Improving plasticity by Si-addition-induced coherent nanoprecipitates in Cu–Al–Mn alloy fabricated by laser powder bed fusion

In this paper, the Cu-10.8Al-8.3Mn-0.37Si alloy containing Mn₅Si₃ phase was obtained by adding Si element to the Cu-10.8Al-8.3Mn alloy. The two alloys were printed by laser powder bed fusion. The changes in the organization and tensile properties of the alloys and the mechanism were investigated. After Si addition, the Mn₅Si₃ nano phase precipitated in the alloy in addition to the β₁ austenite phase. The Mn₅Si₃ phase was co-lattice with the β₁ phase with an average size of 10 nm and was diffusely distributed. Standard tensile experiments showed that the yield strength of the Cu-10.8Al-8.3Mn-0.37Si alloy decreased by 57.7% and the elongation increased by 266% compared to the Cu-10.8Al-8.3Mn alloy, while the tensile strength remained essentially unchanged. The presence of Mn₅Si₃ phase provided nucleation points for martensite and promoted the generation of stress-induced martensite. Hence the yield strength was reduced. TEM results showed that the β₁ phase in the Cu-10.8Al-8.3Mn-0.37Si alloy was fully transformed into stress-induced martensite after deformation, which displayed the transformation induced plasticity effect and hindered the slip of dislocations. Meanwhile, the Mn₅Si₃ phase was sheared by the stacking faults, which promoted the accumulation of hetero-deformation-induced stress. Therefore, the hardening capacity and plasticity of the Cu-10.8Al-8.3Mn-0.37Si alloy were enhanced. This work provides a new idea for the plasticity enhancement of Cu–Al–Mn-based shape memory alloys achieved by co-lattice nano-precipitated phase strengthening.