Thermomechanical Processing Routes Research Articles

Precipitation behavior of Al-Zn-Mg-Cu alloys with the coupled soft/hard micro-scale areas and its effect on properties

A novel thermomechanical processing route was developed to prepare Al-Zn-Mg-Cu alloys containing heterostructures with coupled soft/hard micro-scale areas. The heterostructure gives an effect on the subsequent precipitation behavior of alloys. Importantly, the tensile strengths, elongation and corrosion resistance of grain boundaries of the #3 alloy with an appropriate coupled distribution of soft/hard micro-scale areas are all greatly improved compared with the alloy with the homogeneous structure. Based on the detailed microstructure characterization, the corresponding strengthening and corrosion resistance mechanisms of alloys with heterostructure have been established in this paper.

Thermodynamic prediction and experimental verification of phase transformation kinetics in 3Mn steel with Ti and V microadditions

AbstractIn this work, the phase transformation kinetics and precipitation processes were studied using thermodynamic calculations and a dilatometric method to determine the optimal chemical composition of medium-Mn steel and its initial parameters of heat treatment. The investigated steel is intended for forgings with the microstructure composed of bainitic matrix and retained austenite (RA). An influence of Al and Si on the Ms temperature was characterized to obtain the best chemical composition in terms of RA stabilization. Theoretical continuous cooling transformation (CCT) and time–temperature transformation (TTT) diagrams were determined and compared with dilatometric results. Microstructural observations were compared with the dilatometric results. The hardenability of steel was high due to increased Mn and Mo additions. A very small fraction of cementite is expected in the microstructure due to Al and Si additions. The shortest time to start and finish the bainitic transformation was noted for the isothermal heat treatment at 420 °C. The completion of the bainitic transformation took about 25 min and is acceptable from the industrial point of view. The obtained results constitute a good basis for designing thermomechanical processing routes of bainitic steels with RA.

Greatly improved room temperature formability of Al-Zn-Mg-Cu-Fe alloy sheets via coupling distribution of domains with different strengths

Using high strength Al-Zn-Mg-Cu-Fe alloy sheets as structural parts is capable of realizing lightweight of automobiles, but the low room temperature formability seriously limits their widespread use in automotive industry. In this study, we propose a new strategy to construct the coupling distribution of domains with different strengths by an innovate short-flow thermomechanical processing route. Both the compatible deformation capacity and room temperature formability of alloy sheets can be greatly enhanced by the coupling action of dislocations with domains. Finally, the average plastic strain (r̅-value) of alloys with a suitable coupling distribution of domains with different strengths can be greatly increased to 0.7171, which is a great outclass as those of traditional Al-Zn-Mg-Cu alloy sheets. Furthermore, the evolution mechanisms of domains with different strengths and the coupling action mechanisms of dislocations with domains have been discussed in detail.

Effects of aging on the microstructure and mechanical properties of metastable β-type Ti-23.6Nb-5.1Mo-6.7Zr alloy with low elastic modulus

In this study, the influence of thermomechanical treatments on the microstructure and mechanical properties of a new metastable β-titanium Ti-23.6Nb-5.1Mo-6.7Zr alloy was assessed. The objective was to determine if the alloy is a potential candidate for a future fabrication of orthopedic implants, in particular prosthetic hip stems with a functional gradient of mechanical properties. Two thermomechanical processing routes were investigated: (a) 90% cold-rolled, (b) 90% cold-rolled, followed by annealing at 950 °C for 1 h. After these initial processing steps, samples were aged between 300 °C and 500 °C from 0.5 h to 4 h. Microstructural characterization was conducted by optical microscopy, transmission electron microscopy and x-ray diffraction. Young's modulus and microhardness were measured. Young's modulus of the sample annealed after cold rolling is lower than that after the cold rolled one. Aging was effective at increasing hardness but also increasing Young's modulus. The hardening during aging resulted from fine ωiso and α precipitation. The transmission electron microscopy investigations indicated that an aging treatment at 500 °C leads to a fine (α + β) microstructure, avoiding brittle ωiso precipitation. For these reasons, this alloy is a potential candidate for the manufacture of a hybrid hip prosthetic stem by employing localized aging treatment at 500 °C in the neck region, creating a functional strength gradient and maintaining a low Young's modulus in the distal part, which is needed to mitigate the stress shielding of the bone.

Reciprocating wear behavior of multi-directionally forged and aged Al-Cu-Li alloy

Al-Cu-Li alloys have drawn attention because of their decreased density, which is a result of the growing need for lightweight material systems in aerospace and aircraft applications. The alloy was subjected to multi-directional forging (MDF) and post-MDF artificial aging. Reciprocating sliding wear tests were conducted to investigate the effects of these processes on wear properties under different load conditions. After MDF, a decrease in wear resistance was noticed, on the other hand, 12 pass MDF treated samples showed improved wear resistance upon aging treatment. Wear scars and counter ball surfaces were examined using scanning electron microscope (SEM) to understand the wear mechanism and wear mode. The findings demonstrated that, at lower loads, adhesion and abrasion were the main wear processes; at greater loads, delamination, adhesion, and abrasion were clearly visible. The study revealed that the MDF and subsequent aging have a substantial effect on the wear behavior of Al-Cu-Li alloy and is an effective thermomechanical processing route to enhance wear resistance.

Effect of thermomechanical processing on mechanical properties and microstructural evolution of Al-Mg-Zn alloy

This study investigates the impact of thermomechanical processing route on the microstructural evolution, and mechanical properties (tensile strength, hardness and elastic plastic (J1c) fracture toughness) of the 7075-aluminum alloy. As received 7075 Al Alloy underwent for the solution heat treatment (SHT) followed by artificial aging and cold rolling (CR) process, respectively. Generally, it was observed that cold rolling of 7075 Al alloy is very challenging, but in this work 90 % cold rolling successfully achieved by optimizing the thermo-mechanical process. The novel heat treatment process for achieving the 90 % cold rolling reduction as follow: firstly, SHT was performed at 470°C for 8 hours(h), there after aging at 140°C for 21 h was performed. Characterization techniques like X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) was employed to assess the microstructure and phase constituents. Elastic plastic (J1c) fracture toughness was studied well on SHT, peak aged and rolled sample. Additionally, Vickers hardness and tensile test were performed. Aging and Cold rolling treatment effectively enhanced tensile strength and hardness ascribed to formation of fine rod shape precipitates of η"(Mg2Zn3) and formation of sub grains with localized strain accumulation, respectively. Split diffraction spots with satellite pattern in long range ordering has also observed in selected area electron diffraction (SAED) pattern of η" attributable to stacking faults and periodic arrangement of precipitates, respectively, as a consequence of this 90 % cold rolling of 7075 Al alloy was accomplished. The maximum Vickers hardness, Tensile strength and Elastic plastic (J1c) fracture toughness values were achieved after SHT (470°C for 2 h), peak aged (PA) (140°C for 21 h) and 90 % cold rolling are 226 HV, 526 MPa and 344.54 kJ/m2, respectively.

Coordinated deformation mechanisms of high formability Al–Mg–Si–Cu–Zn–Fe alloys via coupling control of thermomechanical processes

Both the high formability and strengths are greatly important for the automotive application of Al–Mg–Si–Cu alloys. In the present work, four novel thermomechanical processing routes were designed to improve the comprehensive properties of Al–Mg–Si–Cu–Zn–Fe alloys. The results show that, the interspace between Fe-rich particles and Fe/Mn-containing dispersoids can be significantly reduced by an optimized thermomechanical processing route. This enhanced the interaction between them during subsequent cold rolling process, resulting in increased number density and uniform distribution level of multi-scale Fe-rich particles, which further substantially improve both the recrystallization microstructure and mechanical properties, i.e., higher bendability, average r value of 0.72 (0.59 for traditional sheet) and tensile strength of 302 MPa (283 MPa for traditional sheet). The microstructure evolution of alloy sheets was schematically illustrated, and in-depth analysis on the mechanism of high formability was proceeded from the aspects of grain boundary misorientations and recrystallization texture.

Optimizing Thermomechanical Processing Routes to Achieve Desired Grain Size in SS 304 Using Response Surface Methodology

Optimizing Thermomechanical Processing Routes to Achieve Desired Grain Size in SS 304 Using Response Surface Methodology

Progress in the Optimization of Compositional Design and Thermomechanical Processing of Metastable β Ti Alloys for Biomedical Applications.

Over the past few years, significant research and development in the manufacturing industry related to the medical field has been done. The aim has been to improve existing biomaterials and bioimplants by exploring new methods and strategies. Beta titanium alloys, known for their exceptional strength-to-modulus ratio, corrosion resistance, biocompatibility, and ease of shaping, are expected to play a crucial role in manufacturing the next generation of biomedical equipment. To meet the specific requirements of human bone, researchers have employed key techniques like compositional design and thermomechanical processing routes to advance biomaterial development. These materials find extensive applications in orthopedic, orthodontic, and cardiovascular biomedical implants. Several studies have shown that precise material composition, with appropriate heat treatment and suitable mechanical approaches, can yield the desired mechanical properties for bone implants. In this review article, we explore the evolution of alloys at different stages, with a particular focus on their preparation for use in biomedical implants. The primary focus is on designing low-modulus β Ti alloy compositions and employing processing techniques to achieve high strength while maintaining a low young modulus suitable for biomedical applications.

Development of novel low density ultra-high strength manganese-steel with significant ductility through thermo-mechanical processing route

The development of ultra-high strength steels for automotive applications is often associated with insufficient ductility or formability properties. To overcome this problem, a high Mn alloy steel (Fe–15Mn-0.17C–2Al–3Si-0.6Ti) was prepared by induction melting and was subjected to various thermomechanical treatments (TMT) to achieve high strength with high ductility. The TMT comprised of simply hot forging (at 1373K) and hot rolling at three different temperatures (1073K, 1173K, and 1273K) followed by water quenching. The forged steel displayed a tensile strength of 510 MPa with 34 % elongation, while the hot-rolled steel (at 1173K) demonstrated a remarkable improvement in both strength (approximately 2 GPa) and ductility (around 51 % elongation). The microstructure of the rolled steel showed austenite, α-ferrite, and precipitates of TiAl; the austenite was found to possess finer grain size (∼7.9 μm) with a significant amount of twins (volume fraction = 32 %). The high strength was achieved due to finer grain size, higher amount of twins, transformation-induced martensite, and precipitation hardening, while the substantial ductility was attributed to significant TWIP and TRIP effect.

Construction of multiscale secondary phase in Al0.25FeCoNiV high-entropy alloy and in-situ EBSD investigation

Developing high-entropy alloys (HEAs) faces challenges owing to the inherent strength-ductility trade-off. This study systematically investigated the microstructure and mechanical properties of Al0.25FeCoNiV face-centered cubic (FCC) and body-centered cubic (BCC) duplex HEA, subjected to 70% cold rolling and annealing at various temperatures. The mechanism of the nonlinear effect of the annealing temperature on precipitation in duplex HEA was investigated. An economical and efficient thermo-mechanical processing route was developed to construct a multiscale BCC secondary phase. After 70% cold rolling and annealing at 1373 K, the yield strength (YS), ultimate tensile strength, and fracture elongation were 750 MPa, 1169 MPa, and 46.5%, respectively. This demonstrates superior strength-ductility coordination. In-situ electron backscatter diffraction (EBSD) tensile experiments were performed using a self-designed device to observe the dynamic evolution of the grain orientation and grain boundary distribution under diverse strain conditions. The influence of the multiscale BCC secondary phase on the mechanical properties was comprehensively investigated. The findings suggested that the exceptional mechanical performance was attributed to the coupled mechanism of multistage hetero-deformation-induced (HDI) strengthening and strain hardening produced by the multiscale BCC phase. Quantitative calculations revealed that the HDI strengthening (420 MPa) contributed over 50% to YS. This study lays a solid theoretical foundation for optimizing process parameters and innovating high-performance HEAs for engineering applications.

Impact of intermediate aging on the evolution of microstructure and intermetallics in thermomechanically processed Al-Cu-Mg alloy

Various thermomechanical processing routes were applied to Al-Cu-Mg alloy to investigate the evolution of microstructure and intermetallics. The microstructure characterization primarily revealed Cu-rich (Al7Cu2(Fe,Mn)) and Fe,Mn-rich (AlCuMnFeSi) compounds. The analysis indicated that the processing significantly transformed the Cu-rich particles. The trend of changes in volume fraction demonstrated that intermediate aging effectively suppressed the nucleation of particles and retained the solutes within the aluminum. It is suggested that the transformation kinetics of intermetallics were substantially affected by the formation of particles during aging acting as diffusion barriers.

Effect of Controlled Thermomechanical Processing Routes on the Structural and Textural States of Low-Carbon Low-Alloy Steel

Effect of Controlled Thermomechanical Processing Routes on the Structural and Textural States of Low-Carbon Low-Alloy Steel

Precipitation/recovery kinetics and mechanical properties in rapidly solidified AA6005 AlMgSi sheets via thin strip casting: Effects of casting cooling rate and thermomechanical processing route

Rapidly solidified AA6005 Al-Mg-Si sheets produced via a novel Thin Strip (TS) casting route were characterized and compared with conventional Direct Chill (DC) counterparts for the evolution of microstructure (i.e., precipitation/recovery kinetics) and mechanical properties at various thermo-mechanical tempers. To get to 1 mm final gauge, the DC ingot was homogenized, hot and cold rolled, whereas the TS casting was only cold rolled. After solutionizing (the T4 temper), the final-gauge DC and TS sheets exhibited a similar aging response upon the T6 temper. However, upon artificial aging without solutionizing, termed TSH temper, the as-rolled TS sheets showed a better age hardening kinetics, as manifested in a larger volume fraction of precipitates (primarily β' in this case) and a higher yield strength than the DC sheets (285.1 ± 5.1 MPa vs. 195.2 ± 2.2 MPa, respectively). This was attributed to the higher cooling rates the as-rolled TS sheets experienced during casting; thereby a higher Mg/Si supersaturation in the matrix due to rapid solidification. The TS sheet with the TSH temper exhibited a comparable yield strength to that of the T6 temper, though at a reduced ductility (5.5 ± 0.6% vs. 11.8 ± 0.3% elongation, respectively). Despite with a reduced volume fraction of the hardening precipitates (as compared with the T6 temper), the yield strength of the TS sheet at the TSH temper was compensated for by a considerable amount of remaining cold work from the prior cold rolling stage. Finally, a yield strengths model for the TS-TSH material was developed.

Microstructural and Mechanical Analysis of Seamless Pipes Made of Superaustenitic Stainless Steel Using Cross-Roll Piercing and Elongation

The cross-roll piercing and elongation (CPE) is a forming process performed at high temperatures and high strain rates. The final product quality is strongly dependent on its microstructure. In this study, a finite element method (FEM) model was developed to better understand plastic deformation effects on microstructure during CPE and to analyze alternative thermo-mechanical processing routes. Specific models were used to simulate dynamic and meta-dynamic recrystallization (DRX and MDRX) for the processing of superaustenitic stainless steel (SASS). In addition, the CPE of SASS was investigated experimentally. The microstructure, mechanical properties, and chemical changes of the final product were assessed using optical microscopy, hardness testing, X-ray diffraction, and SEM-EDS. The results revealed higher temperatures and strain rates in the exterior area of the shell after piercing, and MDRX occurred in the whole thickness. However, an average grain size reduction of 13.9% occurred only in the shell middle and inner diameters. During elongation, the highest values of the strain rate and DRX were observed in the inner region, exhibiting a grain size reduction of 38%. Spread in terms of grain size and grain shape anisotropy was found to be less accentuated for tube samples as compared to the pierced shells.

Examining the effect of intermediate aging temperature on intermetallics, microstructure evolution, and recrystallization in a thermomechanically processed Al-Cu-Mg alloy sheet

In this research, distinct thermomechanical processing routes, encompassing primary annealing, cold rolling, intermediate aging, and final heat treatment have been devised. The primary goal was to explore the critical impact of short intermediate aging temperature on the evolution of intermetallic particles, microstructure evolution, thermal stability, and recrystallization in Al-Cu-Mg alloy samples. The findings demonstrated that while each thermomechanical step exerted a significant influence on the microstructure and particles' evolution, interestingly, the composition of particles remained relatively unaffected by the processing steps. Throughout the experimental procedures, two major intermetallic compounds, namely Al7Cu2(Fe,Mn) and AlCuMnFeSi were consistently identified. It was observed that intermediate aging successfully suppressed recrystallization implying the higher thermal stability of the aged samples. Analysis of the changes in the volume fractions of particles, their size distribution pattern, and samples’ hardness revealed an optimal aging temperature of 170 °C, i.e., at which the lowest volume fraction of particles (6.33 vol%) was obtained concurrently with the greatest hardness (thus the highest thermal stability), as well as the lowest recrystallized fraction, hence effectively establishing an equilibrium between activation energy of precipitation and thermally activated diffusion mechanisms.

Reversion of strain induced martensite to achieve high strength and ductility in AISI 304 L

This work presents an optimized thermo-mechanical processing route to produce ultrafine grained AISI 304 L stainless steel with enhanced strength. Here AISI 304 L was rolled to 93% thickness reduction at room temperature to form 70% strain induced martensite with the remaining phase being untransformed deformed austenite. Subsequently, this was subjected to a thermal treatment in the range of 650–750 °C with time ranging from 10 to 1440 min so as to revert the strain induced martensite to ultrafine grained austenite. The median grain size obtained after different reversion treatments varied from 0.42 to 1.2 μm. The major texture components observed after reversion at 650 and 700 °C were {110}〈112〉 Brass and {123}〈634〉 S, whereas those observed after reversion at 750 °C were {110}〈112〉 Brass, {123}〈634〉 S and {113}〈112〉 R. Tensile tests showed a higher strength (but lower ductility) along the transverse direction as compared to that along the rolling direction. The yield strengths obtained after reversions at different temperatures and times were correlated with grain size, dislocation density and texture. A combination of high tensile strength and good ductility was obtained in the rolling direction after reversion at 700 °C for 60 min (900 MPa and 45% ductility) and at 750 °C for 10 min (900 MPa and 55% ductility).

Designing ultrastrong and thermally stable FeCrAl alloys with the fine-grained structure

Designing microstructurally stable FeCrAl alloys with excellent strength-ductility synergy is highly desirable for their engineering applications. However, due to the preference nucleation of precipitates at grain boundaries (GBs), the improved precipitation strengthening of these alloys is usually accompanied by intergranular embrittlement. Here, we propose a novel thermomechanical processing route coupled with the Si alloying strategy via precipitation of coherent deformable Laves precipitates inside equiaxed fine-grains to achieve FeCrAl alloys with ultrahigh yield strength over ∼992 MPa, excellent uniform elongation of ∼7.6% at room temperature, and superior thermal stability at temperature ∼1200 °C. The Si alloying not only decreases the stacking fault energy of Laves precipitates favorable for their stacking-fault-mediated deformation but also hinders grain coarsening at 1200 °C due to the Si-enrichment favorable for GB pinning effects. Our results prove the possibility of achieving the collaborative enhancement of mutually exclusive properties in alloys, such as strength-ductility-thermal stability via nanoprecipitation engineering, and offer a promising route to prepare dispersion-strengthened materials.

In-situ investigation of damage mechanisms in duplex AlCoCrFeNi2.1 high entropy alloy

The AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA) is a promising casting system with high strength, and numerous studies investigating the effects of various thermomechanical processing routes. However, the ductility of this alloy – especially in its cast state – limits its practical applicability. In this paper, damage evolution and microstrain partitioning behaviour is presented along with bulk mechanical performance of the as-cast and hot rolled AlCoCrFeNi2.1 EHEA to provide experimental reasoning behind observed changes in ductility and strength. Tensile testing coupled with in-situ micro-digital image correlation (μ-DIC) and x-ray computed tomography (XCT) were used to determine the damage and fracture mechanisms. Microstrain analysis documents the effect of phase co-deformation and microstructure morphology on crack formation, and the role of damage evolution is supplemented with XCT. These results suggest methods to improve crack resistance in this alloy system and corroborate macroscopic mechanical property changes.

Excellent strength-ductility synergy in a novel medium manganese steel containing 2.4Al-2.9Mn-4.1Ni realized through limited thermo-mechanical processing steps

In this study, the effect of microstructural and micro-textural evolution on tensile properties in hot forged (HF) and hot rolled (HR) medium-Mn steel containing ∼4 wt% Ni is systematically investigated. The microstructures of HF and HR specimens comprise of martensite (α′), nanosized NiAl (B2) precipitates and retained austenite (RA). The excellent tensile properties in HF and HR specimens have been achieved through minimal thermomechanical processing routes. The HR specimen exhibits better strength (∼1868 ± 69 MPa), and ductility (∼16.5 ± 1%) as compared to the HF specimen (∼1765 ± 32 MPa, and ∼12 ± 2%). The prior austenite grain (PAG) size of HR specimen is lower than HF, leading to lower width of lath martensite which contributes to achieving higher strength in the former specimen. Apart from the lath width, the presence of twin martensite along with RA, higher fraction of high angle grain boundaries (HAGBs), and ∑3 boundaries improve the strength-ductility synergy in HR specimen as compared to HF condition. The development of higher intensity γ-fiber <111>//ND during hot rolling has resulted in better ductility in HR specimen, whereas the presence of high intensity Cube texture {001}<100> has deteriorated the tensile properties of HF specimen. Further, visco-plastic self-consistent (VPSC) simulation has been carried out to understand the influence of primary {110}<111> and secondary {112}<111> slip systems activation on strain hardening response of the specimens. It has been observed that the higher activation of primary slip system {110}<111> in HR specimen leads to better strain hardening response at stage IV as compared to HF specimen.