Isothermal precision forging of complex-shape rotating disk of aluminum alloy based on processing map and digitized technology

Isothermal precision forging of complex-shape rotating disk of aluminum alloy based on processing map and digitized technology

Author's Accepted Manuscript Isothermal precision forging of complexshape rotating disk of aluminium alloy based on processing map and digitized tech...

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Author's Accepted Manuscript

Isothermal precision forging of complexshape rotating disk of aluminium alloy based on processing map and digitized technology Yanqiu Zhang, Shuyong Jiang, Yanan Zhao, Debin Shan

www.elsevier.com/locate/msea

PII: DOI: Reference:

S0921-5093(13)00599-6 http://dx.doi.org/10.1016/j.msea.2013.05.059 MSA29957

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Materials Science & Engineering A

Received date: 5 April 2013 Revised date: 18 May 2013 Accepted date: 21 May 2013 Cite this article as: Yanqiu Zhang, Shuyong Jiang, Yanan Zhao, Debin Shan, Isothermal precision forging of complex-shape rotating disk of aluminium alloy based on processing map and digitized technology, Materials Science & Engineering A, http://dx.doi.org/10.1016/j.msea.2013.05.059 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Isothermal precision forging of complex-shape rotating disk of aluminium alloy based on processing map and digitized technology Yanqiu Zhang a, Shuyong Jiang a, *, Yanan Zhao a, Debin Shan b a

Industrial Training Centre, Harbin Engineering University, Harbin, 150001, China;

b

School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150001,

China

*Corresponding author: Shuyong Jiang E-mail: [email protected] Fax: 86-451-82519952; Tel: 86-13936266338 Industrial Training Centre, Harbin Engineering University, Harbin, 150001, China Abstract: Isothermal precision forging of complex-shape aluminium alloy rotating disk of airplane was systematically investigated by means of digitized technology based on CAD (computer-aided design), CAE (computer-aided engineering) and CAM (computer-aided manufacturing). The constitutive equation of 7A09 aluminium alloy under hot compression was established in order to understand the flow behavior of the metal material during isothermal precision forging. 7A09 aluminium alloy frequently exhibits dynamic recovery in the case of low strain rate, while it can also be characterized by dynamic recrystallization in the case of high strain rate. According to dynamic material model, the hot processing map of 7A09 aluminium alloy was obtained to optimize the process parameters which lead to the stable flow of the metal material during isothermal precision forging. Based on the different preforms, finite element method (FEM)

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was used to simulate the metal flow and predict the forming defects during isothermal precision forging of rotating disk. By controlling the metal flow, the high-quality rotating disk forging was manufactured on the basis of the proper preform through digitized technology. The simulated results are in good accordance with the experimental ones. Keywords: Finite element method; Aluminium alloys; Bulk defromation; Constitutive behavior; Processing map 1. Introduction For the purpose of meeting the requirements for light weight in the aerospace field, aluminum alloy forgings are usually designed based on the integral structure with complex shape. Furthermore, they are characterized by high dimension accuracy, good mechanical properties and perfect flow line distribution. In general, the complex-shape aluminum alloy forgings possess the lightening structures, such as high rib, long ear, thin web, thin wall and so on. The lightening structures lead to the rapid dissipation of heat quantity during forging and thus have an adverse influence on the formability of the forgings. In addition, aluminum alloy usually have a narrow forging temperature interval of about 70

. Therefore, too low forging temperature or too long

forging time leads to the rapid drop of the temperature in the forging preform and thus results in the increase in the deformation resistance as well as the decrease in the material plasticity. Consequently, the finished forgings frequently possess some defects, such as coarse grains, cracks, folding, underfilling and so on [1-3]. Isothermal precision forging is an advanced plastic forming process, in which the dies are heated to the approximately same temperature as the forging and the forging temperature is almost constant in the process of forging. As a candidate for producing a net shape or at least a near-net

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shape workpiece, isothermal precision forging has been increasingly used to form light materials such as aluminium, magnesium and titanium alloys with small forging temperature range. As compared to conventional bulk forging, isothermal precision forging has many advantages, such as uniform temperature distribution, low deformation load, high material plasticity, small machining allowance and so on [4-8]. However, the optimization of the process parameters plays an important role in obtaining the high-quality forgings during isothermal precision forging. In general, the digitized technology becomes a candidate for cost reducing and time saving during isothermal precision forging. The digitized technology deals with the integration of CAD (computer-aided design), CAE (computer-aided engineering) and CAM (computer-aided manufacturing). In particular, as an important simulation and prediction instrument, finite element method (FEM) is plays a significant role in the digitized technology [9-13]. In addition, the knowledge for flow behavior and hot workability of metal materials lays the foundations for optimizing the isothermal precision forging process. The constitutive equation is an important approach to understanding the flow behavior of the metal materials during hot working. On the one hand, the constitutive behavior of the metal materials during hot deformation can be used for understanding dynamic recovery and dynamic recrystallization. On the other hand, the constitutive equation can become a material model for finite element simulation. The hot processing map is another important approach to describing the hot workability of the metal materials. At present, the processing maps are mainly based on atomic model and dynamic material model (DMM) [14]. So far, DMM has been increasingly used in the hot working field because of its practical utility. DMM was first put forward on the basis of continuum mechanics of large plastic deformation, physical system modeling and extremum principle of irreversible

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thermodynamics by Prasad et al [15]. The hot processing map can be used for determining the unstable flow zone of the metal materials during hot deformation in order to optimize the process parameters. So far, it has been widely applied to titanium alloy, magnesium alloy, metal matrix composite and so on [16-22]. In the present study, the constitutive equation and the processing map of 7A09 aluminum alloy were established during hot deformation. Furthermore, isothermal precision forging of complex-shape rotating disk of airplane was systematically investigated by means of digitized technology based on CAD, CAE and CAM. 2. Experimental procedures 2.1. Typical forging Rotating disk of aluminium alloy is an important load-bearing part and is located in the principal shaft of lifting system of airplane. The rotating disk has two inner ears and five outer ears, in which four outer ears have the concaves, as shown in Fig. 1 (a) and (b). In addition, the rotating disk forging must meet the distribution of flow line along the profile in order to guarantee the appropriate load-bearing ability, as shown Fig. 1 (c) and (d). 2.2. Material 7A09 aluminum alloy bar was used as the experimental material, which belongs to T6 state and possesses the diameter of 200 mm. The chemical composition of 7A09 aluminum alloy is shown in Table 1.  2.3. Compression test Hot compression test was carried out on the thermal analogue test machine of Gleeble-1500 type. The compression samples with the height of 12 mm and the diameter of 8 mm were derived

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from the 7A09 aluminum alloy bar. The compression samples were covered with the graphitic lubricant before compression test in order to avoid the inhomogeneous plastic deformation due to friction. During compression test, the compression samples were heated to a certain temperature at the heating rate of 1

·s-1 and then were held for 3 min. Then, the compression samples were

compressed by the deformation degree of 60% at the temperatures ranging from 300

to 460

and at the strain rates ranging from 0.01 s-1 to 10 s-1, and subsequently were quenched into the water at room temperature in order to keep the original microstructures of the compressed samples. All the compressed aluminum alloy samples were cut along the longitudinal direction by means of electro-discharge machining (EDM) and then were made into the metallographic specimens. All the metallographic specimens were etched in a solution containing 1.3% HNO3, 0.4% HCl, 0.3% HF and 98% H2O by volume fraction and subsequently were characterized by XJG-05 optical microscope. 3. Digitized design and manufacturing Digitized design and manufacturing of isothermal precision forging of rotating disk mainly deals with establishment of constitutive equation, construction of hot processing map, computer-aided design (CAD), computer-aided engineering (CAE) and computer-aided manufacturing (CAM), and the flow chart corresponding to digitized design and manufacturing is shown in Fig. 2. 3.1. CAD According to three-dimensional (3D) model of the final workpiece, the 3D model of the cold forging of the rotating disk is established by means of CATIA software. Subsequently, based on the 3D model of the cold forging, the 3D model of the hot forging is obtained by increasing the

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corresponding allowance. According to the 3D model of the hot forging, the cavity profile of the upper die and the bottom die can be established by using Boolean operation module of CATIA software. In the end, the 3D model of isothermal precision forging die is obtained, as shown in Fig. 3. 3.2. CAE CAE is mainly based on finite element simulation of isothermal precision forming of the rotating disk forging. According to the constutive model of 7A09 aluminum alloy, finite element simulation can be used for understanding the flow behavior of the metal material and predicting the defects of the forging during isothermal precision forging. As a result, the process parameters can be optimized by means of finite element simulation. In the present study, DEFORM3D commercial finite element code is used to optimize the preform schemes. Fig. 4 shows two preform schemes, in which one scheme is based on ring preform and the other scheme is determined as pentagram preform. 3.3. CAM CAM lays a great emphasis on numerical control programming during machining of isothermal precision forging die. It deals with planning cutter path, establishing cutter location file, modeling cutter locus and generating numerical code. With the help of the computer, CAD and CAM can be integrated in order to implement the data exchange between CAD and CAM. 4. Constitutive behavior 4.1. Compression deformation behavior Fig. 5 indicates the true stress-strain curves of 7A09 aluminum alloy under compression at the strain rates ranging from 0.01 s-1 to 10 s-1 and at the temperatures ranging from 300

6

to 460

.

It can be found from Fig. 5 that 7A09 aluminum alloy is sensitive to the strain rates since the flow stress of 7A09 aluminum alloy increases with the increase in the strain rate in the case of the same deformation temperature. Furthermore, at the strain rate of 0.01 s-1, the stress-strain curves exhibit a characteristic of steady flow at the temperatures above 400 work hardening at the temperatures of 300

and 350

, while they are characterized by

. However, in the case of the strain rate of

0.1 s-1, the stress-strain curves also possess a feature of steady flow at the temperature of 350

.

With the increase in the strain rate, in the case of the strain rate of 1 s-1, the stress-strain curves are characterized by steady flow even at the temperature of 300

. It is very interesting that when the

strain rate increases to 10 s-1, the stress-strain curves fluctuate sharply before they exhibit the steady flow. It is evident that there is a competition between work hardening and dynamic softening during hot deformation of 7A09 aluminum alloy. In general, work hardening results from the accumulation of the dislocations due to plastic deformation, while dynamic softening is attributed to the decrease in the dislocation density due to dynamic recovery or dynamic recrystallization [23]. It can be generally accepted that the softening mechanism of dynamic recovery results from climb of edge dislocations, cross-slip of screw dislocations and counteraction of unlike dislocations. However, the softening mechanism of dynamic recrystallization is attributed to the annihilation of the dislocations due to nucleation and growth of new recrystallized grains. The balance between working hardening and dynamic softening results in the steady flow of 7A09 aluminum alloy during hot deformation. In general, dynamic recovery occurs at the low strain rates, as shown in Fig. 5 (a)᧩(c), while dynamic recrystallization arises at the high strain rates, as shown in Fig. 5 (d). For example, in the present study, as compared to the as-received 7A09 sample, the compressed 7A09 sample exhibits the dominant dynamic

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recrystallization at the deformation temperature of 460

, as shown in Fig. 6. It can be observed

from Fig. 6 (a) that in the as-received microstructure of 7A09 aluminum alloy, the grains are obviously elongated along the axial direction, which means that aluminum alloy bar is subjected to plastic working. However, it can be found from Fig. 6 (b) that in the microstructure of 7A09 aluminum alloy subjected to compression at the high strain rate of 10 s-1, the grains exhibit the equiaxed ones, which means that dynamic recrystallization prevails. It can be generally accepted that dynamic recrystallization is difficult to take place in the aluminum alloy with high fault energy. However, there have been the literatures [24-26] demonstrating that dynamic recrystallization can occur during hot working of aluminum alloy at the high strain rates. The mechanism of dynamic recrystallization of 7A09 aluminum alloy during hot compression deformation can be described as follows. It is generally accepted that the recrystallized grains firstly nucleate at the local region which possesses a high density of dislocations in the initial microstructure subjected to a certain plastic deformation degree, and then they grow up with the increase in the plastic strain. With the progression of the plastic deformation, the recrystallized grains stop growing and undergo a certain plastic deformation. Consequently, the new crystal nuclei occur at the local region with a high density of dislocations in the recrystallized grains formed previously, and thus the new recrystallized grains arise repeatedly until the plastic deformation finishes. It can be concluded that dynamic recrystallization is characterized by repeated nucleation and finite growth of the recrystallized grains. On the one hand, the high strain rates lead to the rapid increase in the dislocation density and consequently have an adverse influence on climb and cross-slip of the dislocations. Therefore, dynamic recovery can not be performed sufficiently and thus the increase in the energy storage is caused. On the other hand, the

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high strain rates cause the great temperature effect and consequently the heat quantity from plastic deformation work is unable to dissipate rapidly. The temperature effect similarly leads to the sharp temperature rise in the aluminum alloy, which can be validated by the experimental results as shown in Fig. 7. Fig. 7 indicates the curves of the temperature rise versus the time during hot compression of 7A09 aluminum alloy at the different strain rates at 400

. It can be found from

Fig. 7 that there is no temperature rise at the low strain rates of 0.01 s-1 and 0.1 s-1 and there is slight temperature rise at the strain rate of 1 s-1. However, there is sharp temperature rise at the strain rate of 10 s-1. The influence of the strain rate on the temperature rise can be explained as follows. In the case of the high strain rate, the thermal energy derived from the plastic deformation work can not be diffused outward in time and consequently the temperature increases rapidly. However, in the case of the low strain rate, the thermal energy derived from the plastic deformation work has sufficient time to dissipate and thus the temperature does not exhibit the sharp increase. It can be proposed that the energy storage and the temperature rise are responsible for dynamic recrystallization of 7A09 aluminum alloy at the high strain rates. 4.2. Constitutive equation According to the true stress-strain curves of 7A09 aluminum alloy as shown in Fig. 5, it can be found that the flow behavior of 7A09 aluminum alloy under hot deformation is related closely to the strain rates and the deformation temperatures. It is necessary to establish the constitutive equation in order to obtain mathematical description of the constitutive behavior of 7A09 aluminum alloy. The constitutive equation of 7A09 aluminum alloy is based on the Arrhenius type equation [27, 28].

H

A[sinh(DV )]n exp(

9

Q ) RT

(1)

Where H is the strain rate, V is the flow stress, T is the absolute temperature, Q is the activation energy, R is the universal gas constant ( 8.314J ˜ mol-1 ˜ K -1 ) ), and A , D and n are the material constants. In order to further obtain the material constants in Eq. (1) according to the experimental data, it is necessary to simplify the Eq. (1) mathematically [29]. When the low stress level leads to DV  1 , Eq. (1) can be simplified as

H

Q ) RT

A1V n exp(

Where A1 remains the material constant and A1

(2)

AD n .

When the high stress level results in DV ! 1.2 , Eq. (1) can be approximately expressed as

Q ) RT A Where A2 and E remain the material constant and A2 , E 2n

H

A2 exp( EV ) exp( 

(3)

nD .

The values of A , D , n and Q can be determined according to the experimental data and thus the constitutive equation of 7A09 aluminum alloy can be obtained. To obtain the value of n , the natural logarithm of Eq. (2) results in Eq. (4).

ln H

ln A1  n ln V 

Q RT

(4)

It can be seen from Eq. (4) that n is the linear proportion factor of ln H with respect to

ln V and thus can be determined by the slope of the lines derived from linear fitting method in Fig. 8 (a). The value of n is calculated as the average values of slope of the lines at the different deformation temperatures and thus is determined as 6.3141. In the same manner, in order to obtain the value of D , the value of E is firstly determined according to the natural logarithm of Eq. (3), which leads to Eq. (5).

lnH

lnA2  EV 

10

Q RT

(5)

Eq. (5) indicates that E is the linear proportion factor of ln H with respect to V and thus can be determined by the slopes of the lines derived from linear fitting method in Fig. 8 (b). The value of E is calculated as the average value of slope of the lines at the different deformation temperatures and thus is determined as 7.8325 u 102 MPa-1. As a result, the value of D can be obtained by combining the values of n and E , namely D

E / n 1.24 u102 MPa-1.

To obtain the value of Q , the natural logarithm of Eq. (1) results in the following equation.

lnH lnA  nln[sinh(DV )] 

Q RT

(6)

Based on Eq. (6), the value of n is modified as the linear proportion factor of ln H with respect to ln[sinh(DV )] . The value of n is determined as 4.906 according to the average value of slope of the lines at all the different deformation temperatures as shown in Fig. 8 (c). For the given strain rates, differentiating T

Q

1

in Eq. (6) results in Eq. (7)

§ w ln[sinh(DV )] · nR¨ ¸ wT 1 © ¹H

(7)

The value of Q can be calculated as 101.3 u103 J·mol-1 by combining the values of n and R with the average value of slope of all the lines at the different strain rates as shown in Fig. 8 (d). In general, the Zener-Hollomon parameter Z can be used to describe the comprehensive influence of the strain rate and the temperature on the flow stress of the metal materials during hot deformation [29].

Z

H exp(Q / RT )

A[sinh(DV )]n

(8)

The natural logarithm of Eq. (8) results in

ln Z

ln A  n ln[sinh(DV )]

(9)

According to Eq. (9), the value of ln A is the intercept of the fitting line of ln Z with respect to

ln[sinh(DV )] in the ln Z coordinate axis as shown in Fig. 9, so the value of A is further 11

determined as 1.48 u 107 s-1. By substituting the values of A , D , n and Q into Eq. (1), the constitutive equation of 7A09 aluminium alloy is expressed as follows.

H 1.48 u 107 [sinh(0.0124V )]4.906 u exp(101.3 u 103 / RT )

(10)

The substitution of Eq. (10) into Eq. (8) leads to

Z

H exp(Q / RT ) 1.48 u 107 [sinh(0.0124V )]4.906

(11)

According to Eq. (8), the following formulation can be obtained. 1

Z sinh(DV ) ( ) n A

(12)

According to the definition of the hyperbolic sinh(DV ) , Eq. (12) can be transformed into the following expression. 1

Z [exp(DV )]2  2( ) n exp(DV )  1 0 A

(13)

Eq. (13) can be further expressed as follows.

V

ª Z º Z ln «( )1 / n  ( ) 2 / n  1» D ¬ A A ¼ 1

(14)

In terms of the Zener-Hollomon parameter Z , the constitutive equation of 7A09 aluminium alloy is expressed by

V

1 / D ln{( Z / A)1 / n  [( Z / A) 2 / n  1]1 / 2 } 80.645 ln{[ Z /(1.48 u 107 )]0.2038  {[ Z /(1.48 u 107 )]0.4076  1}1 / 2 }

(15)

The constitutive equation can be used to describe the flow behavior of 7A09 aluminium alloy during hot deformation based on dynamic recovery and dynamic recrystallization. The constitutive equation of 7A09 aluminium alloy can be determined as the material model during finite element simulation of isothermal precision forging of aluminum alloy rotating disk.

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5. Hot processing map 5.1. Fundamentals of hot processing map According to dynamic material modeling, the power dissipated during plastic working of the metal material can be described by the following formulation.

GJ

P

(16)

Where G is the dissipated content expressed by H

³ VdH

G

0

(17)

and J is the dissipated co-content expressed by

³

J

V

0

HdV

(18)

It can be generally accepted that the flow behavior of metal materials is strongly dependent on the strain rate and the temperature. The general form of the flow behavior at the given strain and temperature is expressed as

V

KH m

(19)

Where K is the constant and m is the strain rate sensitivity which can be calculated as follows [30].

m

HdV VdH

dJ dG

HVd ln V ' lg V | VHd ln H ' lg H

(20)

At the given strain and temperature, the dissipated co-content J can be expressed by the following equation.

J

m VH m 1

(21)

It can be emphasized that Eq. (21) is based on the constant m . In general, the m value varies nonlinearly with the temperature and the strain rate. When the m value is equal to 1, the metal material belongs to the perfectly linear dissipation state, in which the dissipated co-content

J amounts to the maximum value J max [31]. 13

J max

VH 2

(22)

According to the combination of Eq. (21) and Eq. (22), the efficiency of power dissipation

K can be obtained as follows. K Where

J J max

2m m 1

(23)

K is closely related to the temperature, the strain and the strain rate. At the given strain,

the isoline map of

K with respect to the strain rate H and the temperature T can be plotted to

obtain the power dissipation map. The power dissipation map represents the relative rate of internal entropy production during hot deformation and characterizes the dissipative microstructure in the case of the different temperatures and the different strain rates [17]. However, in the power dissipation map, the large

K value represents either the zones of the good

workability or the zones of the unstable flow. Therefore, it is necessary to obtain the instability regimes of the plastic flow. Ziegler [32] firstly put forward the instability criterion of plastic flow by applying the extremum principle of irreversible thermodynamics to the plastic flow of large strain. Consequently, the stable flow will occur if the differential quotient satisfies the following inequality.

dD D ! dR R

(24)

Where R is the function of the strain rate, and D is the dissipation function at the given temperature. According to the dynamic material model, D is equal to J . Therefore, the flow instability criterion can be obtained as follows [33].

[ (H ) Where the parameter

§ m · w ln¨ ¸ © m 1¹  m  0 w ln H

(25)

[ (H ) may be viewed as a function of temperature and strain rate to obtain 14

an instability processing map. According to the instability processing map, metallurgical instability during plastic flow occurs in the regimes where

[ (H ) is negative. If the internal

entropy production rate in the material system is less than the strain rate imposed on the system, the flow becomes localized and causes flow instability. The hot processing map can be obtained by combining the power dissipation map and the instability processing map. 5.2. Establishment of hot processing map The flow stress used for establishing the hot processing map can be obtained by means of the isothermal compression test, as shown in Table 2. According to the data illustrated in Table 2, the relationship between lg V and lg H can be obtained, as shown in Fig. 10. The relationship between lg V and lg H can be fitted by means of cubic spline. Simultaneously, the strain rate sensitivity m can be calculated according to Eq. (20). As a result, the efficiency of power dissipation

K can be further calculated according to Eq. (23). Therefore, the power dissipation

map with respect to T and lg H can be established in the case of the different true strains, as shown in Fig. 11. Furthermore, the values of

[ based on the different temperatures and the

different strain rates can be obtained by substituting the values of lg H and m into Eq. (25). Consequently, the instability processing map of 7A09 aluminium alloy can be established through the interpolation method, as shown in Fig. 12. In the end, the hot processing map of 7A09 aluminium alloy can be obtained by means of superimposition of the power dissipation map and the instability processing map, as shown in Fig. 13. It can be found that the power dissipation generally decreases with the increase in the strain, while the instability flow zone gradually expands. If 7A09 aluminium alloy is subjected to plastic deformation in the case of the process parameters corresponding to the instability flow zone, microstructural defects are possible to take

15

place. Therefore, it is necessary to avoid hot working of 7A09 aluminium alloy within the instability flow zone. In the present study, the hot processing map is used for optimizing the process parameters to guarantee the stable flow zone of the metal material, such as the strain rate and the deformation temperature. In the case of large plastic deformation, when the strain rate is less than 0.1 s-1, 7A09 aluminium alloy shall exhibit the more stable flow. In addition, it seems that 7A09 aluminium alloy is characterized by steady flow in the temperature range from 300 460

to

. The processing map lays a certain foundation for the optimum working conditions on the

basis of flow stress, strain rate and deformation temperature. The establishment of the processing map based on the microstructural defects shall be investigated in the future. 6. Finite element simulation DEFORM3D commercial finite element code was used for simulating isothermal precision forging of rotating disk based on ring preform and pentagram preform. The deformation temperature is determined as 430

and the die moves at the velocity of 0.1 mm·s-1 during finite

element simulation. Fig. 14 indicates finite element simulation results of isothermal plastic forming of rotating disk forging based on the different preforms. Fig. 14 (a) indicates the distribution of the equivalent strain derived from finite element simulation of isothermal forging of rotating disk forging based on ring preform. For the sake of better understanding the deformation mechanism of the forged sample, the forming process of the forged sample can be divided into three stages, namely upsetting, forming of inner ear and forming of outer ear. At the upsetting stage, the metal mainly flows along the radial direction and the ring wall of the forged sample thickens gradually. At the second stage, the inner ear impressions are firstly filled with the metal since they are nearer to the

16

preform, and simultaneously the metal continues to flow inside to form the flash. At the third stage, as the upper die continues to move down, the resistance force from the flash gutter of the inner ears gets larger and larger. As a result, the metal is forced to flow into the outer ear impressions along the radial direction to form five outer ears. The final simulation results reveal that four outer ear impressions are not full of metal. Fig. 14 (b) indicates the distribution of the equivalent strain derived from finite element simulation of isothermal forging of rotating disk forging based on pentagram preform. The shape of pentagram preform causes five outer ear impressions to be covered with the sufficient metal, so the metal mainly flows into the impressions along the axial direction. According to the flow characteristic of the metal, the forming process of the forged sample can also be divided into three stages, namely local forming, forming of outer ears and forming of inner ears. At the local forming stage, the metal flows into the impressions along the axial direction by means of backward extrusion. With the increase in the plastic strain, the metal flows outside along the radial direction until the outer ear impressions are completely filled and the corresponding flash is finished. Consequently, the resistance force from the flash gutter of the outer ears causes the metal to flow into the inner ear impressions along the radial direction. Finally, the inner ears are completed. As compared to ring preform, pentagram preform leads to more homogeneous plastic deformation and more appropriate metal flow. Therefore, the finished forging exhibits no defects and the perfect simulation result is obtained. 7. Experimental results Isothermal precision forging of the rotating disk was carried out on the hydraulic press of 50000 kN. The forging process was composed of preforging and finish-forging. Furthermore, preforging, including upsetting, punching and under-reaming, provided the ring preform and the

17

pentagram preform for finish-forging. During isothermal precision forging, the preform firstly was heated to 100

in the heating furnace and then was covered with colloidal graphite mixed with

water. Subsequently, the preform was reheated to 430 the dies were directly heated to 100

and was held for 1.5 h. Simultaneously,

on the hydraulic press and then were covered with colloidal

graphite mixed with water. Subsequently, the dies were reheated to 430

. Fig. 15 indicates the

finish-forging die used for isothermal precision forging of rotating disk. Fig. 16 illustrated the finished forgings by using the ring preform and the pentagram preform, respectively. It can be observed from Fig. 16 that in the case of the ring preform, the outer ears of the finished forging were incompletely filled, while in the case of the pentagram preform, the outer ears of the finished forging were completely filled. The experimental results are in good accordance with the simulated ones as shown in Fig. 14. It can be concluded that the appropriate control of the metal flow plays an important role in guaranteeing the perfect formability of the finished forging. 8. Conclusions 1) Based on computer-aided design (CAD), computer-aided engineering (CAE) and computer-aided manufacturing (CAM), isothermal precision forging plays a significant role in manufacturing complex-shape aluminium alloy rotating disk of airplane. 2) The constitutive equation of 7A09 aluminium alloy was established according to hot compression test at the temperatures ranging from 300

to 460

and at the strain rates ranging

from 0.01 s-1 to 10 s-1. The constitutive equation plays an important role in understanding the flow behavior of 7A09 aluminium alloy in the case of dynamic recovery and dynamic recrystallization. 3) It can be proposed that 7A09 aluminium alloy frequently exhibits dynamic recovery in the case of the low strain rates ranging from 0.01 s-1 to 1 s-1, while it is characterized by dynamic

18

recrystallization in the case of the high strain rate of 10 s-1. 4) The mechanism of dynamic recrystallization of 7A09 aluminum alloy during hot compression deformation can be based on the fact that the recrystallized grains firstly nucleate at the local region which possesses a high density of dislocations in the initial microstructure. Furthermore, dynamic recrystallization is characterized by repeated nucleation and finite growth of the recrystallized grains. 5) According to dynamic material model, the hot processing map of 7A09 aluminium alloy under hot deformation was obtained on the basis of the power dissipation map and the instability processing map. The hot processing map lays the foundation for optimizing the process parameters during isothermal precision forging. It can be concluded that in the case of large plastic deformation, 7A09 aluminium alloy exhibits the more stable flow at the strain rates less than 0.1s-1. 6) Based on ring preform and pentagram preform, finite element method (FEM) was used to simulate the metal flow and predict the forming defects during isothermal precision forging of rotating disk. The simulated results agree well with the experimental ones. As compared to the ring preform, the pentagram preform contributes to the flow of the metal material along the axial direction during isothermal precision forging and consequently the complete die filling can be performed. In the end, on the basis of the pentagram preform, the qualified rotating disk forging is obtained by means of digitized technology. References [1] D. B. Shan, W. C. Xu, C.H. Si, Y. Lu, J. Mater. Process. Technol. 187–188 (2007) 480–485. [2] D.B. Shan, F. Liu, W.C. Xu, Y. Lu, J. Mater. Process. Technol. 170 (2005) 412–415.

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[3] Y.Q. Zhang, D.B. Shan, F.C. Xu, J. Mater. Process. Technol. 209 (2009) 745–753. [4] P. Petrov, V. Perlov, S. Stebunov, J. Mater. Process. Technol. 177 (2006) 218–223. [5] M. Jackson, N.G. Jones, D. Dye, R.J. Dashwood, Mater. Sci. Eng., A 501 (2009) 248–254. [6] B. Lu, H. Ou, C.G. Armstrong, A. Rennie, Mater. Des. 30 (2009) 2490–2500. [7] S. H. Huang, Y.Y. Zong, D.B. Shan. Mater. Sci. Eng., A 561 (2013) 17–25. [8] K.K. Deng, X.J.Wang, W.M. Gan, Y.W.Wu, K.B. Nie,K.Wu, M.Y. Zheng, H.G. Brokmeier. Mater. Sci. Eng., A 528 (2011) 1707–1712. [9] M. Arbak, A. Erman Tekkaya, F. Ozhan, J. Mater. Process. Technol. 169 (2005) 72–82. [10]L. Cecchetto, A. Denoyelle, D. Delabouglise, J.P. Petit, Appl. Surf. Sci. 254 (2008) 1736–1743. [11]P. Hartley, I. Pillinger, Comput. Methods Appl. Mech. Eng. 195 (2006) 6676–6690. [12]K.P. Rao, Y.V.R.K. Prasad, K. Suresh. Mater. Des. 32 (2011) 2545–2553. [13]Y.V.R.K. Prasad, K.P. Rao. Mater. Des. 32 (2011) 1851–1858 [14]A. Momeni, K. Dehghani. Mater. Sci. Eng., A 528 (2011) 1448–1454 [15]Y.V.R.K. Prasad, S. Sasidhara, V.K. Sikka, Intermetallics 8 (2000) 987–995. [16]G. Ganesan, K. Raghukandan, R. Karthikeyan, B.C. Pai, J. Mater. Process. Technol. 166 (2005) 423–429. [17]S. Ramanathan, R. Karthikeyan, G. Ganasen, Mater. Sci. Eng., A 441 (2006) 321–325. [18]C.Y. Wang, X.J. Wang, H. Chang, K. Wu, M.Y. Zheng, Mater. Sci. Eng., A 464 (2007) 52–58. [19]T.K. Ha, J.Y. Jung, Mater. Sci. Eng., A 448-451 (2007) 139–143. [20]V. Gopala Krishna, V.Y.V.R.K. Prasad, N.C. Birla, G. Sambasiva Rao, J. Mater. Process. Technol. 71 (1997) 377–383.

20

[21]G. Zhou, H. Ding, F. R. Cao, Y. B. Han, B.J. Zhang. Trans. Nonferrous Met. Soc. China 22 (2012) 1575–1581. [22]M. Morakabati, M. Aboutalebi, Sh. Kheirandish, A. Karimi Taheri, S.M. Abbasi. Intermetallics 19 (2011) 1399–1404. [23]S.Y. Jiang, Y.Q. Zhang, Y.N. Zhao. Trans. Nonferrous Met. Soc. China 23(2013) 140147. [24]N.P. Jin, H. Zhang, Y. Han, W.X. Wu, J.H. Chen. Mater. Charact. 60 (2009) 530–536. [25]G.S. Fu, K.W. Qian, W.Z. Chen, J.X. Kang, Trans. Nonferrous. Met. Soc. China (2000) 671–674. [26]H. Zhang, N.P. Jin, J.H. Chen. Trans. Nonferrous Met. Soc. China 21(2011) 437442. [27]H.R. Rezaei Ashtiani

M.H. Parsab,

H. Bisadi. Mater. Sci. Eng., A 545 (2012) 61–67.

[28]H.J. Mcoueen, N.D. Ryan, Mater. Sci. Eng., A 322 (2005) 43–63. [29]S.Y. Jiang, Y.Q. Zhang, Y.N. Zhao, M. Tang, W.L. Yi, J. Cent. South Univ. 20 (2013) 24–29. [30]S. Anbu Selvan, S. Ramanathan, Trans. Nonferrous. Met. Soc. China 21 (2011) 257–264. [31]W.D. Zeng, Y.G. Zhou, J. Zhou, H.Q. Yu, X.M. Zhang, B. Xu, Rare Metal Mat. Eng. 35 (2006) 673-677. [32]H. Ziegler, L.K. Yu, Ingenieur. Archiv. 41 (1972) 89–99. [33]H.Y. Kim, H.C. Kwon, H.W. Lee, Y.T. Im, S.M. Byon, H.D. Park, J. Mater. Process. Technol. 205 (2008) 70–80.

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Tables Table 1 Chemical composition of 7A09 aluminum alloy (%᧨mass fraction). Cr

Mn

Si

Cu

Zn

Mg

Ti

Fe

Al

0.23

0.081

0.063

1.49

5.8

2.8

0.024

0.45

balance

Table 2 The values of the flow stress of 7A09 aluminium alloy (MPa). Temperature, Strain

-1

Strain rate᧨s

300

350

400

430

460

0.01

68.9

55.2

44.7

41.4

30.1

0.1

116.8

85

85.4

62

48.6

1.0

145.8

117.4

94.2

81.5

74.4

10

157.7

138.1

115.1

108.6

99.9

0.01

76.6

58.7

46.3

43.1

31.4

0.1

110.6

87.9

71.1

66

50.3

1.0

139

117.8

98

89.4

76.7

10

153.5

134.9

114.7

108.9

97

0.6

0.8

22

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16