Effects of Y element and dual-step rolling on microstructure and mechanical properties of CuAlMn alloy
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摘要: Cu基形状记忆合金由于晶粒粗大和弹性各向异性，呈现出较低的力学断裂强度和塑性形变能力。本文通过添加微量稀土Y元素制备了系列Cu-11.36Al-5Mn合金，并经热轧和双步轧制(热轧+冷轧)实现了对合金微观结构的调控。实验发现，CuAlMn合金由奥氏体和少量的18R马氏体组成。Y元素添加后，晶粒得到显著细化，基体中可见沿晶分布的含Y沉淀析出相以及伴生的富Al相，热轧形变后晶粒进一步细化，高密度位错和位错胞元结构出现。双步轧制退火后，位错密度持续增大并出现了高密度位错缠结，沿晶析出大量富铜 沉淀相，孪晶和马氏体条交替排列。拉伸力学性能测试表明，稀土Y元素可显著提升合金的力学性能，热轧和双步轧制后进一步提高，拉伸断裂强度从366.67 MPa (原始态)→546.99 MPa (0.4% Y )→879.25 MPa (80%热轧)→
1025.25 MPa (60%热轧-60%冷轧)。断后伸长率与拉伸断裂强度具有相同的变化趋势，从原始态的3.05%提升至双步轧制形变后的8.38%。最大超弹性应变随Y元素的添加而增大，但相同应变下原始态CuAlMn具有更高的超弹性，且经历轧制形变后超弹性应变迅速下降。最后，通过微观结构的演变系统讨论了合金力学性能提升机制。Abstract: Cu-based shape memory alloys exhibit lower mechanical fracture strength and plastic deformation capability due to the coarse grain size and elastic anisotropy. A series of Cu-11.36Al-5Mn alloys were prepared by adding trace amounts of the rare earth element Y, and the microstructure control was achieved through hot rolling and dual-step rolling (hot rolling + cold rolling). It is revealed that the CuAlMn alloy is composed of austenite and a small amount of 18R martensite. A significant refinement of grains was obtained after the addition of Y element. Besides, Y-containing precipitates and Al-rich phases were observed to distribute along the grain boundary within the matrix. After hot rolling deformation, the alloy grains further refined and high-density dislocations and dislocation cell structures appeared. The dislocation density continued to increase accompanied by the emergence of high-density dislocation tangles after dual-step rolling and subsequent annealing. Abundant Cu-rich precipitates precipitated along the grain boundaries, with alternating arrangements of twins and martensite laths. Tensile mechanical property tests show that the mechanical properties are significantly enhanced due to the inclusion of the rare earth element Y, with further improvement after rolling deformation. The tensile fracture strength increases from 366.67 MPa (as-received condition) → 546.99 MPa (0.4% Y addition)→ 879.25 MPa (80% hot rolling) →1025.25 MPa (60% hot rolling + 60% cold rolling). The elongation of the alloy increases from 3.05% in the as-received state to 8.38% after dual-step rolling deformation with the similar trend as tensile fracture strength. The maximum superelastic strain increases with the addition of the Y element, but under the same strain, the as-received CuAlMn alloy exhibits higher superelasticity. Furthermore, the superelastic strain rapidly decreases after undergoing rolling deformation. In end, the microstructural origins of the improved mechanical properties were discussed in detail.-
Key words:
- CuAlMn alloy /
- dual-step rolling /
- microstructure /
- mechanical property /
- rare earth Y addition
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图 2 Cu-11.36Al-5Mn-xY(x=0, 0.4)合金DSC曲线
Figure 2. DSC curves of Cu-11.36Al-5Mn-xY(x=0, 0.4) alloys
图 3 Cu-11.36Al-5Mn-xY(x=0, 0.4)合金XRD谱图
Figure 3. XRD patterns of Cu-11.36 Al-xY(x=0, 0.4) alloys
图 4 Cu-11.36Al-5Mn-0.4Y合金TEM和SEM微观图像：(a) 明场图；(b) (a)中蓝色虚线框的选取电子衍射；(c) 析出相的明场图；(d) (c)的元素分布；(e) (c)中黄色虚线框的选取电子衍射；(f) 析出相的点扫结果
Figure 4. TEM and SEM microstructures of Cu-11.36Al-5Mn-0.4Y alloy: (a) bright-field image; (b) corresponding selected area electron diffraction (SAED) pattern of area in blue dashed box in (a); (c) bright-field image of precipitate phase; (d) elemental distribution of (c); (e) corresponding SAED pattern of area in yellow dashed box in (c); (f) result of EDS point scanning of precipitate phase
图 5 Cu-11.36Al-5Mn-xY合金拉伸力学性能：(a) 应力-应变曲线；(b) 拉伸断裂强度和断后伸长率
Figure 5. Tensile mechanical properties of Cu-11.36Al-5Mn-xY alloys: (a) stress-strain curves; (b) tensile strength and elongation
图 6 热轧Cu-11.36Al-5Mn-0.4Y合金金相显微组织：(a) 未轧制；(b) 20%HR；(c) 40%HR；(d) 60%HR；(e) 80%HR；(f) 平均晶粒尺寸
Figure 6. Metallographic microstructures of hot rolled Cu-11.36Al-5Mn-0.4Y alloys: (a) unrolled; (b) 20%HR; (c) 40%HR; (d) 60%HR; (e) 80%HR; (f) average grain size
图 7 热轧Cu-11.36Al-5Mn-0.4Y合金XRD谱图
Figure 7. XRD patterns of hot rolled Cu-11.36Al-5Mn-0.4Y alloys
图 8 60% HR Cu-11.36Al-5Mn-0.4Y 合金TEM微观图像：(a) 高分辨图像，插图为黄色区域的放大图；(b) (a)图的FFT衍射图；(c) 低倍率明场图；(d) 位错明场图
Figure 8. TEM microstructures of 60% HR Cu-11.36Al-5Mn-0.4Y alloy: (a) high-resolution image, the inset shows the high magnification image of area in yellow dashed box; (b) fast Fourier transform (FFT) pattern of (a); (c) bright-field image; (d) bright-field image of dislocations
图 9 双步轧制Cu-11.36Al-5Mn-0.4Y合金XRD谱图：(a) 60%HR；(b) 80%HR；(1) 20%CR；(2) 40%CR；(3) 60%CR
Figure 9. XRD patterns of two-step rolled Cu-11.36Al-5Mn-0.4Y alloys: (a) 60%HR; (b) 80%HR; (1) 20%CR; (2) 40%CR; (3) 60%CR
图 10 双步轧制Cu-11.36Al-5Mn-0.4金相显微组织：(a) 60%HR；(b) 80%HR； (1) 20%CR；(2) 40%CR；(3) 60%CR
Figure 10. Metallographic microstructure of two-step rolled Cu-11.36Al-5Mn-0.4 alloy: (a) 60%HR; (b) 80%HR; (1) 20%CR; (2) 40%CR; (3) 60%CR
图 11 双步轧制Cu-11.36Al-5Mn-0.4Y合金SEM微观图像和EDS点扫结果：(a) 60%HR-60%CR；(b) 80%HR-60%CR
Figure 11. SEM microstructure and result of EDS point scanning of two-step rolled Cu-11.36Al-5Mn-0.4Y alloy: (a) 60%HR-60%CR; (b) 80%HR-60%CR
图 12 60%HR-60%CR Cu-11.36Al-5Mn-0.4Y合金α相微观组织：(a/c) α相明场图；(b) (a)中黄色虚线区域选取电子衍射
Figure 12. α phase microstructures of 60% HR and 60% CR Cu-11.36Al-5Mn-0.4Y alloy: (a/c) bright-field image of α phase; (b) SAED pattern of area in yellow dashed box in (a)
图 13 60%HR-60%CR Cu-11.36Al-5Mn-0.4Y合金TEM微观图像：(a) 明场图；(b) (a)中蓝色虚线框的分辨图像；(c) (b)的FFT衍射图；(d) (b)的IFFT图；(e/f) 位错的明场图；(g/h) 析出相的STEM图和元素分布，插图为A和B区域的选取电子衍射
Figure 13. TEM microstructures of 60% HR and 60% CR Cu-11.36Al-5Mn-0.4Y alloy: (a) bright-field image; (b) high-resolution image of area in blue dashed box in (a); (c) FFT pattern of (b); (d) inverse fast Fourier transform (IFFT) pattern of (b); (e/f) bright-field image of dislocations; (g/h) STEM image and elemental distribution of precipitate phase, inset shows the SAED pattern of area A and B
图 14 热轧Cu-11.36Al-5Mn-0.4Y合金拉伸力学性能：(a)应力-应变曲线；(b) 拉伸断裂强度和断后伸长率
Figure 14. Tensile mechanical properties of Cu-11.36Al-5Mn-xY alloys: (a) stress-strain curves; (b) tensile strength and elongation
图 15 双步轧制Cu-11.36Al-5Mn-0.4合金拉伸力学性能：(a) 应力-应变曲线；(b) 拉伸断裂强度和断后伸长率
Figure 15. Tensile mechanical properties of two-step rolled Cu-11.36Al-5Mn-0.4Y alloy: (a) stress-strain curves; (b) tensile strength and elongation
图 16 合金拉伸断口形貌：(a) Cu-11.36Al-5Mn;(b) Cu-11.36Al-5Mn-0.4Y (1) unrolled；(2) 60%HR；(3) 60%HR-60%CR
Figure 16. Tensile fracture morphologies (a) Cu-11.36Al-5Mn; (b) Cu-11.36Al-5Mn-0.4Y; (1) unrolled; (2) 60%HR; (3) 60%HR-60%CR
图 17 合金拉伸循环应力-应变曲线：(a) Cu-11.36Al-5Mn; (b) Cu-11.36Al-5Mn-0.4Y; (1) unrolled; (2) 60%HR; (3) 60%HR-60%CR
Figure 17. Cyclic stress-strain curves of alloys: (a) Cu-11.36Al-5Mn; (b) Cu-11.36Al-5Mn-0.4Y; (1) unrolled; (2) 60%HR; (3) 60%HR-60%CR
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