Research on flow stress of spray formed 70Si30Al alloy under hot compression deformation

The flow stress of spray formed 70Si30Al alloy was studied by hot compression on a Gleeble-1500 test machine. The experimental results indicated that the flow stress depends on the strain rate and the deformation temperature. The flow stress increases with an increase in strain rate at a given deformation temperature. The flow stress decreases with the defor- mation temperature increasing at a given strain rate. The relational expression among the flow stress, the strain rate, and the deformation temperature satisfies the Arrhenius equation. The deformation activation energy of 70Si30Al alloy during hot deformation is 866.27 kJ/mol from the Arrhenius equation.

Flow stress behavior of Al-Cu-Li-Zr alloy containing Sc during hot compression deformation

The flow stress behavior of Al-3.5Cu-1.5Li-0.25(Sc+Zr) alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa-1 and 1.51×1016 s-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.

Flow stress equation for multipass hot-rolling of aluminum alloys

A series of simple axisymmetric compression tests were carried out on the computer servo controlled Gleeble 1 500 machine when strain rates ranged between 0.05 25 s -1 and deformation temperature 300 500 ℃. The results show that flow stress is related to the Zener Hollonom parameter Z and strain, as well as the static recrystallization fraction between passes during multipass hot deformation of 5182 aluminum alloy. Hence, a modified exponential flow stress equation was presented by considering the values of ln A and β as functions of strain, and by using the uniform softening method and incorporating the static recrystallization fraction between passes to consider the effects of residual strain during multipass hot rolling of 5182 aluminum alloy. The validity of the equation was examined by a typical non isothermal multipass deformation test.

Flow stress of 2197 Al-Li alloy during hot compression deformation

The flow stress behavior of 2197 Al-Li alloy during hot compression deformation was studied in the strain rate range from 0.01 to 10 s-1 and the temperature range from 360 to 510 ℃ by isothermal compression test on a Gleeble-1500 thermal-mechanical simulator. The results show that the flow stress of 2197 Al-Li alloy decreases with the increase of deformation temperature and increases with the increase of strain rate. The peak flow stress during high temperature deformation can be represented by Z parameter in a hyperbolic sine function. The analytical expression of peak flow stress was fitted with the hot deformation activation energy of 260.6 kJ/mol.

Effects of hot deformation parameters on flow stress and establishment of constitutive relationship system of BT20 titanium alloy

The hot compression experiments were performed to investigate the effects of hot deformation parameters on the flow stress of BT20(Ti-6Al-2Zr-1Mo-1V) titanium alloy. The results show that the flow stress decreases with the increment of deformation temperature and increases with the growth of strain rate. The peak stress moves toward the direction of strain reducing and the strain rate sensitivity increases with the rising deformation temperature. There is obvious deformation heating created during hot deformation under relatively higher strain rate and lower deformation temperature. The improved back propagation(BP) neural network with 3-20-16-1 architecture has been employed to establish the prediction model of flow stress using deformation degree, deformation temperature and strain rate as input variables. The predicted values obtained by BP network agree well with the measured values, the relative error is within 6.5% for the sample data and not bigger than 9% for the non-sample data, which indicates that the ANNs adopted can predict the flow stress of BT20 alloy effectively and can be used as constitutive relationship system applied to FEM simulation of plastic deformation.

Feature of flow stress of aluminum sheet used for can during hot compression

The flow stress feature of aluminum sheet used for pressure can during plastic deformation at elevated temperature was studied by isothermal compression test using Gleeble 1 500 dynamic materials testing machine. The experimental results show that the steady state deformation is remarkable when the material is deformed in the temperature range of 350～500 ℃ at strain rates within the range of 10 -2 ～10.0 s -1 . The material is sensitive to positive strain rate. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate, and an Arrhenius relationship with the temperature. Semi empirical constitutive equations of the flow stress are derived from all experimental data for tested material during plastic deformation at elevated temperature by polyelement linear regression analysis. [

Dynamic Recrystallization Behavior of 7056 Aluminum Alloys during Hot Deformation

To investigate the dynamic recrystallization behavior of 7xxx aluminum alloys,the isothermal compression tests were carried on the 7056 aluminum alloy in the temperatures range of 320-440℃and in the strain rates range of 0.001-1 s^(-1).In addition,the microstructure of samples were observed via electron back scanning diffraction microscope.According to the results,true stress and true strain curves were established and an Arrhenius-type equation was established,showing the flow stress increases with the temperature decreasing and the strain rate increasing.The critical strain(ε_(c))and the critical stress(σ_(c))of the onset of dynamic recrystallization were identified via the strain hardening rate and constructed relationship between deformation parameters as follows:ε_(c)=6.71×10^(-4)Z^(0.1373) and σ_(p)=1.202σ_(c)+12.691.The DRX is incomplete in this alloy,whose volume fraction is only 20%even if the strain reaches 0.9.Through this study,the flow stress behavior and DRX behavior of 7056 aluminum alloys are deeply understood,which gives benefit to control the hot working process.

A FLOW STRESS MODEL FOR AZ61 MAGNESIUM ALLOY

The flow stress behaviors of AZ61 alloy has been investigated at temperature range from 523 to 673K with the strain rates of 0.001-1s-1.It is found that the average activation energy,strain rate sensitive exponent and stress exponent are different at various deformation conditions changing from 1i3.6 to 176.3k J/mol,0.125 to 0.167 and 6 to 8 respectively.A flow stress model for AZ61 alloy is derived by analyzing the stress data based on hot compression test.It is demonstrated that the flow stress model including strain hardening exponent and strain softening exponent is suitable to predicate the flow stress.The prediction of the flow stress of AZ61 alloy has shown to be good agreement with the test data.The maximum differences of the peak stresses calculated by the model and obtained by experiment is less than 8%.

Microstructure and Flow Stress of Mg-12Gd-3Y-0.5Zr Magnesium Alloy

The microstructure and flow stress of the Mg-12Gd-3Y-0.5Zr magnesium alloy was investigated by compression test at temperatures ranging from 350 to 500 ℃ and the strain rates ranging from 0.01 to 20 s-1. The flow stress of the magnesium alloy increased with strain rate and decreased with deformation temperature. Flow stress can be expressed in terms of the Zener-Hollomon parameter Z, which describes the combined influence of the strain rate and temperature using an Arrhenius function.The values of the deformation activation energy were estimated to be 245.9 and 171.5 kJ/mol at deformation temperatures below 400 ℃ and above 400 ℃, respectively. Two constitutive equations were developed to quantify the effect of the deformation conditions on the flow stress of the magnesium alloy. The effects of deformation temperature and strain rate on the microstructure of the magnesium alloy were also examined and quantified by measuring the volume fraction of dynamically recrystallized grain Xd. Xd increased with increasing of deformation temperature. When the deformation temperature was below 475 ℃, Xd decreased with strain rate until it reached 0.15 s-1, then it increased again. When the deformation temperature was above 475 ℃, Xd increased with strain rate.

Flow behavior and microstructure evolution of TB8 alloy during hot deformation process

Hot compression tests of metastable β titanium alloy TB8 were carried out using a Gleeble-1500 thermal simulation testing machine in the temperature range of 750-1100 ℃, at constant strain rate from 0.01 s-1 to 1 s-1 and with height direction reduction of 60%. Flow stress behavior and microstructure evolution during hot compression of TB8 alloy were investigated. The hyperbolic-sine-type constitutive model of TB8 alloy was obtained to provide basic data for determining reasonable forming process. The results indicate that hot deformation behavior of TB8 alloy is highly sensitive to the temperature and strain rate. An analysis of the flow stress dependence on strain rate and temperature gives a stress exponent of n≈3.416 19 and a deformation activation energy of Q≈227.074 4 kJ/mol. According to the deformation microstructure, no dynamic recrystallization happens below β-phase transus temperature and as a result dynamic recovery is the predominant softening mechanism. On the other hand, the main softening mechanism is characterized as dynamic recrystallization at a slow strain rate above β-phase transus temperature.

Hot deformation behavior of KFC copper alloy during compression at elevated temperatures

The hot deformation behavior of a KFC copper alloy was studied by compression deformation tests on Gleeble 1500 machine at strain rates ranging between 0.01?10 s?1 and deformation temperature of 650?850 ℃, and associated structural changes were studied by observations of metallography and TEM. The results show that the true stress–true strain curves for a KFC copper alloy are characterized by multiple peaks or a single peak flow, and tend to a steady state at high strains. The peak stress can be represented by a Zener-Hollomon parameter in the hyperbolic-sine-type equation with the hot deformation activation energy Q of 289 kJ/mol. The dynamic recrystallization(DRX) occurs by bulging out of part serrated grain-boundary, and the dynamic recrystallization grain size is dependent sensitively on deformation temperature T and strain rate ε&, also a function of Z. The dynamic spherical Fe-rich precipitates and successive dynamic particles coarsening has been assumed to be responsible for flow softening at high strains, and this is more effective when samples deformed at low temperatures and higher strain rates.

Hot compression deformation behavior of MB26 magnesium alloy

The flow stress features of MB26 magnesium alloy were studied by isothermal compression at 300-450 ℃ and strain rate of 0.001-1 s-1 with Gleeble 1500 thermal simulator. In addition,the deformation activation energy Q was calculated. The results show that the strain rate and deformation temperature have obvious effect on the true stress. The peak value of flow stress becomes larger with increasing strain rate at the same temperature,and gets smaller with the increasing deformation temperature at the same strain rate. The alloy shows partial dynamic recrystallization. The flow stress of MB26 magnesium alloy during high temperature deformation can be represented by Zener-Hollomon parameter including the Arrhemius term. The temperature range of 350-400 ℃ is suggested for hot-forming of this alloy.

A new flow stress model based on Arrhenius equation to track hardening and softening behaviors of Ti6Al4V alloy

The conventional Arrhenius-type model was adopted to identify the deformation characteristic of Ti6 A14 V(TC4) titanium alloy based on the stress-strain curves of isothermal compression test. A new flow stress model based on Arrhenius equation was proposed for TC4,which is composed of peak flow stress(PFS) prediction and strain compensation. The predicted PFS is set as a reference to derive the flow stress model at any strain ranging from approximately 0 to 0.7. The predictability and efficiency among the proposed model, conventional model,and an existing physical-based model of TC4 were comparatively evaluated. It is found that the newly proposed model can simultaneously track the hardening and softening behaviors of TC4 through a single expression while the other existing models are only valid in the softening region.Besides, the wider application range and acceptable accuracy of the new model have been achieved by fewer material constants with much-simplified modeling procedure than the other models.

Deformation behavior and microstructure of an Al-Zn-Mg-Cu-Zr alloy during hot deformation

The hot deformation behavior and microstructures of Al-7055 commercial alloy were investigated by axisymmetric hot compression at temperatures ranging from 300°C to 450°C and strain rates from 10-2 to 10 s-1,respectively.Microstructures of deformed 7055 alloy were investigated by transmission electron microscopy (TEM).The dependence of peak stress on deformation temperature and strain rate can be expressed by the hyperbolic-sine type equation.The hot deformation activation energy of the alloy is 146 kJ/mol.Moreover,the flow stress curves predicted by the modified constitutive equations are reasonably consistent with the experimental results,which confirms that the proposed deformation constitutive equations can provide evidence for the selection of hot forming parameters.TEM results indicate that dynamic recovery is the main softening mechanism during hot deformation.

Flow stress behavior of high-purity Al-Cu-Mg alloy and microstructure evolution

The flow stress behavior of high-purity Al-Cu-Mg alloy under hot deformation conditions was studied by Gleeble-1500,with the deformation temperature range from 300 to 500 °C and the strain rate range from 0.01 to 10 s-1. From the true stress-true strain curve, the flow stress increases with the increasing of strain and tends to be constant after a peak value, showing dynamic recover, and the peak value of flow stress increases with the decreasing of deformation temperature and the increasing of strain rate.When the strain rate is 10 s-1 and the deformation temperature is higher than 400 °C, the flow stress shows dynamic recrystallization characteristic. TEM micrographs were used to reveal the evolution of microstructures. According to the processing map at true strain of 0.7, the feasible deformation conditions are high strain rate(>0.5 s-1) or 440-500 °C and 0.01-0.02 s-1.

Effect of squeeze casting process on microstructures and flow stress behavior of Al-17.5Si-4Cu-0.5Mg alloy

The effects of squeeze casting process on microstructure and flow stress behavior of Al-17.5Si-4Cu-0.5Mg alloy were investigated and the hot-compression tests of gravity casting and squeeze casting alloy were carried out at 350-500°C and 0.001-5s-1.The results show that microstructures of Al-17.5Si-4Cu-0.5Mg alloys were obviously improved by squeeze casting.Due to the decrease of coarse primary Si particles,softα-Al dendrite as well as the fine microstructures appeared,and the mechanical properties of squeeze casting alloys were improved.However,when the strain rate rises or the deformation temperature decreases,the flow stress increases and it was proved that the alloy is a positive strain rate sensitive material.It was deduced that compared with the gravity casting alloy,squeeze casting alloy(solidified at 632 MPa)is more difficult to deform since the flow stress of squeeze casting alloy is higher than that of gravity casting alloy when the deformation temperature exceeds 400°C.Flow stress behavior of Al-17.5Si-4Cu-0.5Mg alloy can be described by a hyperbolic sine form with Zener-Hollomon parameter,and the average hot deformation activation energy Q of gravity casting alloy and squeeze casting alloy is 278.97 and 308.77kJ/mol,respectively.

Hot compressive deformation behavior and constitutive relationship of Al-Zn-Mg-Zr alloy with trace amounts of Sc

The hot deformation behaviors of Al-Zn-Mg-Sc-Zr alloy were investigated in a temperature range of 340 500°C and a strain rate range of 0.001 10 s 1using uniaxial compression test on Gleeble-1500 thermal simulation machine.The results show that the flow stress increases with increasing strain and tends to be constant after a peak value.The flow stress increases with increasing strain rate and decreases with increasing deformation temperature.The phenomenon of dynamic recovery and dynamic recrystallization can be observed by microstructural evolutions.Based on the hyperbolic Arrhenius-type equation,the true stress true strain data from the tests were employed to establish the constitutive equation considering the effect of the true strain on material constants(,β,Q,n and A),which reveals the dependence of the flow stress on strain,strain rate and deformation temperature.The predicted stress strain curves are in good agreement with experimental results,which confirms that the developed constitutive equations are suitable to research the hot deformation behaviors of Al-Zn-Mg-Sc-Zr alloy.

Hot-compression constitutive relation of as-cast AZ31 magnesium alloy

In hot-compression process,the various factors have obvious effects on the deformation behavior of AZ31 magnesium alloy deformation behavior. To understand the hot-compression constitutive relation thoroughly,the stress-strain behavior of AZ31 magnesium alloy at various strain rates and different deformation temperatures were investigated under maximum strain of 60%. The microstructure of the experimental alloy was studied in the hot-compression procedure. The experimental results show that the relation of peak flow stress,strain rate and temperature can be described by Z parameter which contains Arrheniues item. The strain rate and the deformation temperature are the key parameters affecting deformation activation energy.

Dynamic modeling of twin roll casting AZ41 magnesium alloy during hot compression processing

A dynamic material model of Mg-4.51Al-1.19Zn-0.5Mn-0.5Ca(AZ41,mass fraction,%)magnesium alloy was put forward.The results show that the dynamic material model can characterize the deformation behavior and microstructure evolution and describe the relations among flow stress,strain,strain rates and deformation temperatures.Statistical analysis shows the validity of the proposed model.The model predicts that lower deformation temperature and higher strain rate cause the sharp strain hardening. Meanwhile,the flow stress curve turns into a steady state at high temperature and lower strain rate.The moderate temperature of 350 ℃and strain rate of 0.01 s-1 are appropriate to this alloy.