Mechanical behaviour and microstructural evolution of constrained groove pressed nickel sheets

Pure nickel sheets are subjected to severe plastic deformation by constrained groove pressing technique at room temperature thereby imparting an effective plastic strain of 3.48. The evolution of mechanical behaviour with increasing number of passes revealed intensive increase in strength properties after first pass; however marginal increase is observed subsequently. Gain in ductility which is attributed to dislocation recovery is observed after third pass along with marginal drop in strength. Microstructural evolution during groove pressing of sheets is characterized by X-ray diffraction profile analysis using Williamson–Hall method. Besides the observation of strong shear texture in constrained groove pressed sheets, improvement in strain isotropy with increased straining is revealed from Williamson–Hall plots. The sub-grain/cell size estimated by analysing the diffraction profile of deformed sheets is found to be ～1390 nm after processing up to three passes. Low grain refinement efficiency observed in this process compared to other severe plastic deformation techniques at similar strain conditions is explained by the deformation characteristics and loading behaviour experienced by the sheets during constrained groove pressing.     

AZ31镁合金轧制板材退火后的组织与力学性能

采用单向轧制和交叉轧制工艺分别进行了AZ31镁合金板材轧制实验,分析了轧制板材经退火处理后的组织与力学性能。结果表明:采用单向轧制工艺,当板材最终变形量相等时,经退火处理后的板材大压下量比小压下量得到的微观组织更为细小;交叉轧制得到轧制板材可以缓解镁合金轧制板材在室温下的各向异性,其微观组织较单向轧制均匀,具有更好的冲压成形性能;交叉轧制和单向轧制两种工艺得到的板材微观组织细化效果相似。     

Ta晶粒细化工艺及组织、织构的研究

研究了加工方法对Ta组织及织构的影响,采用径向模压(自行设计的模具)+轴向镦粗的方法,经过2个循环的变形.在真空下1100℃退火1 h,取样观察了钽的微观组织、晶粒度;研究了轧制方式对钽组织均匀性的影响,采用一次交叉轧制的方法,道次加工率为5%～10%,总变形量为70%,真空退火1200℃.经EBSD测定了不同状态下钽的织构.结果表明:模压和轧制方法对钽的力学性能和晶粒大小有重要影响,一次交叉轧制可以更有效地减小钽的各向异性并获得细晶粒,平均晶粒度为30 μm.采用模压更有利于退火态钽板中{111}织构的增强,并减少{100}.     

Post Deformation at Room and Cryogenic Temperature Cooling Media on Severely Deformed 1050-Aluminum

The annealed 1050-aluminum sheets were initially subjected to the severe plastic deformation through two passes of constrained groove pressing (CGP) process. The obtained specimens were post-deformed by friction stir processing at room and cryogenic temperature cooling media. The microstructure evolutions during mentioned processes in terms of grain structure, misorientation distribution, and grain orientation spread (GOS) were characterized using electron backscattered diffraction. The annealed sample contained a large number of “recrystallized” grains and relatively large fraction (78%) of high-angle grain boundaries (HAGBs). When CGP process was applied on the annealed specimen, the elongated grains with interior substructure were developed, which was responsible for the formation of 80% low-angle grain boundaries. The GOS map of the severely deformed specimen manifested the formation of 43% “distorted” and 51% “substructured” grains. The post deformation of severely deformed aluminum at room temperature led to the increase in the fraction of HAGBs from 20 to 60%. Also, it gave rise to the formation of “recrystallized” grains with the average size of 13 μm, which were coarser than the grains predicted by Zener–Hollomon parameter. This was attributed to the occurrence of appreciable grain growth during post deformation. In the case of post deformation at cryogenic temperature cooling medium, the grain size was decreased, which was in well agreement with the predicted grain size. The cumulative distribution of misorientation was the same for both processing routes. Mechanical properties characterizations in terms of nano-indentation and tensile tests revealed that the post deformation process led to the reduction in hardness, yield stress, and ultimate tensile strength of the severely deformed aluminum.     

应变路线对Ti-6242合金组织与力学性能的影响

对两道次轧制的Ti-6242锻坯板材样品进行双级退火处理,研究了3种轧制应变路线对合金板材力学性能的影响。结果表明,不同应变路线的Ti-6242合金具有相近的晶粒尺寸和维氏硬度,采用单向轧制板材样品的力学性能高于两步交叉轧制和交叉换向轧制样品,抗拉强度和断后伸长率分别可以达到1264 MPa和21%;换向轧制会弱化Ti-6242合金板材的晶粒择优取向,而单向轧制则会强化其()显微织构强度。      

Effect of grain shape on the texture evolution during cold rolling of Al-Mg alloys

The hot bands of continuous cast AA 5754 and high-Fe AA 5754 aluminum alloys exhibited elongated grains in the rolling direction after recrystallization annealing. The annealed hot bands were cold rolled to different reductions along the original rolling direction and transverse direction, respectively. The effect of grain shape on texture evolution was investigated by X-ray diffraction. It was found that straight-rolling resulted in a higher rate of disappearance of the r-cube + cube component and a slightly higher rate of formation of the β fiber component than cross-rolling. The elongated grains in the rolling direction were easier to rotate from initial orientations to the β fiber in straight-rolling than in cross-rolling.     

Texture and mechanical properties of Al-0.5Mg-1.0Si-0.5Cu alloy sheets manufactured via a cross rolling method

The relationship between the texture and mechanical properties of 6xxx aluminum alloy sheets processed via cross rolling was investigated. The microstructures of the conventional rolled and cross rolled sheets after annealing were analyzed using optical micrographs (OM). The texture distribution across the thickness in the Al-Mg-Si-Cu alloy, conventional rolled sheets, and cross rolled sheets both before and after annealing was investigated via X-ray texture measurements. The texture was analyzed in three layers from the surface to the center of the sheet. The β-fiber texture of the conventional rolled sheet was typical of the texture obtained using aluminumoll ring. After annealing, the typical β-fiber orientations were changed to recrystallization textures: cube{001}〈100〉 and normal direction (ND)-rotated cubes. However, the texture of the cross rolled sheet was composed of an asymmetrical, rolling direction (RD)-rotated cubes. After annealing, the asymmetrical orientations in the cross rolled sheet were changed to a randomized texture. The average R-value of the annealed cross rolled sheets was higher than that of the conventional rolled sheets. The limit dome height (LDH) test results demonstrated that cross rolling is effective in improving the formability of the Al-Mg-Si-Cu alloy sheets.     

The Role of Oriented Growth in P Texture Development in Al-Mn-Mg Aluminum Alloy

The deformation and recrystallization textures in straight-rolled and cross-rolled AA 3105 aluminum alloy were investigated by x-ray diffraction to determine the role of oriented growth in the formation of the P recrystallization texture. A very strong P texture was developed in the straight-rolled sheet after recrystallization annealing. In contrast, the cross-rolled sheet did not develop the P texture on annealing even though the cross-rolling (i.e., rolling along the original transverse direction) texture contained more orientations close to the P orientation than the straight-rolling texture. The formation of the P texture in aluminum alloys requires the presence of the C component, since the P orientation has a 31.1°〈122〉 orientation relationship with respect to the C orientation. The recrystallization texture in the cross-rolled sheets was in excellent agreement with the oriented growth theory.     

终轧加工率对钼及钼镧合金板材组织及性能的影响

以粉末冶金方法生产的25min×280min×320mm纯钼及钼镧合金板坯为实验原料,研究了不同的热轧终轧加工率对钼及钼镧合金板显微组织及力学性能的影响。结果表明,将纯钼及钼镧合金板热轧终轧加工率控制在50％以上,轧后纯钼板材的显微组织为细化的纤维流线组织,纵、横向的吃分别为795,885MPa,也分别达到27％,21％,其后续的温轧加工不开裂;而钼镧合金板材不论是显微组织,还是力学性能均好于纯钼。进一步的生产实践证明,将钼及钼镧合金板的热轧终轧加工率控制在50％以上,其强度、塑性和硬度匹配良好,弯曲性能和后序的温轧加工性能明显提高。     

Fabrication of ultrafine-grained AA1060 sheets via accumulative roll bonding with subsequent cryorolling

Ultrafine-grained (UFG) AA1060 sheets were fabricated via five-cycle accumulative roll bonding (ARB) and subsequent three-pass cold rolling (298 K), or cryorolling (83 K and 173 K). Microstructures of the aluminum samples were examined via transmission electron microscopy, and their mechanical properties were measured via tensile and microhardness testing. Results indicate that ultrafine grains in ARB-processed sheets were further refined by subsequent rolling, and the grain size became finer with reducing rolling temperature. The mean grain size of 666 nm in the sheets subjected to ARB was refined to 346 or 266 nm, respectively, via subsequent cold rolling or cryorolling (83 K). Subsequent cryorolling resulted in ultrafine-grained sheets of higher strength and ductility than those of the sheets subjected to cold rolling.     

脉冲电流轧制对AZ31镁合金微观组织与力学性能的影响

对比研究脉冲电流轧制工艺与温轧工艺对AZ31镁合金板材的力学性能、织构、微观组织与沉淀相等方面的影响。结果表明：脉冲电流具有促进冷轧AZ31镁合金低温再结晶能力的作用。脉冲电流轧制后的镁合金板材组织由细小的等轴再结晶粒与析出相构成,没有发现孪晶组织,并且完全再结晶,原始晶粒均被细小的再结晶晶粒取代,再结晶晶粒内的位错密度低。而温轧镁合金组织则由稍拉长变形孪晶、粗大的再结晶晶粒和析出相构成,再结晶的晶粒内位错密度高。两种轧制方式下的镁合金析出相均为Mg17Al12。脉冲电流轧制后镁合金的织构具有典型基面织构的特征,而脉冲电流轧制镁合金的织构则出现横向偏转;脉冲电流轧制后镁合金的屈服强度与伸长率均比温轧镁合金的大,但抗拉强度正好相反。     

模压形变对纯铜组织和性能的影响

采用交叉模压形变法对纯铜进行不同道次的形变处理,研究交叉模压形变对纯铜显微组织和力学性能的影响。研究结果表明:交叉模压形变可以较有效细化纯铜晶粒尺寸,交叉模压10道次后,平均晶粒尺寸减小63%;材料在塑性变形初期(2道次)细化效果最明显,经相同道次交叉模压形变后,晶粒细化效果逐渐减低;交叉模压变形后纯铜试样的显微硬度和抗拉强度均得到显著提高,但是伸长率下降,硬度值和抗拉强度分别提高了96.4%和31.9%,伸长率由66.67%下降至12.25%。     

Evolution of the structure and mechanical properties of sheets of the Al–4.7Mg–0.32Mn–0.21Sc–0.09Zr alloy due to deformation accumulated upon rolling

The mechanical properties and microstructure of sheets of an Al–4.7Mg–0.32Mn–0.21Sc–0.09Zr alloy deformed and annealed after rolling have been investigated. The total accumulated true strain was ε_f = 3.33–5.63, and the true strain at room temperature and at 200 °C was ε_с = 0.25–2.3. The strength properties of the sheets (yield stress σ_0.2 = 495 MPa and ultimate tensile strength σ_u = 525 MPa) in the deformed state were greater than those after equal-channel angular pressing (ECAP) deformation. The mechanical properties of the deformed sheets after annealing depended on the size of subgrains inside the deformed grains bands with high-angle grain boundaries (HABs). With the increase in the annealing temperature from 150 to 300°С, the subgrain size increased from 80 to 300 nm. The relative elongation δ in the as-cast state and after annealing at 200–250°C (δ = 40–50%) was higher than that after annealing at 300–370°C (δ = 24–29%).     

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 研究了冷轧00Crl2Ti汽车用铁素体不锈钢的试验钢板的再结晶晶粒显微织构、晶界角度分布和晶粒尺寸及其与力学性能的关系,采用两种不同保温时间的工艺退火试制出退火样,将退火样品首先经线切割、研磨和抛光制备成金相试样,然后,在光学显微镜观察两种退火工艺下的晶粒大小;同时采取EBSD技术扫描获取晶粒取向与亚结构分布图。试验结果表明：两种退火工艺钢板再结晶晶粒的显微织构、晶界角度分布和晶粒尺寸上存在着差异,这种差异印证出两种退火工艺钢板力学性能的差别。此外,利用EBSD还对两种退火工艺的再结晶程度作了分析。     

Influence of different rolling routes on mechanical anisotropy and formability of commercially pure titanium sheet

Influence of three different rolling routes on mechanical anisotropy and formability of commercially pure titanium sheet was investigated. Route A and Route B are unidirectional rolling (UR) where the rolling direction is along initial rolling direction (RD) and transverse direction (TD), respectively. Route C is cross rolling (CR) where the rolling direction is changed by 90° after each rolling pass. The microstructure and texture, tensile mechanical properties including strength and elongation, and also the anisotropy of the UR and CR sheets were investigated at room temperature. The XRD results indicate that the texture intensity of rolled samples gradually weakens from Route A to Route C. Compared with Route A and Route B rolled samples, the Route C rolled samples show a smaller planar anisotropy. The deep drawing tests reveal that cross rolling can avoid the occurrence of earing. Erichsen tests indicate that rolling routes have an effect on stretch formability of pure titanium sheet.     

关于锥形辊穿孔机的穿孔原理及应用问题的讨论

论述了二辊斜轧锥形辊穿孔机的穿孔原理及其应用范围。指出最大限度地抑制孔腔的发生,消除孔腔,不是二辊斜轧穿孔合理工艺追求的目标。通过对轧辊辊型的对比,认为二辊斜轧桶形辊穿孔机和二辊斜轧锥形辊穿孔机一样,也能适应连铸坯直接穿孔和高合金钢(包括部分难变形合金)制管的要求。     

Heterogeneity of Structure in Rolling and Annealing of Aluminum Alloys

Structure and special features of structure formation in aluminum and its alloys are studied for processes of cold rolling and annealing. Texture in various sections of sheets is studied after rolling with reduction of 8 – 70% and subsequent annealing at 300 – 550°C by x-ray survey of forward and backward pole figures. Fractions of recrystallized grains with different orientations and grain size distribution are evaluated by the x-ray rocking curve method. The obtained experimental data are analyzed from the standpoint of heterogeneity of the processes of deformation, segregation of intermetallic phases, and grain growth in annealing.     

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针对AZ31镁合金板材室温冲压成形较差的特点,采用在不同轧制温度下获得的镁合金板材对其进行拉伸、埃里克森和锥杯试验,并通过光学电镜和X射线衍射仪对其显微组织、织构和成形性能等进行研究.结果表明,AZ31镁合金板材的综合力学性能不仅与晶粒尺寸有关,还与晶粒取向有关;基面织构的减弱可明显提高板材的胀形性能,在基面织构强度相似的强况下,晶粒大小对板材的成形性能起决定性影响.     

Effect of Vibromechanical Treatment on the Properties and Structure of Aluminum Alloy AK8

The effect of vibromechanical treatment on the microstructure, strength, and ductility of aluminum alloy AK8 is described. The structure of the alloy in the initial and deformed states is investigated by the methods of metallographic and x-ray diffraction analyses. The mechanical properties of the alloy in tensile tests and the hardness are determined.     

Effect of Radial–Shear Rolling on the Formation of Structure and Mechanical Properties of Al–Ni and Al–Ca Aluminum–Matrix Composite Alloys of Eutectic Type

Results of an analysis of the mechanical properties and macro- and microstructures and the fractographic analysis of the fractures of samples of the Al–6 wt % Ni and Al–7.6 wt % Ca aluminum–matrix composite alloys of eutectic type after thermomechanical treatment, including radial–shear rolling (RSR),—have been presented. The hot deformation of preliminarily annealed ingots of studied alloys with a circular section 60 mm in diameter using RSR method at 400–450°C with total reduction μ = 9.0 can lead to the formation of the gradient microstructure with external more deformed layer characterized by high microhardness and thickness of about 1.5–2.5 mm. The microhardness decreases smoothly from the periphery to the center of samples. Uniaxial tensile tests revealed that the strength of alloys after RSR increases by 2.0–2.5 times compared to the as-cast or the annealed state, the plasticity is the same as in the annealed state or increases by several times as in the case of the Al–7.6 wt % Ca alloy. The latter fact is clearly illustrated by the results of the analysis of the fractures of samples, for which the transition from the brittle or mixed type of the fracture before deformation treatment to the pronounced ductile dimpled type after RSR has been observed.