An effective method to obtain Cu-35Zn alloy with a good combination of strength and ductility through cryogenic rolling

In the present study, commercial Cu-35Zn alpha-brass sheets were subjected to cryogenic rolling (CR) to obtain samples with different amounts of deformation in the thickness direction. A self-designed liquid nitrogen cooling system that can simultaneously cool the work rollers and samples was used to ensure an ultra-low temperature condition during the rolling process. The grains, deformation twins, and dislocation density of the samples were studied by optical microscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). Uniaxial tensile tests and Vickers hardness measurements were conducted to measure the mechanical properties of the samples. The microstructures and mechanical properties of CR samples were apparently improved compared to the room temperature rolling (RTR) samples with increasing deformation amount. As a typical example, when the deformation amount is 90%, the CR sample possesses ultrafine microstructures and demonstrates extraordinary mechanical properties. The average tensile and yield strengths of a 90% deformation CR sample can be improved to 835.3 MPa and 711.5 MPa, while those of a 90% deformation RTR sample are 718.6 MPa and 481.2 MPa. The average elongation of the CR sample is 2.9%, which is acceptable compared with the RTR sample whose average elongation is 3.1%. The ultrafine microstructures containing ultrafine grains, high density dislocation, and nanometer scale deformation twins in the 90% deformation CR sample may be the main reason for its extraordinary mechanical properties. Therefore, samples with a good combination of strength and ductility were obtained in the present study. This may be a valuable exploration to fabricate Cu-35Zn alloy sheets with excellent microstructures and mechanical properties.