Microstructure and Mechanical Properties of Cu-Zn System Alloy Bars Produced by Different Groove Rolling Processes

Groove rolling was applied to Cu-26 mass%Zn-2 mass%Si alloy rods to develop heterogeneous nanostructured (HN-structured) bar products. The effects of different groove rolling processes, i.e., combination of 90° and/or 45°rotations of the rods along rolling direction between rolling passes, on the microstructural evolution and mechanical properties were systematically investigated. The rods were rolled to area reductions of 42% and 68%. The groove-rolled rods were comprising elongated grains with high densities of deformation twins, leading to the formation of ultrafine hierarchical HN-structure by multiple twinning. With increasing area reduction, the area fraction of twinned grains increased, and twin boundary spacing decreased. When compared the tensile strength of the rods rolled to 68%, it decreased in the order of 45° rotations > 90° + 45° combination > 90° rotation, where 90° rotation is the conventional rolling method. The highest strength of the rods fabricated by 45° rotation process was attributed to the highest density of deformation twins due to favorable crystallographical orientations provided for twin formation by 45° rotations. These findings demonstrate that optimization of groove rolling path of rods by incorporating 45° rotations can effectively promote the formation of HN-structure and, therefore, improve the mechanical performance.