completed。 As compared to ring preform, pentagram preform leads to more homogeneous plastic deformation and more appro- priate 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 50,000 kN。 The forging process was composed of preforging and finish-forging。 Furthermore, prefor- ging, including upsetting, punching and under-reaming, provided the ring preform and the pentagram preform for    finish-forging。

During isothermal precision forging, the  preform  firstly  was heated  to  100 1C  in  the  heating  furnace  and  then  was  covered

with colloidal graphite mixed with water。 Subsequently, the pre- form was reheated to 430 1C and was held for 1。5 h。 Simulta- neously, the dies were directly heated to 100 1C on the hydraulic

Fig。 14。  Finite element simulation results of isothermal forging of rotating disk based on the different preforms: (a) ring preform and (b) pentagram   preform。

Fig。 15。  The finish-forging die for isothermal precision forging of rotating disk: (a) top die and (b) bottom die。

press and then were covered with colloidal graphite mixed with water。  Subsequently,  the  dies  were  reheated  to  430 1C。  Fig。  15

indicates the finish-forging die used for isothermal precision forging of rotating disk。 Fig。 16 illustrates 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 engineer- ing  (CAE)  and  computer-aided  manufacturing  (CAM), isothermal

precision forging plays a significant role in manufacturing complex-shape  aluminum  alloy  rotating  disk  of airplane。

(2)The constitutive equation of 7A09 aluminum alloy was estab-

lished according to hot compression test at the temperatures ranging from 300 1C to 460 1C 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 aluminum alloy in the case of dynamic recovery and dynamic recrystallization。

(3)It can be proposed that 7A09 aluminum 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    recrystalliza-

tion 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 charac- terized by repeated nucleation and finite growth of the recrys- tallized grains。

Fig。 16。  Photographs of rotating disk forgings based on the different preforms: (a) ring preform and (b) pentagram   preform。