On the role of applying groove pressing technique before friction stir processing of copper: microstructure and mechanical evaluation

The effect of prior constrained groove pressing on friction stir processing (FSP) of pure copper was investigated. The results illustrate the development of high strain and strength of FSP samples along with an increased strength base metal as a result of applying for a prior constrained groove pressing (CGP) pass. The influences of further FSP passes on the microstructures, and mechanical properties were also shown. The microstructural evaluation of the specimens indicated up to 10 times grain size reduction in FSP specimens as well as equiaxed microstructural morphology. Mechanical properties of the specimens were carried out through tensile and microhardness tests. It was demonstrated that the FSP could improve the strength and ductility of the specimens simultaneously through improved mechanical properties of the base metal resulting from prior CGP. The performed calculations show that values of dislocation density of the CGPed specimens experienced significant change after applying for FSP passes