Microstructure and mechanical properties of Al/Cu/Mg laminated composite sheets produced by the ARB proces

In the present study, an Al/Cu/Mg multi-layered composite was produced by accumulative roll bonding(ARB) through seven passes, and its microstructure and mechanical properties were evaluated. The microstructure investigations show that plastic instability occurred in both the copper and magnesium reinforcements in the primary sandwich. In addition, a composite with a perfectly uniform distribution of copper and magnesium reinforcing layers was produced during the last pass. By increasing the number of ARB cycles, the microhardness of the layers including aluminum, copper, and magnesium was significantly increased. The ultimate tensile strength of the sandwich was enhanced continually and reached a maximum value of 355.5 MPa. This strength value was about 3.2, 2, and 2.1 times higher than the initial strength values for the aluminum, copper, and magnesium sheets, respectively. Investigation of tensile fracture surfaces during the ARB process indicated that the fracture mechanism changed to shear ductile at the seventh pass.

新型强塑性变形—静液循环挤压压缩加工AZ91镁合金及其表征

通过静液循环挤压压缩(HCEC)强塑性变形法加工具有较大高径比的密排六方金属棒,并研究其性能。对AZ91镁合金进行两个连续循环加工,研究其显微组织演化、力学性能和腐蚀行为。结果表明,HCEC加工可成功制备超细晶镁合金长棒材,且可同时提高其强度和韧性。经二次循环加工后,样品的抗拉强度和伸长率分别为铸态样品的2.46倍和3.8倍,显微硬度分布更加均匀,其平均值增加了116%。对于加工后的样品,从极化曲线得到的电位较高,电流较低,从Nyquist曲线得到的电容弧直径更大。有限元分析表明,与传统的循环挤压压缩相比,HCEC载荷与长度无关。HCEC是一种特殊的强塑性变形方法,可以制备兼具良好力学性能和耐腐蚀性能的超细晶镁合金长棒材。

Recrystallization and mechanical properties of WE43 magnesium alloy processed via cyclic expansion extrusion

In this study, cyclic expansion extrusion（CEE）, as a relatively new severe plastic deformation（SPD） process, is applied to a rare earth（RE） containing Mg alloy WE43. The effects of the processing temperature and the number of passes are also investigated. The results showed that dynamic recrystallization（DRX） occurred after CEE processing at 400°C, and a bimodal structure with ultrafine DRXed grains surrounded the unrecrystallized grains. However, the DRX at 330°C was retarded because of the existence of RE elements. The tensile tests showed that a simultaneous increase in the strength and the ductility of WE43 is obtained after CEE processing at 400°C via two passes. Furthermore, the highest ultimate tensile strength of 440 MPa was achieved after the second pass of CEE at 330°C, and the highest ductility of 21% was attained after the second pass of CEE at 400°C. The microhardness measurements showed that the hardness increased from HV 80 to HV 114 and HV 98 after two passes of CEE processing at 330 and 400°C, respectively. In conclusion, increasing the processing passes could increase the mechanical properties and the volume fraction of the recrystallized grains. Moreover, increasing the temperature reduced the strength and the microhardness even if the elongation increased.

新型SPD工艺对AM60镁合金性能不均匀性的影响

利用新型大塑性变形(SPD)技术提高镁合金的冶金性能。在此过程中,先进行循环挤压−压缩−角挤压(CECAP)过程,再在出口处进行挤压,起到附加背压的作用。因此,与等径角挤压(ECAP)相比,期望获得更加均匀和优异的力学性能。为了评价这种新方法的有效性和能力,对AM60镁合金进行加工。有限元分析表明,新方法的应变值和均匀应变分布均显著提高。此外,与传统的ECAP相比,新方法的压应力增加约110%。实验结果表明,经新工艺处理后,试样的硬度和强度均有显著提高,这是由于其晶粒细化,显微组织更加均匀,并且细化的β相沿晶界均匀分布。因此,该新工艺在未来镁合金生产中具有广阔的应用前景。

Processing of AM60 magnesium alloy by hydrostatic cyclic expansion extrusion at elevated temperature as a new severe plastic deformation method

Hydrostatic cyclic expansion extrusion(HCEE) process at elevated temperatures is proposed as a method for processing less deformable materials such as magnesium and for producing long ultrafine-grained rods. In the HCEE process at elevated temperatures, high-pressure molten linear low-density polyethylene(LLDPE) was used as a fluid to eliminate frictional forces. To study the capability of the process,AM60 magnesium rods were processed and the properties were investigated. The mechanical properties were found to improve significantly after the HCEE process. The yield and ultimate strengths increased from initial values of 138 and 221 MPa to 212 and 317 MPa, respectively.Moreover, the elongation was enhanced due to the refined grains and the existence of high hydrostatic pressure. Furthermore, the microhardness was increased from HV 55.0 to HV 72.5. The microstructural analysis revealed that ultrafine-grained structure could be produced by the HCEE process. Moreover, the size of the particles decreased, and these particles thoroughly scattered between the grains. Finite element analysis showed that the HCEE was independent of the length of the sample, which makes the process suitable for industrial applications.

等通道转角挤压及后续热处理参数对半固态7075铝合金显微组织的影响（英文）

研究等通道转角挤压(ECAP)及后续加热到半固态温度对7075铝合金显微组织的影响。7075铝合金的显微组织受ECAP道次、ECAP路径、后续加热温度和保温时间等参数的影响。采用实验及Taguchi法探讨上述参数对7075铝合金的微观特性包括晶粒尺寸及形状因子的影响。结果表明:5道次ECAP、路径BA及后续630°C等温处理15 min是合金获得半固态显微组织的较佳工艺条件;加工路径和保温时间对晶粒尺寸的影响最大,而ECAP道次和加热温度对晶粒尺寸的影响最小。形状因子受加工路径、保温时间和加热温度的影响较大,而受ECAP道次的影响较小。

Texture evolution and mechanical anisotropy of an ultrafine/nano-grained pure copper tube processed via hydrostatic tube cyclic expansion extrusion

Texture evolution and mechanical anisotropic behavior of an ultrafine-grained(UFG)pure copper tube processed by recently introduced method of hydrostatic tube cyclic expansion extrusion(HTCEE)was investigated.For the UFG tube,different deformation behavior and a significant anisotropy in tensile properties were recorded along the longitudinal and peripheral directions.The HTCEE process increased the yield strength and the ultimate strength in the axial direction by 3.6 and 1.67 times,respectively.Also,this process increased the yield strength and the ultimate strength in the peripheral direction by 1.15 and 1.12 times,respectively.The ratio of ultimate tensile strength in the peripheral direction to that in the axial direction,as a criterion for mechanical anisotropy,are 1.7 and 1.16 for the as-annealed coarse-grained and the HTCEE processed UFG tube,respectively.The results are indicative of a reducing effect of the HTCEE process on the mechanical anisotropy.Besides,after HTCEE process,a low loss of ductility was observed in both directions,which is another advantage of HTCEE process.Hardness measurements revealed a slight increment of hardness values in the peripheral direction,which is in agreement with the trend of tensile tests.Texture analysis was conducted in order to determine the oriental distribution of the grains.The obtained{111}pole figures demonstrate the texture evolution and reaffirm the anisotropy observed in mechanical properties.Scanning electron microscopy micrographs showed that different modes of fracture occurred after tensile testing in the two orthogonal directions.

Simulation of Fatigue Life Behavior of Circular Cross-Section Bar with Straight-Fronted Crack

In this paper, fatigue life circular cross-section elastic bar under pure fatigue axial loading is studied through principles of linear elastic fracture mechanics (LEFM) coupled with the three-dimensional finite element technique for determination of critical crack size and residual lifetime. Three different initial notch depths are discussed. The relations between aspect ratio (b/c) and relative crack depth (b/D) are obtained, and it is shown that there is great difference in the growth of cracks with different front shapes and initial notch depths.