| In recent years, Cu and Cu alloys have been widely applied in aerospace, electronics, defense industries for their superior mechanical and physical properties. Meanwhile, they are regarded as an important part to study in Yunnan province, where riches in copper ore resources. Optimizing the strength and ductility of Cu and Cu alloys has always been a hotspot in scientific researches and it is also one of the main scientific problems to be resolved. At present, there produces bulk ultra-fine grained (UFG)/nanocrystalline materials by severe plastic deformation (SPD) methods to improve the strength and ductility of material. This paper regards the pure Cu, Cu-Al, Cu-Zn and Cu-Al-Zn alloys with different stacking fault energies (SFEs) as the research object, and mainly discusses the influence of SPD methods on the microstructure and mechanical properties of materials, such as low temperature rolling (LR), room temperature rolling (RR), Split Hopkinson Pressure Bar (SHPB), surface mechanical attrition treatment (SMAT) deformation. And the main deformation mechanism of materials under different deformation methods is also studied. The external parameters during the deformation process, such as strain rate and deformation temperature have impact with different degrees on the microstructure, mechanical properties and deformation mechanism of materials. In order to understand the effect of deformation parameters on mechanical properties and deformation mechanism of Cu alloy, experiments are designed accordingly: Cu-5.5wt%Al-4.5wt% Zn, Cu-1.86wt%Al-23.89wt%Zn and Cu-1.08wt%Al-2.6wt%Zn were rolled both at low temperature and room temperature; Cu, Cu-2.2wt%Al and Cu-4.5wt%Al were conducted both SHPB and room temperature rolling; Cu-10wt%Zn, Cu-20wt%Zn and Cu-30wt%Zn were annealed and processed by cryogenic SMAT, respectively. In the study, the microstructure and mechanical properties of samples processed using different deformation methods were characterized by Viker microhardness tester, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray diffraction (XRD) and Shimadzu Universal Tester. The experimental results show that the deformation temperature has an important effect on microstructure and mechanical properties of materials. The same material deformed via rolling at low temperature (-77K) exhibited higher strength and better ductility than those deformed via rolling at room temperature (-293K). Moreover, the grain size of the LR samples was smaller than that of the RR samples. Cu-5.5wt%Al-4.5wt%Zn alloy processed by low temperature rolling showed the smallest grain (21 nm) and the highest strength (785 MPa). The classic Hall-Petch relationship shows that decreasing grain size within a scale can improve the mechanical properties of materials. The strain rate of Hopkinson process is 104s-1, which is significantly higher than the room temperature rolling technology with the strain rate of 5 s-1. And increasing strain rate contributes to improving the strength and ductility of materials in a certain range. Cu-4.5wt%Al alloy processed by SHPB has improved yield strength (703 MPa) and acceptable uniform elongation (2.1%). Zener-Hollomon parameter (Z value) is inversely proportional to deformation temperature but proportional to the strain rate, thus the samples of liquid nitrogen temperature rolling and Hopkinson process have higher Z value. The increase of Z value will inhibit the dynamic recovery, which helps improve the ability of dislocation pile-up and promote the formation of abundant deformation twins in the process of plastic deformation. Twinning can promote the work hardening, which results in delaying the onset of necking, thus improving the ductility of materials. Consequently, the samples deformed via Hopkinson process exhibit better mechanical properties compared with rolling at room temperature. Alloys processed by SMAT at liquid nitrogen temperature have excellent comprehensive mechanical properties with high strength and good ductility. Tensile tests showed superior strength-ductility synergy for the SMAT samples. Meanwhile, Cu-30wt%Zn shows improved yield strength (364MPa) and acceptable uniform elongation (24%), because the method leads to the formation of a gradient structure with surface fine-grained regions and coarse-grained interior. Moreover, SFE is an intrinsic parameter for materials and Cu alloys with different compositions have different stacking fault energies. Lowering SFE can promote the formation of dislocations and twins, resulting in a finer grain size. This paper also studied that the effect of different SFE and processing conditions on microstructure and mechanical properties of material, and discusses their role in the deformation mechanism. |
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