffraction investigations on the effects of frictional heating and/or severe plastic deformation caused by the tool shoulder and pin on the residual stresses and texture variations in the aluminum and magnesium alloys. The deep-penetration capability of neutrons into most metallic materials makes neutron diffraction a unique and powerful tool for the study of structures and properties of bulk materials. Specifically, three examples will be presented; (i) investigation of the residual strains, texture, and microstructure of the FSP Al 6061-T6 alloy using the neutron diffraction, (ii) the relationship between the texture distributions and the tensile behavior of the FSP AZ-31B Mg alloy, and (iii) in-situ neutron-diffraction measurements of transient temperature and stress fields using the quasi-steady-state principle to decompose the thermal and elastic strains from the measured lattice spacing changes. At the end, future research plans will be presented, e.g., the in-situ investigation of microstructures and/or deformation micromechanics of bulk ultrafine/nano-structured metallic alloys and composites using neutron diffraction.

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