The Effects of Rolling Process on the Microstructure and Properties of Columnar-Grained Cu-12 Wt%Al Alloys

Abstract

Cu-12 wt.%Al (Cu-12Al) alloy fabricated by continuous unidirectional solidification (CUS) process has high elasticity, high strength, high conductivity, high plasticity and other good comprehensive properties, which has a potential to develop into a high-performance elastic material as the alternative to beryllium bronze. Especially, the room temperature tensile elongation of the columnar-grained structure (CGS) Cu-12Al alloy with high <001>β orientation along the axial direction exceeded 20%, which is six times more than that of the ordinary polycrystalline structure (OPS) Cu-12Al alloy (ε=2-4%) fabricated by traditional casting. The CGS Cu-12Al alloy shows lower flow stress and work-hardening rate during plastic deformation, which determines a dramatic improvement of workability comparing with the OPS alloy. In the present paper, both the effects of the rolling process and its parameters on the microstructure and properties of the CGS Cu-12Al alloy sheets were investigated. The results showed that the CGS sheets (σb=310 MPa, ε=19%) have the maximum reduction of 80% and remain columnar-grained structure after the first rolling pass at 700. After deformation the tensile strength was 401 MPa and the tensile elongation approached to 14%. Then, the hot rolled sheets were rolled again through the second pass at 325 and 700, respectively. The maximum reduction of CGS sheets at 325 warm rolling was 20%, the sheets remain columnar-grained structure and β1'α1' martensitic phase transformation occured; The second pass hot-rolling at 700 showed that the maximum reduction exceeded 60%, and the recrystallization occured in the sheets. After two passes of hot-rolling (total deformation was 92%), although the recrystallization occured, the CGS sheets remained columnar-grained structure (CGS) high tensile elongation (8.3%), which is two times more than that of the as-cast OPS sheets, and is five times as much as the OPS sheets with the same total deformation.