Microstructure and superelasticity control by rolling and heat treatment in columnar-grained Cu-Al-Mn shape memory alloy

Abstract The effects of rolling and heat treatment on the microstructure and superelasticity of columnar-grained Cu 71 Al 18 Mn 11 shape memory alloy were investigated in this paper. Two different rolling strategies were adopted: (i) multipass high-temperature rolling (HR); (ii) one-pass HR followed by several-pass cold rolling (HR+ n CR). For the first rolling strategy, the results showed that columnar-grained microstructure was reserved after one-pass HR at 800 °C with rolling reduction of above 80%, and recrystallization would occur if more HR processes were applied. The superelastic strain could reach 5.9% in multipass HR sample through microstructure control by annealing at 800 °C. For the second rolling strategy, after the first pass HR with the reduction of 80% and annealing at 550 °C, the alloy could be cold rolled at room temperature with total reduction of 50–70%. The columnar-grained microstructure still existed in the cold-rolled alloy which consisted of two phases (i.e. β 1 +α). After recrystallization annealing, the HR+ n CR alloy tend to form texture along the rolling direction, which was helpful to obtain high superelasticity. Finally, the grain growth heat treatment was used to further improve the superelasticity of the cold-rolled alloy. After 2–3 times abnormal grain growth heat treatment, the grains of the alloy could grow up from several hundred micrometers to more than one centimeter in diameter; they still had strong texture along the rolling direction, which enabled the superelastic strain of as high as about 7%.