Effect of pre-deformation on the stress corrosion cracking susceptibility of aluminum alloy 2519

The effects of pre-deformation and strain rate on the stress corrosion cracking （SCC） behavior of aluminum alloy 2519 in air and in 3.5% NaCI water solution were investigated by means of slow strain rate tension （SSRT）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results indicate that the alloy is susceptible to SCC in 3.5% NaCI water solution and not in air. At the same pre-deformation, the alloy is more susceptible to SCC at 1.33 × 10^-5 s^-1 than at 6.66 × 10^-5 s^-1. Moreover, it is more susceptible to SCC at free pre-deformation than at 10% pre-deformation at the same strain rate. The number of 0 precipitated along the grain boundaries is reduced and distributed discontinuously, at the same time, the precipitate-free zones （PFZ） become narrow and the susceptibility to stress corrosion cracking is reduced after 10% pre-deformation.

Effect of pre-deformation on microstructure and mechanical properties of WE43 magnesium alloy II: Aging at 250 and 300℃

In this work,the microstructural evolution and mechanical properties of a pre-deformed WE43 magnesium alloy when aged at 250 and 300℃ were further investigated.It is found that the abundant deformation twins introduced by pre-deformation were maintained within the alloy during the aging treatment.Second particles formed at the twin boundaries and coarsened with aging time,especially at 300℃.When peak-aged at 250℃,the fine metastable β'''and β' precipitates formed in the un-deformed alloy have been transformed into relatively large β1 and β precipitates by the pre-deformation.While peak-aged at 300℃,the pre-deformation obviously refined the β precipitates.Mechanical properties indicate that pre-deformation can increase the yield strength by 19MPa and 54MPa for the peak-aged alloy at 250℃ and 300℃,respectively,and will not obviously deteriorate the tensile elongations.

Pre-deformation for Assembly Performance of Machine Centers

The current research of machine center accuracy in workspace mainly focuses on the poor geometric error subjected to thermal and gravity load while in operation, however, there are little researches focusing on the effect of machine center elastic deformations on workspace volume. Therefore, a method called pre-deformation for assembly performance is presented. This method is technically based on the characteristics of machine tool assembly and collaborative computer-aided engineering （CAE） analysis. The research goal is to enhance assembly performance, including straightness, positioning, and angular errors, to realize the precision of the machine tool design. A vertical machine center is taken as an example to illustrate the proposed method. The concept of travel error is defined to obtain the law of the guide surface. The machine center assembly performance is analyzed under cold condition and thermal balance condition to establish the function of pre-deformation. Then, the guide surface in normal direction is processed with the pre-deformation function, and the machine tool assembly performance is measured using a laser interferometer. The measuring results show that the straightness deviation of the Z component in the Y-direction is 158.9% of the allowable value primarily because of the gravity of the spindle head, and the straightness of the X and Y components is minimal. When the machine tool is processed in pre-deformation, the straightness of the Z axis moving component is reduced to 91.2%. This research proposes a pre-deformation machine center assembly method which has sufficient capacity to improving assembly accuracy of machine centers.

Effects of pre-deformation on microstructure and properties of Al–Cu–Mg–Ag heat-resistant alloy

The effects of the pre-deformation on the microstructure, mechanical properties and corrosion resistance of Al–Cu–Mg–Ag alloys were investigated by means of hardness tests, tensile tests, intergranullar corrosion(IGC) tests and transmission electron microscopy(TEM), respectively. The results show that with the increase of deformation amount, the aging hardening rate increases while the strength of the alloy decreases and then increases. The sample with a pre-deformation of 6% possesses the highest tensile strength due to the refinedly and homogeneously distributed precipitations. The pre-deformation aging accelerates the heterogeneous nucleation of ? and θ′ phases at dislocations, and also refines the precipitations both in the grains and along the grain boundaries. The precipitation of ? phase is restrained while that of θ′ phase is accelerated in pre-deformed Al–Cu–Mg–Ag alloy compared with the sample without pre-deformation. In addition, the width of the precipitate free zone decreases with increasing the pre-deformation amount, leading to a narrower IGC passageway. This results in an enhanced IGC resistance of Al–Cu–Mg–Ag alloy treated by pre-deformation aging.

Variation of the uniaxial tensile behavior of ultrafine-grained pure aluminum after cyclic pre-deformation

To explore the influence of cyclic pre-deformation on the mechanical behavior of ultrafine-grained（UFG）materials with a high stacking fault energy（SFE）,UFG Al processed by equal-channel angular pressing（ECAP）was selected as a target material and its tensile behavior at different pre-cyclic levels D（D=N_i/N_f,where N_i and N_f are the applied cycles and fatigue life at a constant stress amplitude of 50 MPa,respectively）along with the corresponding microstructures and deformation features were systematically studied.The cyclic pre-deformation treatment on the ECAPed UFG Al led to a decrease in flow stress,and a stress quasi-plateau stage was observed after yielding for all of the different-state UFG Al samples.The yield strengths_（YS）,ultimate tensile strengths_（UTS）,and uniform straineexhibited a strong dependence on D when D≤20%;however,when D was in the range from 20%to 50%,no obvious change in mechanical properties was observed.The micro-mechanism for the effect of cyclic pre-deformation on the tensile properties of the ECAPed UFG Al was revealed and compared with that of ECAPed UFG Cu through the observations of deformation features and microstructures.

Effect of Pre-Deformation Enhanced Thermal Aging on Precipitation and Microhardness of a Reactor Pressure Vessel Steel

Microstructure evolution in neutron irradiated Reactor Pressure Vessel （RPV） steels was experimentally simulated through an improved degradation procedure in this study. The degradation procedure includes austenitizing at 1 150℃ and water quench, deformation 10% and 30% respectively, and then thermal aging at 500℃ for different period of time. The microstructure of the specimens was analyzed in details using transmission electron microscopy （TEM）. The micro-hardness test results showed that all the hardness curves of undeformed, 10% pre-deformed and 30% pre-deformed specimens have two micro-hardness peaks with the first peak value corresponding to different thermal aging time of 1 hour, 5 hours and 10 hours, respectively. It was revealed that the hardness curves were influenced by the precipitation of Cu-rich precipitates （CRPs） and carbides, deposition of martensite and work hardening.

Effect of Austenite Pre-deformation on Isothermal Martensite Transformation in an Fe-20.5Ni-4.8Mn Alloy

With electron microscopy the investigation on isothermal martensite transformation in an Fe20.5Ni-4.8Mn alloy has been carried out to clarify the effect of austenite state on the transformation, by applying pre-deformation to austenite before isothermal holding. Under the condition without pre-deformation, the isothermal martensite products are lath martensite with {111}fhabit planes. Dislocations in austenite seem to contribute to nucleation of martensite, and in this nascent Stage austenite substructure has no obvious effect on martensite growth. The consequent thickening of martensite laths is apparently influenced by local austenite states, resulting in the changes in orientation, morphology as well as substructure of martensite lath. The kinetics of isothermal martensite transformation is controlled by intedece dislocation determined nucleation of martensite in primary stage, but to a larger extent, by the austenite accommodation for the shape strain of martensite in the thickening Stage

Effect of Pre-deformation on Abnormal Segregation of Grain Boundary during Recrystallization Process

The softening rates of Fe-30%Ni alloy containing boron after 10% and 40% deformation at 1000℃ have been measured by a method of interrupted compression, the recrystallization process has also been evaluated.The moving velocity of the boundary of new recrystallizing grain which was growing into the deformed grans has been calculated semi-quantitatively. By means of PTA technique, the abnormal segregation phenomenon on the moving boundary during recrystallization and the influence of pre-deformation have been investigated and the amount of B segregation on moving grain boundaries has been measured .Results indicate that the abnormal segregation of boundaries, when the new grains are growing, is concemed with the pre-deformation and the moving velocity of the bourdaries. This phenomenon is discussed by the gtain boundary widening mechanism.

Effects of pre-deformation on the martensitic transformation and magnetocaloric property in Ni-Mn-Co-Sn ribbons

This paper investigates the martensitic transformation and magnetocaloric effect in pre-deformed Ni-Mn-Co Sn ribbons. The experimental results show that the reverse martensitic transformation temperature TM increases with the increasing pre-pressure, suggesting that pre-deformation is another effective way to adjust TM in ferromagnetic shape memory alloys. Large magnetic entropy changes and refrigerant capacities are obtained in these ribbons as well. It also discusses the origin of the enhanced martensitic transformation temperature and magnetocaloric property in pre-deformed Ni-Mn Co-Sn ribbons.

Combined Effects of Pre-deformation and Preaging on the Mechanical Properties of Al-Cu-Mg Alloy with Sc and Zr Addition

The combined effects of pre-deformation and pre-aging on the mechanical properties of AlCu-Mg alloy with Sc and Zr addition were investigated. It is revealed that the introduction of pre-deformation can enhance the peak-aging strength, as well as tensile and yield strength, effectively due to the formation of finer and more dispersive precipitation. Pre-aging process before pre-deformation can increase the elongation while maintaining higher strength with a discontinuous distribution of precipitates at grain boundary. The precipitates of bean-like Al3（Sc, Zr） particles further strengthen the alloy via pinning the dislocations which are formed during pre-deformation process and hindering the dislocation motion. Furthermore, pre-deformation and pre-aging accelerate the kinetics of precipitation due to preferential sites provided by the dislocation and the increase of GPB zones＇ size and distribution. The synergism of pre-deformation and pre-aging achieves a combination of better mechanical properties and shorter peak-aging time.

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（Al2Cu Li） 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 ℃ for 20 h followed by 160 ℃ 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.

Obtaining Ultra-High Strength and Ductility in a Mg–Gd–Er–Zn–Zr Alloy via Extrusion,Pre-deformation and Two-Stage Aging

The Mg–12Gd–1Er–1Zn–0.9 Zr(wt%)alloy with ultra-high strength and ductility was developed via hot extrusion combined with pre-deformation and two-stage aging treatment.The age-hardening behavior and microstructure evolution were investigated.Pre-deformation introduced a large number of dislocations,resulting in strain hardening and higher precipitation strengthening in the subsequent two-stage aging.As a result,the alloy showed a superior strength–ductility balance with a yield strength of 506 MPa,an ultimate tensile strength of 549 MPa and an elongation of 8.2%at room temperature.The finer and denserβ’precipitates significantly enhanced the strength,and the bimodal structure,smallβ-Mg5RE phase as well as denseγ’precipitates ensured the good ductility of the alloy.It is suggested that the combination of pre-deformation and two-stage aging treatment is an eff ective method to further improve the mechanical properties of wrought Mg alloys.

The Effect of Pre-Deformation at Elevated Temperatures on the Microstructure and Hardness of Boron Steel 22MnB5

To investigate the effects of the pre-deformation and deformation temperature on the microstructure and hardness of boron steel 22MnB5,isothermal tensile tests were carried out on the Gleeble 3800 system when the temperatures are 700℃,750℃,800℃,respectively.Three specimens were employed to obtain different deformation levels at each temperature.The cooling rate before and after deformation was 30℃/s.Then the microstructures of the specimens were observed and the harness of each specimen was measured.The results show the martensitic fraction decreases and the ferrite fraction increases with decreasing the deformation temperature or increasing the deformation level.The specimens deformed at higher temperature have greater hardness.The hot plastic deformation of austenite shortens the incubation period of ferrite transformation and accelerates the transformation rate.In addition,the isothermally holding time is longer in the case of a larger deformation amount,more austenite will transform to ferrite.Especially,the specimen deformed at 700℃ and with large deformation has almost full massive ferrite microstructure with larger size.

Revisiting the Hierarchical Microstructures of an Al-Zn-Mg Alloy Fabricated by Pre-deformation and Aging

Pre-deformation before aging has been demonstrated to have a positive effect on the mechanical strength of the 7N01 alloy in our previous study,which is rather different from the general negative effects of pre-deformation on high-strength 7XXX aluminum alloys.In order to explain the strengthening mechanism relating to the positive effect,in the present study,the microstructure of the aged 7N01 alloy with different degrees of pre-deformation was investigated in detail using advanced electron microscopy techniques.Our results show that,without pre-deformation,the aged alloy is strengthened mainly by the η′type of hardening precipitates.In contrast,with pre-deformation,the aged alloy is strengthened by the hierarchical microstructure consisting of the GP-η′type of precipitates formed inside sub-grains,the ηp type of precipitates formed at small-angle boundaries,and the dislocation introduced by pre-deformation(residual work-hardening effect).By visualizing the distribution of theηp precipitates through three-dimensional electron tomography,the 3 D microstructures of dislocation cells are clearly revealed.Proper combinations of ηp precipitates,GP-η′precipitates and residual dislocations in the alloy are responsible for the positive effect of pre-deformation on its mechanical properties.

Improvement in irradiation resistance of FeCu alloy by pre-deformation through introduction of dense point defect sinks

The irradiation resistance of pre-deformed FeCu alloy was studied using a 3 MeV Fe ion irradiation experiment at room temperature in comparison with that of the as-received sample.Nanoindentation and atom probe tomography(APT) were used to characterize the mechanical properties and solute distribution.The stress-strain curve obtained by nanoindentation shows that the yield strength(σ0.2) of the pre-deformed sample is unexpectedly reduced with an increase in the irradiation dose to five displacements per atom(dpa).We suggest that it results both from the decrease in the dislocation density and the suppression of defects during irradiation.APT shows that the nucleation of the Cu cluster is suppressed;however,its growth is promoted in the pre-deformed sample,resulting in the formation of sparse and coarse clusters at 1 dpa irradiation.These coarse Cu clusters were then unexpectedly refined to finer grains with an increase in the irradiation dose to 5 dpa.Theoretically,the improvement in the resistance to irradiation in the pre-deformed sample is attributed to the dense point-defect sinks,that is,the dislocations and grain boundaries introduced by pre-deformation.In addition,the contributions of the dislocations and grain boundaries to the sink strength are estimated for both the as-received and pre-deformed samples.The results indicate that dislocations,rather than grain boundaries,play a major role after deformation.

Influence of Pre-Deformation on Springback Effect of Advanced High Strength Steel

In sheet metal forming process of automotive components,the springback effect is significant,in particular for Advanced High Strength Steels (AHSS),for example the Dual Phase (DP) steel.Most of construction parts of modern vehicles have very complex shapes and therefore multi-step procedures are necessary to form such a part.Steel sheets,which firstly undergo pre-deformation,can show considerable change in mechanical behavior during the forming process.However,at present there are limited sufficient data concerning pre-deformation effect on the springback available.In this work,a study of influences of different pre-strain levels on the springback of steel sheet made of AHSS materials has been carried out.The sheet specimens were firstly pre-stretched on a tensile testing machine and the pre-strain values were calculated based on the engineering strain.Furthermore,the steel sheets prepared parallel,transverse,and 45° to the rolling direction have been investigated.A modified U-shape forming was used to evaluate the degree of springback of the steel sheets under various conditions.In parallel,FE simulation of the U-shape forming was performed.Both isotropic model using stress-strain responses from tensile test of specimens with different directions and anisotropic Hill’s 48 model have been applied.The experimental results are compared with the sheet metal forming FE simulations.The primarily aim is to basically understand the springback mechanism by means of the simple models.And finally,conclusions with regard to the springback modeling will be presented.

Effect of Pre-deformation on Nanoscale Precipitation and Hardness of a Maraging Stainless Steel

The effect of pre-deformation on nanoscale precipitates and hardness of a maraging stainless steel strengthened by the coprecipitation of Ni_(3)Ti,Mo-enriched and Cr-enriched precipitates was systematically studied using electron back scattered diffraction,transmission electron microscopy and atom probe tomography(APT).Hardness measurements showed that the hardness of specimen with a deformation ratio of 90%peaked at HV 718 aged for 24 h,which is higher than that in the undeformed specimen(HV 603)aged for 72 h at 480℃.APT characterization revealed that pre-deformation could shorten the incubation time of the Mo-enriched and Cr-enriched precipitates.At the early-aged stage,pre-deformation increased the stain energy that inhibited the nucleation of Ni_(3)Ti precipitates,but accelerated the rejection of Mo from Ni-Ti clusters.Besides,the strengthening model indicated that strain hardening(43%)makes a larger contribution to the hardness at the early-aged condition,while precipitation hardening(58%)has most contribution to the hardness at the peak-aged conditition.

Effect of drawbead on forming performance of subsequent sheet

In order to research the plastic performance of sheet going through the drawbead and the simple tensile test of sheet, the influence of drawbead structure parameters on sheet performance and the subsequent performance of the sheet were performed to investigate the residual deformation characteristics of the sheet through different drawbead structures, and also the influences of drawbead structures and geometry parameters on pre-deformation and subsequent forming characters of sheet were analyzed. The results show that the pre-deformation decreases with the increase of the round corner radius, the pre-deformation increase with the increase of the height of drawbead, and the subsequent forming characteristics of sheet going through drawbead are remarkably different from undeformed sheet and these differences heavily depend on the pre-deformation. With the increases of pre-deformation, the yield ratio increases, but the subsequent elongation exponential decreases. These means deformability of the sheet is significantly reduced. As the structure of drawbead changes, the mechanical characteristics of material in different cyclic loading conditions also change. For the BUFDE+Z deep drawing steel sheet, the subsequent performance of the sheet is hardened when the pre-deformation is greater than 0.044. For the DC52D+ZF hot-galvanize steel sheet, the subsequent performance of the sheet begins to harden when the pre-deformation is greater than 0.079, and it presents that the pre-deformation is not bigger than 0.052.

CORRELATION BETWEEN MICROSTRUCTURE AND STRESS CORROSION CRACKING SUSCEPTIBILITY OF 2091 ALLOY

The stress corrosion cracking(SCC) susceptibility of an Al-Li-Cu-Mg-Zr alloy(2091), heat-treated under different regime,has been investigated hy means of tensile tests at slow strain rate.The microstructure has been examined with TEM.The deformation characteristic has also been analysed.The stress corrosion resistance of the alloy was revealed to be mainly affected by the covering rate of T_2-phase over grain boundaries and by the average distance between T_2-phase particles. SCC resistance can be obviously improved by predeforming the alloy at room temper- ature to reduce the precipitation of T_2-phase along grain boundaries.

Non-equilibrium segregation of boron on grain boundary in Fe-30%Ni alloy

The moving boundary non-equilibrium segregation duringrecrystallization and the influence of pre-deformation in Fe-30/100Ni alloy at 1000 deg. C was investigated by the PTA(particle trackingautoradiography)technique, optical and electron microscopy. The re-Sults indicated that intensity of boron segregation on movingboundary after different deformation is concerned with thepre-deformation Degree and the moving speed of the boundary. TheTEM(transmission electron microscopy(result showed that thedislocation density Nearby the moving boundary increase obviously.The phenomena are discussed by the widening grain boundary mechanism.