Microstructure and Mechanical Properties of Cu-Zn-Si Alloy Bars Produced by Groove Rolling

The hot-extruded bars of a Cu-Zn-Si alloy were subjected to groove rolling. Groove rolling was performed using rolls with grooves of different sizes so that the cross-sectional area of the bars after rolling decreased. The specimen bars were rotated by 90 degrees along the rolling direction after each rolling pass, and rolling was continued up to 68% reduction in cross-sectional area. With increasing rolling reduction, the initial coarse-equiaxed grains macroscopically elongated parallel to the rolling direction. Within the grains, ultrafine mechanical twins were high-densely introduced, which promptly and drastically fragmented the initial coarse grains to develop heterogeneous nanostructure consisting of micro- and nano-meter-ordered mechanical twins. The tensile strength of the as-hot-extruded bar of 464 MPa increased to 704 MPa after 42% reduction, and further increased up to 940 MPa after 68% reduction. The remarkable increase in strength is attributed to the evolution of the heterogeneous nanostructure developed by grain subdivision owing to dense mechanical twinning. It can be concluded, therefore, that the strength of the Cu-Zn-Si alloy bars was significantly increased by the evolution of the heterogeneous nanostructure even by relatively small area reduction of 68%, i.e., equivalent strain of 1.13.