Influence Of Pre-deformation Research Articles

Investigation on work hardening rate of Al-Zn-Mg-Cu alloy under solid solution process and thermomechanical coupled multi-step fast aging process

In this paper, the work hardening rate of Al-Zn-Mg-Cu alloy in the conditions of solid solution and thermo-mechanical coupled fast aging were investigated separately, and the main research content and results are as follows. Under the solid solution processes at different temperatures, the uniaxial tensile test curves of work hardening rate are relatively dispersed at a lower strain rate, and the work hardening rate increases with the increase of solution temperature. Then, as the strain rate increasing, the work hardening rate curves at each solution temperature gradually converge, until all curves intersect at a common intersection point. The above mechanism is attributed to the comprehensive effect of precipitates, solid solutions, and dynamic strain aging in the matrix. For the thermo-mechanical coupled aging, the work hardening rate has a great different with that of solid solution process. Consequently, the influence of pre-deformation on the work hardening rate were investigated, which concludes the curve shape type and the softening coefficient. The introduction of dislocation have some significant influences on the work hardening rate. Firstly, it makes the shape of work hardening rate curves change from shape 1 to shape 2. On the other hand, as the pre-deformation increasing, the variation law of softening coefficient shows an abnormal trend that is different from the ordinary law, which is due to the coordinated effect between dislocation density and dislocation induced precipitation. Furthermore, in order to reveal the internal mechanism in depth, the microstructure are observed by TEM (Transmission electron microscope). Finally, a targeted set of analytical models for work hardening rate were established, especially the mathematical explanation of the multicollinearity phenomenon of work hardening rate curves in the solid solution condition.

Effects of pre-deformation on microstructure, mechanical properties and corrosion performance of an Al-Cu-Mg-Ag alloys

The influence of pre-deformation on the microstructure, mechanical properties, and corrosion behavior of AA2029-T8 was investigated. The pre-deformation may potentially impede the formation of Mg-Ag clusters during the early stage of aging, altered the normal precipitation sequence of the alloy, and significantly increased dislocation density that facilitated non-uniform nucleation of S phase at dislocations, resulting in finer dispersion of precipitation. Moreover, it led to a decrease in Ω phase volume fraction and comparable aspect ratio(diameter/thickness). With increasing deformation, aging response was accelerated, leading to shorter time to peak strength but reduced plasticity. Additionally, the width of precipitate-free zone (PFZ) remained relatively unchanged with increasing pre-deformation; however, average size of grain boundary precipitates (GBPs) decreased while becoming more discontinuous. This resulted in narrowing intergranular corrosion (IGC) channels and decreased maximum corrosion depth as well as a transition from IGC to pitting corrosion behavior. These findings suggest that the mechanical properties and corrosion resistance of the alloy can be improved by increasing pre-deformation levels.

Fatigue Crack Propagation on Uniaxial Loading of Biaxially Predeformed Pearlitic Rail Steel

Rolling contact fatigue loading causes the surface material in the top of the rail to severely deform. The microstructure aligns along the shear direction and the mechanical behavior in terms of plastic flow becomes anisotropic. Cracks are initiated in the severely deformed surface region and propagates along the direction of microstructure flow lines. However, the effect of large shear deformation on fatigue crack growth is not yet well understood. In this study, uniaxial fatigue crack propagation of undeformed and biaxially predeformed pearlitic rail steel R260 has been investigated. The material was predeformed to different deformation states using combined axial compression and shear deformation, corresponding to material found at different depths in the severely deformed surface layer of rails. Fatigue crack propagation rate was dependent on the material state and influenced by both work hardening and microstructural anisotropy. It was found that predeformed material exhibited lower crack growth rates than undeformed material under this loading condition. The influence of predeformation on the crack growth direction was limited.

Influence of pre-deformation on microstructure and mechanical properties along thickness direction of 2519A Al alloy thick plate

2519A aluminum (Al) alloy is widely employed in the military industry due to its superior strength and anti-ballistic capabilities. However, its inferior mechanical properties along the thickness direction (normal direction of the alloy, ND direction) limit its further utilization in armored vehicles. To enhance the mechanical properties along ND direction of 2519A Al alloy, the microstructure and mechanical properties in ND direction of the alloy at 7–15 % pre-deformation were investigated. The result indicated that the average aspect ratio of the grains (ARGs) of the alloy gradually increased with the increase of pre-deformation, the degree of fragmentation of the coarsen secondary phase gradually increased, and the size and number density of θ′ phase first increased and then decreased. The strength and elongation of the alloy along ND direction were increased firstly and then decreased with the increase of pre-deformation. Especially, the elongation of the alloy decreases by 55 % at 15 % pre-deformation compared to 11 % pre-deformation. The elongation of the alloy is mainly affected by the ARGs and the spacing of the secondary phase. The best mechanical properties along ND direction were obtained at 11 % pre-deformation with yield strength and tensile strength of 448 MPa and 505 MPa, and elongation of 5.99 %, respectively.

Enhanced thermoplasticity of 7Mo-0.4 N contained super austenitic stainless steel through pre-deformation

This study investigated the hot tensile deformation behavior of super austenitic stainless steel (SASS) with different pre-deformation degrees within 1150–1250 ˚C. The influence of pre-deformation on the number of annealing twin (AT), grain size, dislocation evolution, sigma phase precipitation, static recrystallization (SRX), and dynamic recrystallization (DRX) behaviors at hot tensile deformation stages is analyzed. Results show that the thermoplasticity of the SASS increases first and then decreases with the increase of pre-deformation degree at each deformation temperature. The area reduction of the samples pre-deformed for 0 %, 10 %, 20 %, and 25 % are 0.25, 0.32, 0.37, and 0.35, respectively at a tensile temperature of 1150 ˚C. When the pre-deformation degree is within the range of 0–20 %, the deformation storage energy (DSE) gradually increases with the pre-deformation degree. The SRX amount at the high-temperature holding stage and the DRX amount in the high-temperature deformation stage significantly increases, and the grain size gradually decreases. As a result, crack initiation and propagation are inhibited, and thermoplasticity improves. However, when the pre-deformation degree is increased to 25 %, the grains grow abnormally during the high-temperature tensile deformation, and a large number of sigma phases are induced, which deteriorates the thermoplasticity of the SASS.

Influence of pre-deformation on fatigue life of high strength steels by means of micromagnetic Barkhausen noise

Abstract The micromagnetic Barkhausen noise as a nondestructive testing method was employed in this work to analyze the fatigue behavior of high-strength steels by subjecting them to multi-stage load increase fatigue tests. The micromagnetic Barkhausen noise energy (MBNEnergy) was measured during fatigue tests and coupled with digital image correlation to evaluate the effect of static and cyclic stress as well as local surface strain on MBNEnergy. The test samples were prepared from the forged bainite 18MnCrMoV6 and two ferrite-pearlite 38MnVS6 and 46MnVS5 steels. A part of the specimens was pre-strained before cyclic loading to analyze the effect of pre-deformation on cyclic strength considering measured MBNEnergy. A significant increase in MBNEnergy was observed by increasing the cyclic load on 18MnCrMoV6 specimens with bainite phases while this increase of MBNEnergy was not significant or was not changed for ferrite-pearlite steels 38MnVS6 and 46MnVS5.

Evolution of Microstructure and Mechanical Properties of Al-Zn-Mg-Cu Alloy by Extrusion and Heat Treatment

Herein, composite extrusion deformation and heat treatment process at various temperatures were studied on a new type of Al-Zn-Mg-Cu alloy billet. The influence of pre-deformation and the final forming of extrusion and heat treatment of annular channel corner extrusion on the microstructure evolution and mechanical properties were explored. The results show that the extrusion process could further refine the structure and break the coarse θ phase. The grains can be refined again after the deformed sample was treated by solution-aging treatment. At the same time, a fine, dispersed second phase is precipitated around the fine recrystallized grains. This is the main reason for the increase in alloy elongation and tensile strength. The best heat treatment process parameters for the formed cup-shaped structure are 480 °C × 1 h solid solution and 120 °C × 24 h aging. The strengthening of the alloy mainly includes three mechanisms: fine grain strengthening, precipitation strengthening, and dispersion strengthening.

Influence of pre-deformation on the precipitation characteristics of aged non-equiatomic Co1.5CrFeNi1.5 high entropy alloys with Ti and Al additions

Non-equiatomic Co1.5CrFeNi1.5 high entropy alloys (HEAs) with Ti and Al additions (Al0.5Co1.5CrFeNi1.5 – Al05, Al0.2Co1.5CrFeNi1.5Ti0.3 – Al02Ti03 and Co1.5CrFeNi1.5Ti0.5 – Ti05), aged at 750 °C, exhibit pronounced precipitation hardening. The present work investigates the effect of pre-deformation on their aging response, primarily focusing on the precipitation characteristics and their effect on strengthening. Pre-deformation of 25% through quasi-static compression has been applied on the solution treated HEA samples. The pre-deformed samples have been aged at 750 °C for different time intervals. Interestingly, pre-deformed HEAs have shown reduced peak-aging time of 50 h in all the three HEAs, due to the enhanced precipitation kinetics arising from the significant increase in their dislocation densities. Microstructural investigations on the pre-deformed and aged alloys show distinct precipitate size and distribution characteristics. The same has been quantitatively assessed to understand their role on aging response and coarsening kinetics during over-aging.

The Influence of Material Selection and Pre-deformation on the Perfor-mance of Foil Bearing

Material selection is one of the most important steps in the manufacturing process of foil bearing. In this study, an experimental work is carried out to study the effect of operating temperature on the damping coefficients and the elastic modulus of Inconel X-750 and SUS321. Then, the influence of pre-deformation on the damping coefficients and the elastic modulus of Inconel X-750 are discussed. Finally, this paper calculates the rotor trajectory supported by the foil bearing considering the different pre-deformation of the foil. The results show that for the foil bearing supporting the rotor system shown in this paper, the Inconel X-750 with 10% pre-deformation is the best choice.

Strategies to tailor serrated flows in metallic glasses

Abstract

Influence of pre-deformation on the precipitation of Cu-rich clusters in RPV model steel

The effect of pre-deformation on the precipitation process of Cu-rich clusters in reactor pressure vessels (RPV) model steel is studied. In this research, Fe-1.16wt%Cu binary alloy is selected as RPV model steel to simulate the precipitation process of Cu-rich clusters. The solid-solution Fe-Cu alloys were cold rolled with pre-deformation of 0, 10%, 25%, 40%, 60%, followed by aging at 450°C for a series time. The dislocation density, Vickers hardness and microstructure evolution of Fe-Cu alloys after aging were determined. It is revealed that the Vickers hardness of un-deformed specimens reaches to peak hardness after aging at 450°C for 100 h, while the specimens with larger dislocation density reach to peak hardness faster from the Vickers hardness test result. The result of transmission electron microscopy (TEM) indicates that pre-deformation promotes the process of precipitation of Cu-rich clusters and inhibits the growth of the Cu-rich clusters.

Fatigue Properties of the Aluminium Alloy AW-5182 in dependence on Deformation

Fatigue properties of the constructional materials belong among the very important material parameters, mainly because they are very closely related with the total fatigue life of the part. Knowledge of the boundary between limited and infinite (endurance) life represents a truly very important fatigue parameter. This paper deals with the influence of pre-deformation on aluminium alloy AW-5182 fatigue properties. These tests were performed under fully reversed harmonic cycle (max/min stress ratio R = -1). As a major aim there was determination of so-called S-N curves (stress vs. number of cycles) and their mathematical description by the Basquin's equation via fatigue strenght coefficient σf' [MPa] and fatigue strength exponent b [1]. Measured S-N curves gave a basic overview about the basic pre-deformation influence on the alluminium alloy AW-5182 fatigue properties.

Temperature Dependent Plastic Deformation Behavior of AZ31 Magnesium Alloy in Uniaxial and Biaxial Compressions

Metal forming of magnesium alloys often performed at elevated temperature, because magnesium alloys exhibit peculiar stress-strain relation and inferior ductility compared to conventional metals at room temperature. In the present study, deformation behavior and formability of cast and extruded AZ31 magnesium alloys under uniaxial and biaxial compressions at room temperature and at elevated temperatures were investigated. The results revealed that the compressive stress-strain relation of AZ31 magnesium alloy changed not only with the initial texture but also with the deformation temperature. The temperature dependency of flow stress of the cast alloy was smaller than that of the extruded alloy probably because of less influence of pre-deformation. In addition, the influence of compressive deformation pattern upon flow stress of the extruded alloy remained even at elevated temperature to 523 K. The temperature dependency of compressive fracture was also discussed and it was found that the equi-biaxial condition improved the compressive formability at elevated temperatures.

Influence of Pre-deformation on Aging Precipitation Behavior of Three Al–Cu–Li Alloys

The influence of pre-deformation on aging precipitates of three near peak-aged Al–Cu–Li alloys, 1460 alloy with a low Cu/Li ratio (1.46), 2050 alloy with a high Cu/Li ratio (4.51) and 2A96 alloy with a medium Cu/Li ratio (2.97), was investigated. The strength of the aged alloys is enhanced by the pre-deformation. The effectiveness of pre-deformation on precipitates is dependent on the alloy’s composition. With increasing the pre-deformation, the population density of T1 (Al2CuLi) precipitates increases in all three Al–Cu–Li alloys and their diameter decreases in 2050 and 2A96 alloys, and the greatest effectiveness is observed in 2A96 alloy. The pre-deformation also increases the population density of θ′ (Al2Cu) precipitates and decreases their diameter in 2050 and 2A96 Al–Li alloys, but the effectiveness is smaller compared to that on T1 precipitates. In 1460 alloy subjected to two-step aging at 130 °C for 20 h followed by 160 °C for 12 h, the main precipitates are δ′ (Al3Li). At 2%–6% pre-deformation, GP-I zones form and pre-deformation displays little influence. Eight percentage pre-deformation promotes θ″/θ′ precipitation and increases their population density.

Influence of pre-deformation, sensitization and oxidation in high temperature water on corrosion resistance of AISI 304 stainless steel

The effects of pre-deformation on sensitization of AISI 304 stainless steel were investigated by the double loop electrochemical potentiokinetic reactivation test. The effects of pre-deformation and sensitization on high temperature oxidized film formed in high temperature water were analyzed by a XRD and SEM. The electrochemical impedance spectroscopy at room temperature was used to study corrosion resistance of oxidized film. The point defect density of oxidized film was calculated by Mott–Schottky plots. The results showed that the value of the degree of sensitization first decreased and then slight increased with the increasing of engineering strain. Moreover, low temperature promoted to form sensitization induced “secondary” α′-martensite. The sample with 20% engineering strain had higher impedance value than other samples. The result was supported by further Mott–Schottky experiments. Considering increased α′-martensite with the increasing of strain, the results of the impedance were more consistent with values of the degree of sensitization.

Influence of pre-deformation and subsequent ageing on the hardening behavior and microstructure of 2219 aluminum alloy forgings

Applying pre-deformation to high strength aluminum alloy between solution treatment and artificial ageing is an effective way to improve the mechanical properties. The influence of the pre-deformation and subsequent ageing on the hardening behavior and microstructure of 2219 aluminum alloy forgings have been analyzed through TEM, Vickers hardness and mechanical property tests. The results show that the mechanical properties of pre-deformed forgings are better than those of non-deformed ones and are more evenly distributed. Furthermore, the ageing precipitation is enhanced, the ageing time is shortened, and the hardness and the strength are increased. As compared with non-deformed forgings, the forgings with 3% pre-deformation ageing treatment (DAT) have higher tensile strength by 11.9%, higher yield strength by 26.2% and much lower in forgings anisotropy (IFA). These differences are attributed to the combined effects of heterogeneous nucleation and growth of precipitates at dislocations in the pre-deformed forgings. Through TEM, it is found that precipitates are more dispersive. Thus, it can be concluded that obviously, the pre-deformation ageing treatment can optimize the microstructure and the mechanical properties of 2219 aluminum alloy forgings.

Nonlinear vibration of rotating pre-deformed blade with thermal gradient

In this paper, the nonlinear dynamic behavior is investigated for a rotating pre-deformed pre-twisted blade subjected to harmonic gas pressure. The pre-deformation curve produced by thermal gradient is derived. A novel nonlinear vibration system is established by considering the influence of pre-deformation. The combination of the Lagrange principle and the assumed modes method is utilized to obtain the motion equations, and then the equations are transformed into a dimensionless form through introducing a set of dimensionless parameters. For the purpose of ensuring high precision in determination of the internal resonance condition, the equations of motion are discretized by adequate trial functions. An eigenvalue analysis is conducted on the corresponding linear system to obtain the natural frequencies and examine the possibility of the 2:1 internal resonance. The method of multiple scales is developed to solve the resulting multi-degree-of-freedom nonlinear ordinary differential equations. A numerical integration by means of Runge–Kutta is performed to establish the validity of the derived formulations. The evolution of frequency response curves with the rotating speed is observed. The influences of the thermal gradient, gas pressure and damping coefficient on the resonant dynamics of the system are investigated in detail. For the purpose of comparison, another distribution profile of pre-deformation, which is frequently used in previous literature, is also examined. It could be found that not only the amplitude but also the distribution of the initial deflection could influence the steady-state nonlinear response of the pre-deformed blade. A series of interesting nonlinear dynamic phenomena are discovered from the results.

Influence of predeformation on microstructure evolution of superplastically formed Al 5083 alloy

Cavitation is the main defect encountered during superplastic forming (SPF) of thin sheet aluminum alloys. In the present paper, the influence of preforming operation (cold or hot) on the superplastic forming ability and quality of 1.6-mm-thick sheet of 5083 SPF aluminum alloy is investigated. Specifically, grain size evolution and the characteristics of the cavitation process are discussed as a function of prior deformation and the preforming temperature. Optical and field emission gun scanning electron microscopy (FEG-SEM) were used to study the characteristics of the cavities and microstructure evolution. Image processing was used to measure the surface and volume fractions of the cavities. The results indicate that hot preforming leads to a lower number of cavities per unit surface compared to cold preforming prior to the SPF operation. However, the average cavity sizes and the average grain size are higher in the case of hot preforming compared to cold preforming, which lead to higher susceptibility to crack formation and reduced SPF ability of the alloy.

Strength improvement in ZK60 magnesium alloy induced by pre-deformation and heat treatment

The influence of pre-deformation and heat treatment on mechanical properties of as-extruded ZK60 alloy was investigated. The experimental results indicated that the solid solution, pre-cold rolling and artificial aging treatments remarkably improved the mechanical strength of alloys compared with the as-extruded condition. Especially, pre-cold rolling in 5% reduction combined with artificial aging at 150 °C for 20 h was determined as the optimum heat treatment condition, which resulted in a yield strength of 333 MPa with an increment of 87 MPa and ultimate tensile strength of 373 MPa. High density of nanoscale precipitates in α-Mg matrix observed in this sample was beneficial to enhancing the strength. The as-extruded sample showed a typical brittle fracture while the solution treated sample exhibited ductile-fragile failure characterized by cleavage fractures, river patterns, and tear ridges. And the sample after pre-cold rolling combined with aging presented more equiaxial dimples with a great amount of cracked particles in them. The above-mentioned observations were analyzed in terms of microstructure and possible strengthening mechanism in the extruded ZK60 alloy.

Influence of fiber orientation on the ballistic performance of needlepunched nonwoven fabrics

The influence of the initial fiber orientation distribution on the ballistic performance of a needlepunched nonwoven polyethylene fabric was analyzed. To this end, ballistic tests were carried out in specimens pre-deformed along the machine or the transverse directions and the influence of pre-deformation on the fiber orientation was measured by means of wide angle X-ray diffraction. It was found that pre-deformation along the machine direction (the soft orientation of the fabric) led to more isotropic in-plane mechanical response and to a marked increase in the specific ballistic limit and in the energy dissipated by unit weight while the opposite behavior was found after stretching the fabric along the transverse direction. These differences were accompanied by changes in the penetration mechanics from extensive fiber pull-out to slippage between fibers in the network. These results highlight how the nature of the nonwoven microstructure (connectivity of the entanglement points and fiber orientation distribution) can be tailored to improve the impact performance.