Deformation Temperature Range Research Articles

On the influence of iron and silicon content on the phase composition of the Al-Fe-Si system

Increasing interest in intermetallic phases of the Al-Fe-Si system is associated with their high specific strength, corrosion and wear resistance, as well as the low cost of their production. To exhibit the most successful combination of properties, it is necessary to impart a specific compact morphology to the precipitated intermetallic phases. It is important to create an alloy with a composition capable of accepting plastic deformation. The purpose of the work is to develop the composition of an Al-Fe-Si system alloy capable of withstanding plastic deformation and determining the corresponding deformation interval. Based on computer modeling, an alloy composition capable of accepting plastic deformation was developed and the corresponding deformation interval was determined. The simulation was carried out in the ThermoCalc software package, TCAL8 database. It has been revealed that alloys with a high content of both silicon and iron are not characterized by the formation of a single-phase region, however, with a certain combination of alloy components, it is possible to achieve a quasi-single-phase structure, when the content of one phase is observed to be more than 90%. The solidus temperatures for different alloy compositions and the boundary conditions for the existence of phases have been determined. The α phase is present in the system from a temperature of 770°C up to a temperature of 446°C. In composition, it is found in the range from 5 to 35% iron with an amount of silicon of 10% and from 0 to 15% silicon with an iron content of 30%. The maximum amount of α phase was obtained for the Al60-65 alloy; Fe30-32; and Si5-10%, deformation temperature range is 600-450°C. Deformation in this region will ensure processing in a quasi-single-phase region without melting.

Hot deformation behaviors and microstructure evolution of a supersaturated nickel-based superalloy

The hot deformation behaviors and microstructure evolution of a supersaturated Ni-based superalloy GH4742 were investigated by isothermal compression tests. The deformation temperature range encompassed γ' sub-solvus (1000–1075 °C) and super-solvus (1100–1150 °C), with strain rates ranging from 0.001 s−1 to 1 s−1. Separate Arrhenius-type constitutive equations were established considering the re-precipitation of the γ' phase. The correlation coefficient between the calculated stresses and the experimental data was as high as 0.997, which indicated that the rheological behaviors of the material during hot deformation processes could be accurately analyzed by the constitutive relationship. Additionally, the activation energies for the γ + γ' two-phase region and the γ single region were calculated to be 949.08 kJ.mol−1 and 437.66 kJ.mol−1, respectively. Microstructural analysis revealed that the partial dynamic recrystallisation (DRX) occurred in the γ' sub-solvus regime whereas the full DRX occurred in the γ' super-solvus regime. The low DRX fractions in the γ' sub-solvus regime were attributed to the presence of near-spherical re-precipitated γ' phase, which effectively suppresses the nucleation and growth of new grains. The deformed grains were oriented in the <101> direction parallel to the compression direction. Meanwhile, the non-monotonic relationship between the degrees of DRX and strain rate was observed due to the adiabatic temperature rise. The retarding effects of solute elements on the grain growth in the γ' super-solvus regime were determined by comparing the recrystallized grain sizes from theoretical analysis and experiment values. This work can provide guidance for understanding the deformation behaviors of the alloy and achieving desired microstructures.

ОСОБЛИВОСТІ НЕОДНОРІДНОСТІ ПЛАСТИЧНОЇ ДЕФОРМАЦІЇ ГЕТЕРОФАЗНИХ НЕМЕТАЛЕВИХ ВКЛЮЧЕНЬ В СТАЛЯХ

The nature and level of plasticity of microcomposite heterophase inclusions in steels under pressure treatment condition was investigated. Plastic phases in heterophase inclusions of various types under the conditions of hot and cold deformation of steels were investigated. It is shown that each type of inclusions, which are microcomposite formations in steels, is characterized by its own laws of the development of deformation processes, which are determined by their chemical and phase composition, structure, deformation capacity of inclusion phases. The generalized of the plastic behavior of heterophase inclusions of various types with a complex structure have been established and inhibitory effect of non-deformable inclusion phases on the behavior of plastic phases in a wide range of deformation temperatures of steels has been established. The peculiarities of the nature of plasticity of heterophase inclusions with different compositions and structures are discussed. The use of the obtained results will make it possible to develop technologies for obtaining steels with a regulated content and types of heterophase non-metallic inclusions, which will significantly increase their technological plasticity, as well as prevent the formation of various types of defects during pressure treatment of steels.

Thermal Mechanical Behavior and Microstructure Characteristics of As‐Cast FeCrNiAl Steel

To find the suitable deformation temperature range for the as‐cast Fe–5.5Cr–5.5Ni–3.0Al–0.27C high‐strength lightweight steel, the thermal mechanical behavior and the dependent microstructure characteristics are studied to investigate the high‐temperature mechanical response of the steel. In the results, it is shown that the microstructure of the steel owns a dendrite framework consisting of the martensite dendrite and the interdendritic austenite, among which precipitations of NiAl, Ni3Al, and δ‐Fe are induced by high‐temperature deformation. The flow stress dependence of deformation temperature shows two different variation tendencies, corresponding to the varied deformation mechanisms of strain‐induced precipitation of second phases and δ‐Fe nucleation, and then resulting in different variation of dislocation density. It is found that a periodical fluctuation of flow stress appears as the alternative occurrence of first rise and then drop followed by drop and rise, and the phenomenon is inferred to be caused by local dynamic recrystallization in the dendrites and the neighboring interdendritic spacings.

Effect of hydrogen on thermal deformation behavior and microstructure evolution of MoNbHfZrTi refractory high-entropy alloy

The study examined the thermal-deformation behavior of an MoNbHfZrTi refractory high-entropy alloy (RHEA), which were hydrogenated using a liquid hydrogenation method and then subjected to high-temperature uniaxial compression in the deformation temperature range of 1100–1250 °C and strain rate range of 0.5–10−3 s−1. Test results showed that: (1) When the deformation temperature was between 1100 and 1250 °C, hydrogen addition led to increased high-temperature peak stress of the alloy at higher strain rates of 0.5 and 10−1 s−1. At a low strain rate of ∼10−2 s−1, the addition of hydrogen causes a decrease in the high-temperature peak stress. However, at a lower strain rate of ∼10−3 s−1, hydrogen addition has insignificant effects on the high-temperature peak stress. (2) At a higher strain rate of ∼0.5 s−1, the major reasons for hydrogen-induced hardening of the peak stress were solution strengthening and dislocation pinning. (3) At a low strain rate of 10−2 s−1, the reason for decrease of the peak stress was that the hydrogen addition promoted the formation of precipitated phases, thereby facilitating dynamic recrystallization (DRX), and making the microstructure more uniform at high temperatures.

Study on the precipitation behavior of the hot deformed 2195 Al–Li alloy after online quenching and its relation to the age-hardening response

The fine-grained structures following deformation would be retained by using online quenching treatment which would achieve the purpose of simplifying formation process and reducing energy consumption. This study examined the effects of hot deformations on grain morphology, dynamic precipitation behavior and age-hardening response of the alloy after online quenching. And the dynamic precipitates re-solution behavior after online assisted heating were analyzed. The results indicated that the age-hardening response of the alloy was primarily controlled by the deformation temperature, and the appropriate deformation temperature range for online quenching was determined as 475–500 °C. Most of the deformed grains exhibited <110>Al//CD orientation. The increase in deformation temperature induced the transformation of the deformed grains from <110>Al//CD to <100>Al//CD orientation. A number of coarse second phases would be observed when the alloy was deformed below the optimal temperature range (e.g. 450 °C). For this case, it was suggested that the deformed alloy was heated by online assisted heating for a short time with the remaining heat after hot deformation, promoting most of the dynamic precipitates to be re-dissolved before online quenching. As a result, the deformation temperature window suitable for online quenching in 2195 Al–Li alloy could be broadened to 450–500 °C.

Constitutive Modeling for Flow Stress and Processing Maps of a 0.2C–2.0Mn–0.5Cr Microalloyed Steel

Low‐carbon microalloyed steel with the microstructure of bainite is frequently utilized to produce automotive parts. The systematic investigation of the hot deformation behavior can serve as a reference for the optimization of deformation process parameters. The hot deformation of 0.2C–2.0Mn–0.5Cr microalloyed steel is studied. Based on the stress–strain curve, an Arrhenius model with strain compensation is established. The correlation coefficient R2 and the average absolute relative error calculated according to this model are 0.962 and 4.871%. The microstructure evolution at the strain of 0.90 is studied. In the stable region with substantial power dissipation, the microstructure is uniformly fine. The strain rate is high in the stable region with low‐power dissipation, and the room‐temperature microstructure after deformation retains a large amount of deformation storage energy and fine substructures. During deformation, the banded structures are formed in the instable region. The difference in dislocation density between the band structure and the nearby regions promotes the formation of necklace microstructures. Therefore, the 0.2C–2.0Mn–0.5Cr microalloyed steel has an ideal deformation process window in the range of a hot deformation temperature of 880–920 °C and a strain rate of 0.1–0.3 s−1.

Dependence of Electrochemical Characteristics of a Biodegradable Fe-30Mn-5Si wt.% Alloy on Compressive Deformation in a Wide Temperature Range

Fe-30Mn-5Si alloy subjected to a compression test at various deformation temperatures ranging from 350 to 900 °C with a strain rate of 1 s−1 are studied. It was found that the Fe-30Mn-5Si alloy exhibits high resistance to the dynamic recrystallization process in a whole studied range of deformation temperatures. There are no differences in structure formation in the zone of action of tangential tensile stresses and peripheral and central zones of localized compressive stresses. The room-temperature X-ray diffraction study shows the presence of a single-phase state (FCC γ-austenite) after deformation temperature range from 350 to 700 °C and a two-phase state (FCC γ-austenite + HCP ε-martensite) after deformation test at 900 °C. The presence of a two-phase state provides a higher rate of biodegradation compared with a single-phase state. The changes in the biodegradation rate dependence on the structure change with an increase in the deformation temperature are explained. Favorable temperature regimes for subsequent thermomechanical processing are proposed based on the relationship between structure formation and biodegradation rate to obtain semi-products from the Fe-30Mn-5Si alloy.

Constitutive Modeling of Hot Deformation Behaviors and Processing Maps of Mg–4.83Gd–2.36Nd–0.21Zr Alloy

Accurately assessing the hot workability and flow behavior is crucial in the preparation of high‐performance wrought Mg–rare earth (RE) alloys. The hot deformation behaviors and workability of Mg–4.83Gd–2.36Nd–0.21Zr alloy are examined via Gleeble 3500 thermosimulation tests across a range of deformation temperatures from 350 °C to 450 °C and strain rates ranging from 0.001 to 1 s−1. The experimental results reveal that the flow stress of the experimental alloy decreases as the temperature increases and the strain rate decreases. The activation energies for deformation (Q) of the experiment alloy are calculated by the hyperbolic constitutive equation and range from 186.78 to 234.97 kJ mol−1. Strain compensation is incorporated in constitutive modeling, resulting in the correlation coefficient (R) of 0.9865 and the average absolute relative error (AARE) of 5.4639%. Further, the processing maps are constructed at different strains based on dynamic material models, from which the feasible processing window of the experimental alloy is determined in the areas of deformation temperatures of 425–450 °C and strain rates of 0.01–0.1 s−1.

Dynamic recrystallisation behaviour and intrinsic workability of 12%Cr USC rotor steel during hot deformation

ABSTRACT Hot deformation of 12%Cr USC rotor steel was investigated by hot compression testing over a temperature range of 900 °C to 1,200 °C at strain rates of 0.001 s−1–1 s−1 with the use of a Gleeble–1500D thermal-mechanical simulator. The true stress–strain curves were obtained and showed that the stress increased with a decrease in temperature, an increase in strain rate, or both. Based on the stress–strain curves, processing maps of 12%Cr USC rotor steel under various strains were established, and the Zener-Hollomon (Z) parameter was calculated, it increased with decreasing temperature or increasing strain rate. Combining the values of the Z parameter and the microstructure after thermal compression, it was found that dynamic recovery was the main softening mechanism at lnZ > 39.09, and dynamic recrystallisation (DRX) became the main softening mechanism at 39.09 > lnZ > 32.56. When lnZ < 32.56, DRX occurred completely, and a small amount of recrystallised grains formed. The deformed microstructures showed that 12%Cr USC rotor steel incurred a continuous dynamic recrystallisation mechanism, a discontinuous dynamic recrystallisation mechanism, and a geometric dynamic recrystallisation mechanism during the hot deformation process. The intrinsic workability of 12%Cr USC rotor steel was explored by analysing the processing maps. It was found that the best forging process parameters range of the material in the actual production process was a deformation temperature range of 1,100 °C to 1,200 °C and a strain-rate range of 0.01 s−1–0.1 s−1.

STUDY OF LOW-TEMPERATURE THERMOMECHANICAL BEHAVIOR OF THE Ti-18Zr-15Nb SUPERELASTIC ALLOY UNDER DIFFERENT TEMPERATURE-RATE CONDITIONS

The biomedical alloy Ti-18Zr-15Nb (at.%) with shape memory was subjected to a true deformation e = 0.7 in three different modes: in the temperature range from 20°C to 600°C at deformation rate ξ = 0. 1 s-1; at temperatures 250°C and 300°C with strain rates ξ = 0.1, 1 and 10 s-1; deformation at 300°C and strain rate ξ = 0.1 s-1 after annealing at 300°C (τ = 10, 60, 300, 600 and 1200 s). It is established that with increasing temperature the conditional yield strength σ0.2 continuously decreases, at that in the temperature range of deformation temperatures 250°С-300°С the increase of maximum stress σmax is observed. In the temperature range from 200°С to 400°С fluctuations are observed on the flow curves, the amplitude of which increases with increasing temperature. The change σ0.2 and σmax, as well as the presence of oscillations on the strain diagrams are connected with the course of dynamic strain aging accompanied by the release of excess ω-phase particles at temperatures 200°С - 400°С. Increasing the strain rate at temperatures of 250°С - 300°С has a strong effect on the deformation behavior of the alloy due to a significant increase in temperature during the deformation process. Thus, increasing the strain rate up to ξ = 10 s-1 leads to a stepwise decrease in stress, starting from e ≈ 0.3, after which the plastic flow curve acquires a wave-like form with a low frequency of stress fluctuations. The main phase after all modes of thermomechanical tests is the BCC β-phase. At annealing of 300°С and an exposure of more than 300 s weak ω-phase lines are observed, and at deformation after aging significantly broadened ω-phase lines are observed only after prolonged exposure (1200 s).

Analysis on the Key Parameters to Predict Flow Stress during Ausforming in a High-Carbon Bainitic Steel

Since flow stress is an important parameter in the processing and application of metallic materials, it is necessary to trace the flow stress during austenite deformation. Thermal compression deformation of austenite in a high-strength bainitic steel was conducted using a Gleeble-3500 thermo-mechanical simulator, within the deformation temperature range of 400 °C~900 °C. By analyzing the stress–strain curves and strain-hardening exponent, the effects of strain hardening and dynamic recovery on the dislocation density of the material during the thermal processing were considered in the present work. Based on the general form of the Kocks–Mecking–Estrin (KME) model, the effects of deformation temperature and strain on the key parameters of the model were clarified. Differing from other work which commonly terms m (strain rate sensitivity exponent) and k2 (dimensionless parameters for dynamic recovery) as constants, the current models consider the quantitative relationship between key parameters and deformation temperature and strain. The results show that m is an exponential function related to temperature and strain, which decreases with the increase in strain. Meanwhile, k2 is a temperature-dependent polynomial function that increases as the deformation temperature increases. Finally, a modified constitutive KME model was proposed to predict the austenitic plastic stress with strain. Using established m-ε and k2-T models, the predicted curves are in good agreement with the experimental measurements.

Fatigue life and failure mechanism of nylon 66 cord/rubber composites under wide temperature range

This work simulates the real harsh service conditions of Fiber-reinforced polymer composites (FRPC), and the dynamic adhesion and failure mechanism of nylon 66 (PA66)-reinforced natural rubber (NR) composites under large deformation and wide temperature range are deeply studied by comprehensive analysis of the interfacial adhesion evolution, microstructure and failure damage location of the composites, interfacial heating rate, and modulus ratio of PA66/NR. The failure mechanism of PA66/NR composites is interfacial debonding at −20 °C, 25 °C and 80 °C, whereas that at 120 °C is matrix cracks. Interestingly, at −20 °C, the crack expansion at the interface is slow, and the samples show two-stage damage during fatigue, resulting in the highest fatigue life. At 80 °C, the interface heating rate and modulus ratio of the PA66/NR composites is the lowest, and thus the fatigue life is higher than that at 25 °C and 120 °C. Keywords: fiber reinforced polymer composites, fatigue life, failure mechanism.

Hot working processing and microstructure characterisation of as-cast high manganese TWIP steel

ABSTRACT The hot compression of the as-cast Fe-21Mn-0.7C–0.1Si twinning induced plasticity (TWIP) steel was investigated at the deformation temperature range of 950–1100 °C and strain rates of 0.01–5 s−1, using a GleebleTM thermo-mechanical simulator, to determine the hot deformation behaviour and analyse the recrystallisation mechanism. The results showed that the flow curves were characterised by yield-point-elongation (YPE) and dynamic recrystallisation (DRX) as the principal restoration mechanisms. The activation energy (Q) was calculated to be 394.975 KJ mol−1, which implies that the recrystallisation is sluggish in the whole range of the deformation conditions. Furthermore, the processing maps were generated according to the dynamic material model (DMM). The processing map was subdivided into different domains for the microstructural observations. The ideal hot deformation parameters of as-cast high Mn TWIP steel were obtained in the deformation condition range of 1087–1098 °C/10−1.2-10−0.17 s−1. Moreover, the microstructure analysis revealed that the DRX grains were twinned and nucleated through the bulging mechanism at the serrated grain boundaries, accompanied by twin boundaries migration created in the DRX grains by growth accidents, which contributed significantly to the growth of the DRX.

Relationship between β→α dynamic transformation and dynamic recrystallization under thermomechanical coupling in Ti-5Al-5Mo-5V-1Cr-1Fe alloy

The thermal simulation compression tests of near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe were performed within the range of deformation temperatures of 710–860 °C and strain rates of 0.001–1 s–1. Based on electron backscatter diffraction (EBSD) characterization and analysis technology, the interaction between dynamic phase transformation (DPT) of β-to-α and dynamic recrystallization (DRX) under thermal-mechanical coupling is deeply and systematically explored. We clarify the effects of temperatures and strain rates on the orientation relationship during dynamic precipitation of α-phase within β grain interiors possessing special orientation. The results show that the intragranular α-phase precipitated on the subgrain boundaries near {001}β with a high degree of dynamic recovery (DRV) deviates more from Burgers Orientation Relationship (BOR) than the α-phase that precipitates near {111}β as temperature increases. The proportion of α-phase precipitated by strain-induced on β recrystallized equiaxed grains for the deviating angle from BOR (θBOR) in the range of 20°–30° increases to 40% with the increase of strain rates below 800 °C. In addition, the α-phase is dynamically precipitated on the grain boundaries with {110}β orientation, which undergoes continuous dynamic recrystallization (CDRX), exhibiting epitaxial recrystallization, namely {110}β//{0001}α. Furthermore, the morphology of grain boundaries α phase (αGBs) precipitated by strain-induced phase transformation (SIPT) on specific types of β grain boundaries (βGBs), as well as the crystallographic orientation relationship and variant selection effect between adjacent α-variant within β grains are elucidated. The orientation relationships between α variants in {111}β grain are related with each other by 50°–60°/<–12–10> and 60°–70°/<–48–43> rotation. The “necklace” αGBs of recrystallization exhibit mainly the rotation of 50°–70° around the 〈2–310〉 zone axis, while the adjacent α-variant in the grain interiors is mainly 60° or 90°/<12−30>. In summary, the study has contributed to a deeper understanding of the deformation behavior and DPT laws of β-to-αp in near-β titanium alloy, which lays a foundation for the optimization of the hot deformation process and mechanical properties.

Hot Deformation Behavior and Processing Maps of Pure Copper during Isothermal Compression.

In this study, pure copper's hot deformation behavior was studied through isothermal compression tests at deformation temperatures of 350~750 °C with strain rates of 0.01~5 s-1 on a Gleeble-3500 isothermal simulator. Metallographic observation and microhardness measurement were carried out of the hot compressed specimens. By analyzing the true stress-strain curves of pure copper under various deformation conditions during the hot deformation process, the constitutive equation was established based on the strain-compensated Arrhenius model. On the basis of the dynamic material model proposed by Prasad, the hot-processing maps were acquired under different strains. Meanwhile, the effect of deformation temperature and strain rate on the microstructure characteristics was studied by observing the hot-compressed microstructure. The results demonstrate that the flow stress of pure copper has positive strain rate sensitivity and negative temperature correlation. The average hardness value of pure copper has no obvious change trend with the strain rate. The flow stress can be predicted with excellent accuracy via the Arrhenius model based on strain compensation. The suitable deforming process parameters for pure copper were determined to be at a deformation temperature range of 700~750 °C and strain rate range of 0.1~1 s-1.

Evolution of hot processing map and microstructure of as-forged nickel-based superalloy during hot deformation

Nickel-based superalloy has excellent mechanical properties at high temperature. However, the high deformation resistance, narrow deformation temperature range and complex microstructure evolution of the alloy bring great challenge to the plastic deformation of the alloy. The microstructure evolution and hot deformation behavior of as-forged nickel-based superalloy were examined through thermal compression tests at 950–1150 °C and strain rates of 0.001–10 s−1 with true strain of 1.0. The stress-strain curve exhibited a yield stage under small strain, and it comprised dynamic recovery (DRV) and dynamic recrystallization (DRX) two types. Strain rate sensitivity (m) and power dissipation efficiency (η) were calculated, and hot processing map was generated in accordance with the Murty criterion, and the rate of strain and the temperature of deformation were obtained as 1100–1150 °C and 0.02–0.4 s−1, separately, based on the optimal hot processing parameters. The instability zone was primarily in the zone of high strain rates. As the temperature of deformation was risen or the rate of strain was decreased, the DRX grain size was increased, as indicated by the microstructure results. The main deformation mechanism varied from DRX to DRV, and, then to the shear band (SB), deformation band (DB), and flow localization (FL) as η was decreased. Moreover, continuous dynamic recrystallization (CDRX) at subgrains rotation and discontinuous dynamic recrystallization (DDRX) at grain boundaries were identified during thermal deformation.

Comparative Study on Hot Metal Flow Behaviour of Virgin and Rejuvenated Heat Treatment Creep Exhausted P91 Steel

This article reports on the comparative study of the hot deformation behaviour of virgin (steel A) and rejuvenated heat treatment creep-exhausted (steel B) P91 steels. Hot uniaxial compression tests were conducted on the two steels at a deformation temperature range of 900–1050 °C and a strain rate range of 0.01–10 s−1 to a total strain of 0.6 using Gleeble® 3500 equipment. The results showed that the flow stress largely depends on the deformation conditions. The flow stress for the two steels increased with an increase in strain rate at a given deformation temperature and vice versa. The flow stress–strain curves exhibited dynamic recovery as the softening mechanism. The material constants determined using Arrhenius constitutive equations were: the stress exponent, which was 5.76 for steel A and 6.67 for steel B; and the apparent activation energy, which was: 473.1 kJ mol−1 for steel A and 564.5 kJmol−1 for steel B. From these results, steel A exhibited better workability than steel B. Statistical parameters analyses showed that the flow stress for the two steels had a good correlation between the experimental and predicted data. Pearson’s correlation coefficient (R) was 0.97 for steel A and 0.98 for steel B. The average absolute relative error (AARE) values were 7.62% for steel A and 6.54% for steel B. This study shows that the Arrhenius equations can effectively describe the flow stress behaviour of P91 steel, and this method is applicable for industrial metalworking process.

Hot tensile deformation behavior and microstructure evolution of 7075 aluminum alloy sheet

The hot tensile deformation behavior of 7075 aluminum alloy sheet was studied using Gleeble-3800 thermal simulation machine at deformation temperatures of 400–475 °C and strain rates of 0.001∼1s−1. Microstructure evolution and fracture morphology were observed by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The hyperbolic sine model is used to establish the constitutive equation of the relationship between peak stress and Z parameter. The results show that the hyperbolic sine Arrhenius constitutive equation can well characterize the flow behavior of the studied alloy, and the hot deformation activation energy is 132.52 kJ/mol. The average relative error between the predicted and experimental values is only 4.58%, and r2 is as high as 0.988, indicating that there is good consistency between the experimental value and the predicted value. When the strain rate keeps unchanged, the elongation of the studied alloy shows an upward trend in the lower deformation temperature range (400–425 °C). When the deformation temperature continued to rise to 475 °C, the elongation of the studied alloy decreased sharply. Based on the analysis of fracture morphology, a large number of dimples can be observed at 450 °C/0.001s−1, which is a typical ductile fracture. With increasing of deformation temperatures, the fracture mechanism gradually changes from ductile fracture to brittle fracture. Under the condition of 425 °C/0.01s−1, there are a lot of dislocations in the alloy, and the dislocation walls are formed. With the increase of deformation temperatures or the decrease of strain rates, the dislocation density gradually decreases and dynamic recrystallization occurs. The softening mechanism of the studied alloy changes from dynamic recovery to dynamic recrystallization.

Microstructure evolution and dynamic recrystallization nucleation mechanism of medium volume fraction SiCp/Al composite during hot deformation

In order to understand the microstructure evolution and the deformation mechanism of medium volume fraction SiCp/Al composite during hot deformation, the hot compression tests of 35 vol%SiCp/2024Al composite were investigated by Gleeble-1500D thermo-mechanical simulators over hot deformation temperatures range of 623–773 K and strain rate of 0.01–10 s−1. The microstructure in different deformation conditions were investigated utilizing OM, SEM and TEM. The results indicated that the flow stress, microstructure evolution, and the deformation mechanism are sensitive to deformation parameters, which can be represented by the Zener-Hollomon parameter (Z) in the hyperbolic sine equation. The softening mechanism, the degree of dynamic recrystallization, the average grain size, the size of precipitates, the dislocation density, and the nucleation mechanism of dynamic recrystallization of the experimental composite is associated with the Z parameter. The specific influence relationships are analyzed, and the interaction laws are obtained.