Microstructure and Mechanical Properties of Cryorolled Aluminum Alloy AA2219 in Different Thermomechanical Processing Conditions

Metallurgical and Materials Transactions A - In the present study, aluminum alloy AA2219-T87 bars were cryorolled to various amounts of deformation in two pre-deformation conditions: (1) without...     

Influence of Processing Severity During Equal-Channel Angular Pressing on the Microstructure of an Al-Zn-Mg-Cu Alloy

A commercial Al-Zn-Mg-Cu alloy, Al 7075, was overaged at 553?K (280?°C) for 5?hours and processed by equal-channel angular pressing (ECAP) using route B_C. Different temperatures and number of passes, which determine the processing severity, were considered. The processing severity has been estimated by the maximum stress (?? _Proc) recorded during each ECAP pass. The higher the number of passes or the lower the processing temperature, i.e., the higher is the processing severity, the finer the (sub)grain size is obtained. A minimum ultrafine (sub)grain size of approximately 150?nm after three passes at 353?K (80?°C) or eight passes at 403?K (130?°C) was obtained. The microhardness exhibited an instant increase from 76?HV for the overaged initial state to 115?HV after only the first pass. The coarsened precipitates in the overaged alloy lead to larger structural refinement than in pure aluminum.     

Recrystallization Phenomena During Friction Stir Processing of Hypereutectic Aluminum-Silicon Alloy

Microstructural evolution and related dynamic recrystallization phenomena were investigated in overlapping multipass friction stir processing (FSP) of hypereutectic Al-30 pct Si alloy. FSP resulted in the elimination of porosities along with the refinement of primary silicon particles and alpha aluminum grains. These alpha aluminum grains predominantly exhibit high angle boundaries with various degrees of recovered substructure and dislocation densities. The substructure and grain formation during FSP take place primarily by annihilation and reorganization of dislocations in the grain interior and at low angle grain boundary. During multipass overlap FSP, small second phase particles were observed to form, which are accountable for pinning the grain boundaries and thus restricting their growth. During the multipass overlap FSP, the microstructure undergoes continuous dynamic recrystallization by formation of the subgrain boundary and subgrain growth to the grain structure comprising of mostly high angle grain boundaries.     

Kinetics of Austenite Transformation During Thermomechanical Processes

Abstract

One of the most important fundamental problems of thermomechanical processing (TMP) of steel is the transformation kinetics of deformed austenite, which has a great influence on the final microstructure and mechanical properties. In the present work, the results of more than 20 year's systematic study of deformation effects on the ferrite-pearlite and bainite transformations conducted by the authors and their colleagues are discussed. The progress of isothermal austenite decomposition was measured by magnetometry, while dilatometry was used to monitor transformation under continuous cooling. From a research base of about 40 steel grades, general conclusions of the characteristic features of austenite transformation kinetics during TMP are formulated and the factors responsible for changes in the kinetics are discussed. The acceleration effects of deformation on the ferrite-pearlite transformation and the much more complicated variations in austenite decomposition rates in the bainite range are considered depending on deformation parameters (temperature (T), strain, postdeformation delays), transformation conditions, and carbon and alloying content of the steels.© 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier ScienceLtd. All rights reserved.

Résumé

L'un des problèmes fondamentaux les plus importants du traitment thermomécanique (TMP) de l'acier est la cinétique de transformation de l'austénite déformée, qui a une grande influence sur la microstructure finale et sur les propriétés mécaniques. Dans le présent travail, on discute des résultats de plus de 20 ans d'études systématiques par les auteurs et leurs collégues, des effets de la déformation sur la transformation en ferrite-perlite et en bainite. On a mesuré, par magnétométrie, le progrés de la décomposition isotherme de l'austénite, alors qu'on a utilisé la dilatométrie pour suivre la transformation en refroidissement continu. A partir d'une base de recherche d'environ 40 types d'acier, on formule des conclusions générales des points caractéristiques de la cinétique de transformation de l'austenite lors de traitement TMP et l'0n discute des facteurs responsables des changements de cinetique. On considére les effets d'accélération de la déformation sur la transformation en ferrite-perlite ainsi que les variations beaucoup plus compliquées destaux de décomposition de l'austénite dans le domaine de la bainite. Ces considérations incluent les paramètres de déformation (temperature (T), déformation, délais d'après-déformation), les conditions de transformation ainsi que le contenu en carbone et en éléments d'alliage des aciers. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.     

热镀铝-锌合金钢丝生产过程控制回路的设计

研制一种新型的助镀剂用于镀锌生产流水线中,便可对低碳钢丝进行热镀铝-锌合金。作者介绍了在国内现有的传统溶剂法热镀锌生产流水线上,用自动控制的方法代替原有人工检测和手工调节,以实现对整个生产线的温度、张力等工艺参数的自动检测与控制,达到稳定产品质量,避免人为误差,提高生产效率的目的,并详细论述了生产过程自动控制回路的设计。     

Viewpoint on the Formation and Evolution of Annealing Twins During Thermomechanical Processing of FCC Metals and Alloys

Metallurgical and Materials Transactions A - The question of the formation mechanism of annealing twins in face-centered cubic metals and alloys, which is still not resolved in spite of the fact...     

Texture Development in the Ni47Ti44Nb9 Shape Memory Alloy During Successive Thermomechanical Processing and Its Effect on Shape Memory and Mechanical Properties

For improving the shape memory performance and mechanical properties of shape memory alloys (SMAs), crystallographic texture and second phase are generally induced in SMAs by suitable thermomechanical processing. For this purpose, the development of texture in the Ni₄₇Ti₄₄Nb₉ SMA during successive processing (e.g., hot forging, hot rolling, cold rolling, and heat treatment) and the effects of texture, grain size, and β-Nb particle precipitation on recoverable strains and tensile properties were studied. In the hot-forged and hot-rolled Ni₄₇Ti₄₄Nb₉ alloy rods, intense 〈111〉 fibers are formed, and water quenching from 873 K and 1123 K (600 °C and 850 °C) leads to the decrease in intensity of 〈111〉 fiber in the hot-rolled rod. When the hot-forged rod is hot-rolled into sheet, intense {001} and weak {123} fibers appear, but grain growth leads to the disappearance of {001} fiber and {110}〈001〉 becomes the strongest component. Cold-rolling deformation of the hot-rolled sheet promotes the development of γ-fiber and the convergence of {332} and {123} fibers to {233}〈110〉 and {123}〈121〉 components, respectively, and the intense component is turned into {111}〈110〉; in this case, the recoverable strain (ε _SRS) and tensile yield strength (σ _YS ) exhibit an anisotropy. When the quenching temperature is 1123 K (850 °C), some weaker components appear, the anisotropy of ε _SRS disappears, and the difference level in σ _YS along the rolling direction (RD) and transverse direction (TD) becomes smaller. Therefore, an appropriate heat-treatment temperature should be selected to maintain the deformation texture and also to obtain fine grains for different thermomechanical processing.     

Ultrafine Grain Formation in a Ti-6Al-4V Alloy by Thermomechanical Processing of a Martensitic Microstructure

In the current study, ultrafine equiaxed grains with a size of 150 to 800 nm were successfully produced in a Ti-6Al-4V alloy through thermomechanical processing of a martensitic starting microstructure. This was achieved through a novel mechanism of grain refinement consisting of several concurrent processes. This involves the development of substructure in the lath interiors at an early stage of deformation, which progressed into small high-angle segments with increasing strain. Consequently, the microstructure was gradually transformed to an equiaxed ultrafine grained structure, mostly surrounded by high-angle grain boundaries, through continuous dynamic recrystallization. Simultaneously, the supersaturated martensite was decomposed during deformation, leading to the progressive formation of beta phase, mainly nucleated on the intervariant lath boundaries.     

The Effect of Concurrent Straining on Phase Transformations in NiAl Bronze During the Friction Stir Processing Thermomechanical Cycle

Equivalent strains up to a value of ≈2.7 were determined by evaluation of the shape changes of the phases in a duplex α(fcc)/β(bcc) microstructure formed ahead of the pin tool extraction site during the friction stir processing (FSP) thermomechanical cycle in a cast NiAl bronze alloy. Correlation of the local strains with volume fractions of the various microstructure constituents in this alloy shows that the concurrent straining of FSP results in acceleration of the α + β → β reaction in the thermomechanically affected zone (TMAZ) ahead of the pin extraction site. The resulting volume fraction of β (as determined by the volume fraction of its transformation products formed during post-FSP cooling) corresponds closely to the volume fraction expected for the peak stir zone temperature measured separately by means of thermocouples embedded within the tool pin profile along the tool path. The stir zone (SZ) in this material exhibits near-equilibrium microstructures despite brief dwells near the peak temperature (T _peak ≈ 0.95T _melt), reflecting large local strains and strain rates associated with this process.     

Grain Refinement of an Extruded Mg Alloy via Na Microalloying

The effect of 0.3 wt pct Na on the microstructure of extruded alloy Mg-2Sn-1Zn is examined. We report that Na stabilizes the Mg₂Sn phase, resulting in its precipitation during extrusion under conditions where a solid solution is otherwise expected. This effect appears to be thermodynamic in nature and is different from the kinetic enhancement of low- temperature aging reported by Mendis et al. [Phil. Mag. Letters, 86 (2006), 443]. The precipitates of the current study enable useful refinement of the grain size.     

形变热处理对Cu-0.1Fe-0.03P合金组织与性能的影响

成分为Cu-0．1％Fe-0．03％P（TFe0．1）的引线框架铜合金连续铸坯经热轧成厚15mm宽60mm的带坯，之后进行固溶-冷轧变形-时效处理和在线固溶-冷轧变形-时效处理，冷轧变形量为85％，90％和95％，在此基础上测试了合金的拉伸力学性能和电导率，用金相和透射电子显微分析研究了不同处理态合金的微观组织结构及其变化。结果表明，合金热轧后在线固溶-95％冷轧变形．500℃／2h时效处理是TFe0．1合金比较好的形变热处理工艺，在此条件下，合金的抗拉强度、屈服强度、延伸率和电导率分别为258，192MPa，22．5％和86．0％IACS，合金的显微组织结构为固溶体基体和弥散分布的第二相颗粒，析出强化和亚结构强化是TFe0．1合金强化的主要原因。     

The Effect of Thermomechanical Processing on the Tensile, Fatigue, and Creep Behavior of Magnesium Alloy AM60

Tensile, fatigue, fracture toughness, and creep experiments were performed on a commercially available magnesium-aluminum alloy (AM60) after three processing treatments: (1) as-THIXOMOLDED (as-molded), (2) THIXOMOLDED then thermomechanically processed (TTMP), and (3) THIXOMOLDED then TTMP then annealed (annealed). The TTMP procedure resulted in a significantly reduced grain size and a tensile yield strength greater than twice that of the as-molded material without a debit in elongation to failure (ε _f ). The as-molded material exhibited the lowest strength, while the annealed material exhibited an intermediate strength but the highest ε _f (>1 pct). The TTMP and annealed materials exhibited fracture toughness values almost twice that of the as-molded material. The as-molded material exhibited the lowest fatigue threshold values and the lowest fatigue resistance. The annealed material exhibited the greatest fatigue resistance, and this was suggested to be related to its balance of tensile strength and ductility. The fatigue lives of each material were similar at both room temperature (RT) and 423 K (150 °C). The tensile-creep behavior was evaluated for applied stresses ranging between 20 and 75 MPa and temperatures between 373 and 473 K (100 and 200 °C). During both the fatigue and creep experiments, cracking preferentially occurred at grain boundaries. Overall, the results indicate that thermomechanical processing of AM60 dramatically improves the tensile, fracture toughness, and fatigue behavior, making this alloy attractive for structural applications. The reduced creep resistance after thermomechanical processing offers an opportunity for further research and development.     

Effect of Interfacial Mn Partitioning on Carbon Partitioning and Interface Migration During the Quenching and Partitioning Process

A so-called QP-LE model, in which interface condition is assumed to be Local Equilibrium (LE), has been proposed to evaluate the effect of interfacial Mn partitioning on interface migration and carbon partitioning during the Quenching and partitioning process (Q&P) of an Fe-0.3C-3.0Mn-1.5Si (wt pct) alloy. The predictions by the QP-LE model are compared with those by the conventional QP-PE model in which interface condition is assumed to be Paraequilibrium (PE). It is found that interfacial partitioning of Mn plays a significant role in carbon partitioning and the martensite/austenite interface migration during the Q&P process.