On the contribution of boundaries towards strength in oxygen free high conductivity copper subjected to repetitive upsetting - extrusion

Oxygen free high conductivity (OFHC) copper was subjected to 1, 5, 10, 15 and 20 cycles of repetitive upsetting and extrusion (RUE) process at room temperature. Microstructure and microhardness in the RUE processed material were evaluated at specific locations and correlated with the equivalent plastic strain. The microhardness of the material was found to be independent of strain or number of RUE cycles at certain locations whereas it exhibited strain softening behaviour at certain locations even though significant grain refinement was achieved. This difference in behaviour is attributed to the varied strength contribution from different types of boundaries present in the material after deformation.