等通道转角变形与固溶处理对铸态7085铝合金微观组织的影响

在室温下对铸态7085铝合金实施了道次等效应变约为0.5的等通道转角变形(Equal-channel angular pressing-ECAP),对其夹杂物的分布、碎化和合金的硬度进行了考察;并对铝合金进行了470℃/2h+480℃/2h+490℃/2h+淬火三级固溶加T6时效处理。结果表明,ECAP加工将几乎呈连续分布的AlFeCu夹杂物折断碎化并分散开,明显提高了合金的致密性、抗蚀性,并引入了大量位错于铝合金中,提高硬度的幅度达到55.9%;固溶加时效处理后铝合金组织更加致密均匀夹杂物也明显的减少。由的试验结果说明了ECAP+强化固溶+低温人工时效是提升常规7085铝合金的强度、制取超高强铝合金的一条十分有效的途径。

等通道转角变形对铸态3003铝合金夹杂物的影响

本文在室温下对铸态3003铝合金实施了道次等效应变约为0.5的等通道转角变形(Equal-channel angular pressing-ECAP),对其夹杂物的碎化、分布和合金的硬度进行了考察。结果表明,第1道次的ECAP加工将合金内部的粗大(长5-15μm、宽1-2μm)且几乎呈连续分布的夹杂物(AlFe(Mn)Si)折断碎化(长1-3μm)并初步分散开,引入大量位错至合金中,提高硬度幅度达66.7%。后续的2-4道ECAP加工将夹杂物分散均匀,但对夹杂物的碎化和硬度影响很小。本文的试验结果说明了ECAP作为一种细化铝合金内部AlFe(Mn)Si夹杂物并使之分布均匀的工艺方法的可行性。

差热-等通道转角挤压工艺对TZK镁合金微观组织与腐蚀性能的影响

采用光学显微镜、扫描电镜、电化学、X光电子能谱分析等测试技术探究了差热-等通道转角挤压工艺(DT-ECAP)对Mg-5Sn-2Zn-0.5Zr(TZK)镁合金微观组织和腐蚀性能的影响。结果表明,当模具温度为300℃、试样保持室温时(DT-1),TZK镁合金晶粒和第二相显著细化,且第二相呈弥散分布。此外,在DT-1变形条件下,TZK镁合金在Hank′s溶液中呈现均匀腐蚀,腐蚀速率为1.161 mm·a^(-1),腐蚀电位与腐蚀电流密度分别为-1.38 V和5.916×10^(-6)mA·cm^(-2),合金耐蚀性能最优。而当模具温度为300℃、试样温度为200℃(DT-2)以及模具保持室温、试样温度为300℃(DT-3)时,合金中的第二相沿变形方向呈带状分布,且局部区域存在粗大的块状第二相,其在Hank′s溶液中的腐蚀以局部腐蚀为主。

强化固溶态2024铝合金ECAP加工后的拉伸性能

在室温下对经强化固溶处理的2024铝合金实施了等效应变为0.5的等通道转角挤压(ECAP),将强化固溶、形变、时效和晶界细化四者有机结合,制备出超高强铝合金,其硬度、屈服强度、伸长率分别高达约191 HV,610 MPa和13%.强度结构关系的定量计算表明,ECAP变形过程中所引入的位错,其对强度提升的贡献高达整个强度提高值的62.2%.研究结果还表明,强化固溶→低温ECAP变形→低温人工时效是提升常规铝合金的强度、制取超高强铝合金的一条有效途径.

超细亚晶粒铝合金的强化机理

在室温下对经过时效处理的2024铝合金实施了等效应变为0.5的等通道转角挤压(ECAP)变形,将形变强化、时效强化和晶界细化强化有机结合,制备出超细亚晶粒铝合金,其硬度、屈服强度、伸长率分别约达100 HV,130 MPa和31%.分析探讨了超细亚晶粒2024铝合金的强化机理.研究结果表明,屈服强度的实测数值和理论计算所得十分吻合,由此证明,过时效态2024铝合金经ECAP加工后,其屈服强度主要取决于基体的屈服强度,并且主要由位错强化、亚晶界强化、晶界强化和晶格摩擦应力等4部分组成.

Equal channel angular extrusion of NiTi shape memory alloy tube

As a new attempt, equal channel angular extrusion （ECAE） of nickel-titanium shape memory alloy （NiTi SMA） tube was investigated by means of process experiment, finite element method （FEM） and microscopy. NiTi SMA tube with the steel core in it was inserted into the steel can during ECAE of NiTi SMA tube. Based on rigid-viscoplastic FEM, multiple coupled boundary conditions and multiple constitutive models were used for finite element simulation of ECAE of NiTi SMA tube, where the effective stress field, the effective strain field and the velocity field were obtained. Finite element simulation results are in good accordance with the experimental ones. Finite element simulation results reveal that the velocity field shows the minimum value in the corner of NiTi SMA tube, where severe shear deformation occurs. Microstructural observation results reveal that severe plastic deformation leads to a certain grain orientation as well as occurrence of substructures in the grain interior and dynamic recovery occurs during ECAE of NiTi SMA tube. ECAE of NiTi SMA tube provides a new approach to manufacturing ultrafine-grained NiTi SMA tube.

Aging behavior and mechanical properties of 6013 aluminum alloy processed by severe plastic deformation

Structural features, aging behavior, precipitation kinetics and mechanical properties of a 6013 Al–Mg–Si aluminum alloy subjected to equal channel angular pressing （ECAP） at different temperatures were comparatively investigated with that in conventional static aging by quantitative X-ray diffraction （XRD） measurements, differential scanning calorimetry （DSC） and tensile tests. Average grain sizes measured by XRD are in the range of 66-112 nm while the average dislocation density is in the range of 1.20×10^14-1.70×10^14 m^-2 in the deformed alloy. The DSC analysis reveals that the precipitation kinetics in the deformed alloy is much faster as compared with the peak-aged sample due to the smaller grains and higher dislocation density developed after ECAP. Both the yield strength （YS） and ultimate tensile strength （UTS） are dramatically increased in all the ECAP samples as compared with the undeformed counterparts. The maximum strength appears in the samples ECAP treated at room temperature and the maximum YS is about 1.6 times that of the statically peak-aged sample. The very high strength in the ECAP alloy is suggested to be related to the grain size strengthening and dislocation strengthening, as well as the precipitation strengthening contributing from the dynamic precipitation during ECAP.

Effect of processing route on grain refinement in pure copper processed by equal channel angular extrusion

An experimental study of the microstructures in pure copper billets processed by 8 passes of equal channel angular extrusion （ECAE） via an extended range of processing routes with a 90° die is carried out. Each processing route is defined according to the inter-pass billet rotation angle （χ）, which varies from 0° to 180°. According to the generation of high-angle boundaries and reduction of grain size by electron backscatter diffraction （EBSD） measurements, the grain refinement is found to be most efficient for route with χ=90°and least efficient with χ=180°, among the seven routes studied. This trend is supported by supplementary transmission electron microscopy （TEM） measurements. Comparison of the EBSD and TEM data reveals the importance of considering the non-equiaxity of grain structures in quantitative assessment of microstructural differences in ECAE-processed materials.

Application of crystal plasticity modeling in equal channel angular extrusion

Some applications of crystal plasticity modeling in equal channel angular extrusion（ECAE） of face-centered cubic metals were highlighted.The results show that such simulations can elucidate the dependency of grain refinement efficiency on processing route and the directionality of substructure development,which cannot be explained by theories that consider only the macroscopic deformation behavior.They can also capture satisfactorily the orientation stability and texture evolution under various processing conditions.It is demonstrated that crystal plasticity models are useful tools in exploring the crystallographic nature of grain deformation and associated behavior that are overlooked or sometimes erroneously interpreted by existing phenomenological theories.

Severe plastic deformation of commercially pure aluminum using novel equal channel angular expansion extrusion with spherical cavity

Equal channel angular expansion extrusion with spherical cavity(ECAEE-SC)was introduced as a novel severe plastic deformation(SPD)technique,which is capable of imposing large plastic strain and intrinsic back-pressure on the processed billet.The plastic deformation behaviors of commercially pure aluminum during ECAEE-SC process were investigated using finite element analysis DEFORM-3D simulation software.The material flow,the load history,the distribution of effective strain and mean stress in the billet were analyzed in comparison with conventional equal channel angular extrusion(ECAE)process.In addition,single-pass ECAEE-SC was experimentally conducted on commercially pure aluminum at room temperature for validation,and the evolution of microstructure and microhardness of as-processed material was discussed.It was shown that during the process,the material is in the ideal hydrostatic stress state and the load requirement for ECAEE-SC is much more than that for ECAE.After a single-pass ECAEE-SC,an average strain of 3.51 was accumulated in the billet with homogeneous distribution.Moreover,the microstructure was significantly refined and composed of equiaxed ultrafine grains with sub-micron size.Considerable improvement in the average microhardness of aluminum was also found,which was homogenized and increased from HV 36.61 to HV 70.20,denoting 91.75%improvement compared with that of the as-cast billet.

A new method of characterizing equivalent strain for equal channel angular processing

In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new approach to characterize the equivalent strain was proposed. The results show that there exists better accordance between mechanical property （such as hardness or strength） and equivalent strain after rolling and ECAP in a certain range of deformation amount, and Gauss equation can be satisfied among the equivalent strain and the mechanical properties for ECAP. Through regression analysis on the data of hardness and strength after the deformation, a more generalized expression of equivalent strain for ECAP is proposed as：ε=k0exp[-（k1M-k2）^2], where M is the strength or hardness of the material, k1 is the modified coefficient （k1∈ （0, 1））, ko and k2 are two parameters dependent on the critical strain and mechanical property that reaches saturation state for the material, respectively. In this expression the equivalent strain for ECAP is characterized novelly through the mechanical parameter relating to material property rather than the classical geometry equation.

退火温度对ECAP变形高氮奥氏体不锈钢力学性能的影响

为研究等通道转角挤压(ECAP)+退火对高氮钢力学行为的影响,室温条件下对高氮钢进行1道次ECAP变形,之后分别在700、800、850、900℃下对不同N含量的试验钢进行退火处理,分析其力学性能变化规律。结果表明:高氮钢随着退火温度的升高,屈服强度和抗拉强度整体上呈下降的趋势,塑性随退火温度的升高而上升;不同状态高氮钢的抗拉强度与均匀延伸率之间都呈现了传统的强塑性之间的矛盾关系,随N含量的增加,呈现强度和均匀延伸率同步提高的趋势;高氮钢ECAP+低温退火后的拉伸断口呈现沿晶断裂形貌,随N含量的升高,沿晶断裂倾向更加明显。