AZ31B鎂合金板材進(jìn)行重復(fù)單向彎曲過程的冷沖壓成形性外文文獻(xiàn)翻譯、中英文翻譯

1、Cold stamping formability of AZ31B magnesium alloy sheet undergoing repeated unidirectional bending processLei Zhanga,b, Guangsheng Huanga,b, * , Hua Zhanga,b , Bo Song a,ba National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400030, Chinab College of Material

2、Science and Engineering, Chongqing University, Chongqing 400030, China-a r t i c l e i n f o-Article history:Received 11 April 2010Received in revised form 7 November 2010Accepted 28 November 2010Available online 7 December 2010-a b s t r a c t-The repeated unidirectional bending (RUB) process was c

3、arried out on an AZ31B magnesium alloy in order to investigate its effects on the cold stamping formability. The limiting drawing ratio (LDR) of the RUB processed magnesium alloy sheet with an inclination of basal pole in the rolling direction can reach 1.5 at room temperature. It was also conrmed t

4、hat cell phone housings can be stamped successfully in crank press using the RUB processed AZ31B magnesium alloy sheet. The improvement of the stamping formability at room temperature can be attributed to the texture modications, which led to a lower yield strength, a larger fracture elongation, a s

5、maller Lankford value (r-value) and a larger strain hardening exponent (n-value). 2010 Elsevier B.V. All rights reserved.Keywords: Magnesium alloy sheet;RUB;Texture;Stamping formability；Cell phone housing1. IntroductionNowadays, the products of magnesium alloys, mainly formed by casting and die-cast

6、ing, are used in the aerospace, automobile, civilian household appliances. Compared with casting and die-casting, plastic forming technology seems to be more attractive because of its competitive productivity and performance. Among the fabricationprocesses of plastic forming, stamping of magnesium a

7、lloy sheets is especially important for the production of thin-walled structural components (Chen and Huang, 2003). However, magnesium alloy sheets have low ductility at room temperature due to itsstrong (0002) basal texture, as shown in the literature (Doege and Droder, 2001). Mori and Tsuji (2007)

8、 investigated cold deep drawing of commercial magnesium alloy sheets, they demonstrated that the limiting drawing ratio of rolled AZ31 magnesium alloy sheetsannealed at 773 K can reach 1.7. Mori et al. (2009) have shown that a two-stage cold stamping process are also helpful for forming magnesium al

9、loy cups. Watanabe et al. (2004) suggested the ductility of magnesium alloy sheets can be improved by reducing (0002) basal texture at room temperature. The limiting drawing ratio for the cold deep drawing of commercial magnesium alloy sheets can be improved from 1.2 to 1.4 by reducing (0002) basal

10、plane texture (Iwanaga et al., 2004). It is well-known that equal channel angular pressing (ECAP) is an effective method to obtain a tilted basal texture, which improved signicantly the tensile elongation (Kim et al., 2003). But it is hard for ECAP to fabricate thin sheet. Recently, it is reported t

11、hat a rolled magnesium alloy sheet, with a tiled texture obtained by cross-roll rolling (Chino et al., 2006) and different speed rolling (DSR) process (X.S. Huang et al., 2009), exhibit higher stamping formability compared with a rolled magnesium alloy sheet by normal-roll rolling. It is therefore i

12、mportant to improve the formability at room temperature for a wide use of magnesium alloy sheets by changing or weakening the basal texture.Older versions of the ASM Metals Handbook (1969) on forming refer to a “special bending sheet,” which was produced by Dow Magnesium. The special bending sheet w

13、ith a modied crystallographic texture, had better forming characteristics than conventional AZ31 sheet. Previous study (G.S. Huang et al., 2009) revealed that the RUB process also improved the stretch forming of magnesium alloy sheets by weakening basal texture of sheets. The Erichsen values of the

14、RUB processed sheet signicantly increased from 3.53 to 5.90 in comparison with the cold-rolled magnesium alloy sheet. However, up to now, few researchers made efforts to study the cold stamping formability of the magnesium alloy sheets. Cold stamping products, such as housings of laptop computers an

15、d cell phones, have not been reported in other investigations. Hence, it is important to investigate the cold deformation behaviors so as to establish fundamental knowledge of the cold forming technology of magnesium alloy.In this paper, an investigation of the drawability of RUB processed AZ31 magn

16、esium alloy sheet was performed at room temperature using uniaxial tensile tests, deep drawing and cold stamping of a cell phone housing. The performance of RUB sheet was compared with that of the as-received sheet.2. Experimental material and procedure2.1. The preparation of experimental materialCo

17、mmercial AZ31B magnesium alloy sheets with a thickness of 0.8 mm, cut into 1000 mm 100 mm (length width) pieces, were used in the experiments. Fig. 1 shows the schematic diagram of the RUB process. The radius of the cylindrical support was 1 mm andthe bending angle was 90 . The magnesium alloy sheet

18、 was bent on a cylindrical support under a constant force T with a constant speed v. There was six-pass bending, which indicated that there were six bending operations in all at two orientations in the experiment. This meant that after each bending pass, the sheet was turned over and the bending ori

19、entation was also changed in the next pass. The RUB processed sheets were annealed at 533 K for 60 min, and then were subjected to tensile tests, deep drawing, and cold stamping of cell phone housing investigation.Fig. 1. Schematic diagram of the RUB process.Fig. 2. 0002 Pole gures of as-received sh

20、eet and RUB sheet. (a) as-RUB sample, max density = 8.66; (b) RUB sample, max density = 7.31.Previous studies (Song et al., 2010; Huang et al., 2010) have investigated microstructure and texture evolution of AZ31 magnesium alloy sheets underwent RUB. For the as-received sheet, the grains were ne. Af

21、ter the magnesium alloy sheet underwentRUB was annealed at 260 C, the grains near the surface of sheet grew obviously, while those in the central region had little growth. The average grain size of two state sheets was almost the same. Fig. 2 shows 0002 pole gures of two state sheets. The asreceived

22、sheets exhibit a strong basal texture, where the majority of grains are oriented with their0002 basal planes parallel to the rolling plane of the sheet. In contrast, the RUB processed sheets exhibit a large inclination of c-axis around the normal direction(ND) towards the RD, which weakens basal tex

23、ture of the sheet.2.2. Uniaxial tensile testsThe specimens for tensile tests had a parallel length of 57 mm, a width of 12.5 mm and a thickness of 0.8 mm. The specimens were cut along planes coinciding with at the angles of 0 (RD) and 45 and 90 (TD) to the rolling direction. Prior to testing, all sp

24、ecimens were polished by the abrasive paper to remove major scratches to avoid fracture occurring at an undesired location of the specimen. The uniaxial tensile tests were carried out on a CMT6305-300 KN testing machine with an initial strain rate of 3 10 -2 s -1 to examine the mechanic properties s

25、uch as the yield strength, the ultimate tensile strength and the fracture elongation. The strain hardening exponent values (n-value) were obtained by power law regression (_ = _e n ) of the tensile test data within a uniform strain of e =15%. The Lankford values (r-value), r= e w /e t , where the va

26、riables e w and e t denote the strains in the tensile specimens transverse and thickness directions, respectively, were measured on the specimens at a uniform plastic deformation of e =15%. 2.3. Limiting drawing ratio (LDR) tests To evaluate the deep drawability of the RUB processed AZ31 magnesium a

27、lloy sheet, limiting drawing ratio (LDR) tests were carried out on a 600 kN hydraulic press to examine the stamping formability at room temperature. The schematic diagram and geometry dimension of mold are shown in Fig. 3 and Table 1, respectively. Magnesium alloy sheets were processed into circular

28、 specimens with various diameter dimensions using wire-cutting. Before deep drawing, all circular specimens should be polished by the abrasive paper in order to avoid crack in them. Special positioning ring was adopted to x the specimens. A rigid blank holder was used on the molds, which can offer s

29、ufcient blank holder force to press the blank tightly by adjusting the spring. Consequently, theblank holder and die were uniformly lubricated with oil. The punch was not lubricated. Fig. 3. Schematic diagram of mold.Table 1 Parameters of punch and die used in the experiment.Punch diameter, d p(mm)P

30、unch shoulderradius, r p (mm)Die clearance,z (mm)Die shoulderradius, r d (mm)5051289.12.4. Cold stamping of cell phone housing The as-received sheets and the RUB processed AZ31 magnesium alloy sheets with a thickness of 0.6 mm were used in these experiments; three sets of stamping dies for cell phon

31、e housing manufacture were used, the blanking die, deep drawing die and piercing die. Compared with the blanking and piercing die, the structure of deep drawing die was more complex. The main parameters of deep drawing die were as follows: punch radius r p = 1 mm; die radius r d = 2 mm; die clearanc

32、e in the straight wall C = 0.6 mm; die clearance in the corner C = 0.66 mm. The three sets of dies driven by the crank press completed the blanking, the deep drawing and the piercing process in turn.Fig. 4. The true stressstrain curves of the as-received specimens and the RUB processedspecimens in t

33、he tensile directions of RD, 45 and TD (RD, rolling direction;TD, transverse directions).3. Results3.1. Mechanical propertiesFig. 4 shows that the true stressstrain curves of the as-received specimens and the RUB processed specimens in the tensile directions of RD, 45 and TD. Compared with the as-re

34、ceived specimens, the RUB processed specimens exhibit larger in-plane anisotropy,and the signicant differences can be observed from the true stressstrain curves at the beginning stage of the tensile deformation. The work-hardening effects are stronger for the tensile specimens in the tensile directi

35、ons of RD, 45 and TD after the yield deformation. The yield strength, tensile strength and the fracture elongation are shown in Fig. 5. The tensile strengths of the RUB processed specimens are nearly the same as that of the as-received specimens regardless of the tensile directions. While yield stre

36、ngth of the RUB processed specimens is signicantly lower than that of the as-received specimens especially in the RD. These results indicate that the RUB process has a strong effect on the yield strength but not the tensile strength. Additionally, the fracture elongations of the RUB processed specim

37、ens are improved in the tensile directions of RD, 45 and TD in comparison with those of the as-received specimens, especially in the RD with the largest increase from 19.2% to 26.7%. These are mainly due to the RUB processed spec-imens with stronger work-hardening effects which contribute to the inc

38、rease in the fracture elongation. Above all, the inclination of the c-axis toward the RD lowers the yield strength but elevates work-hardening effects which contribute to improve the uniform elongation.The r-value and the n-value of the as-received specimens and the RUB processed specimens are shown

39、 in Fig. 6. Compared with the as received specimens, the RUB processed specimens show a much smaller r-value and a larger n-value especially in the RD, which decreases from 2.15 to 0.92 and increases from 0.20 to 0.29, respectively.The difference between r-values as well as that between n-values of

40、the as received specimens and the RUB processed specimens decreases with increasing the tensile angle. The average r-value ( r = (r RD + 2r 45 + r TD )/4) falls from 2.45 to 1.36, and the average n-value ( n = (n RD + 2n 45 + n TD )/4) rises from 0.175 to 0.225 in comparison with those of the as-rec

41、eived specimens. The decrease in r indicates that it is easier to reduce or increase the thickness of sheet during the plastic deformation. Furthermore, the improvement in the fracture elongation was mainly due to the high n which resulted in a low sensitivity to strain localization in theform of ne

42、cking. Fig. 5. (a) Tensile strength and yield strength, (b) fracture elongation of the as-received specimens and the RUB processed specimens in the tensile directions of RD, 45 andFig. 6. r-Value and n-value of the as-received specimens and the RUB processedspecimens in the tensile directions of RD,

43、 45 and TD.3.2. LDR Drawing ratio (DR) is commonly expressed by RD = d 0 /d p , where d 0 and d p are the blank diameter and punch diameter, respectively. The LDR is the one when the specimen is on the verge of fracture. Fig. 7 shows cold deep drawn cups of the as-received specimens and the RUB proc

44、essed specimens for DR = 1.5. The as-received specimens fractured at the punch shoulder, and the drawing depth was only 7.2 mm. However, the drawn cup of the RUB processed specimens showed a good appearance at a drawing depth of 11.8 mm. Compared with the as-received specimens, the RUB processed spe

45、cimens show better stamping formability. These are mainly due to the RUB processed specimens with a tiled texture, which contribute to the increase in the drawing depth. If the drawing depth went up to 14.8 mm, the fracture occurred at the edge of the ange for the RUB processed specimens during deep

46、 drawing. Yang et al. (2008) investigated die as shown in Fig. 8(a), the force was not applied onto the edge using the at blank holder. To apply the force onto the edge even in passing though the die corner, the blank holder was exchanged forthat having a ring-shaped projection in an intermediate st

47、age of the deep drawing as shown in Fig. 8(b) (Mori and Tsuji, 2007). Additionally, for magnesium alloy sheets, the fracture happened in the top of the cup during bendingunbending as the material passes over the die radius. Those previous observations point out that compared with aluminum-alloy shee

48、ts (including AA2024, 6061,7075), magnesium alloys exhibit poor bending ductility due to their strong in-plane anisotropy and mechanical twinninginduced tensioncompression strength asymmetry in two sides of the bending blank (Agnew et al., 2006). The blank holder with a ring-shaped projection is emp

49、loyed instead of the at bank holder after the edge of the ange breaking out of the at bank holder, which is helpful to improve unbending ductility of the sheet in the die corner. Fig. 9 shows cold deep drawn cup using the blank holder with a ring-shaped projection in an intermediate stage of thedeep

50、 drawing as shown in Fig. 8(b). The LDR of the RUB processed specimens is 1.5 under present experimental conditions. However, compared to a circular cup deep drawing, the depth of cell phone housing is only 6 mm, thus the subsequent cold stamping processof cell phone housing is carried out using one

51、-step and at blank holder.Fig. 7. Cold deep drawn cups with different drawing depth of as-received specimen and the specimen undergoing RUB process for DR = 1.5.Fig. 8. The edge of the blank passes though the corner of the die at different pressure situations: (a) No blank holder force; (b) action o

52、f blank holder force.Fig. 9. Cold deep drawn cup using the blank holder with a ring-shaped projection.Fig. 10 shows the thickness strain at the angles of 0 (RD), 45 and 90 (TD) to the rolling direction of cold deep drawn cup for the RUB processed specimens. The valleys of the curves represent the se

53、ctions of the cup corners. Despite of the different r-values in thethree directions, the values at the cup corners are approximately the same. It is well known that the stresses in the hoop directions around the ange of the cup resulted in the increase in thickness during deep drawing. For the RUB p

54、rocessed sheets with a tilted basal texture, the thickness strain can be generated by basal slip.Fig. 10. Distributions of wall thickness strain of drawn cups for = 1.5.3.3. Cold stamping of cell phone housingsPreliminary experimental results demonstrate that the RUB process has an important inuence

55、 on the stamping formability of AZ31 magnesium alloy sheets. Fig. 11 shows the results of cold stamping of cell phone housings. The as-received specimen was drawn unsuccessfully, as shown in Fig. 11(a). It can be found that the critical section at the punch shoulder was broken before the ange of the

56、 specimen was fully dragged into the die cavity. While the RUB processed specimen was drawn successfully, the critical section at the punch shoulder and the ange was excellent, as shown in Fig. 11(b). The experimental results show that the RUB process improved the shallow drawing formability of magn

57、esium alloy sheets. Besides, certainly, cell phone housings can be obtained successfully in crank press using the RUB processed AZ31 specimens by the cold stamping process.Fig. 11. The results of cold stamping of cell phone housings: (a) as-received sample;(b) the RUB processed specimen.4. Discussio

58、nG.S. Huang et al. (2009) revealed that mechanical properties and stretch formability of magnesium alloy sheets with a tilted basal texture obtained by the RUB process were improved at room temperature. Agnew and Duygulu (2005) and Koike et al. (2003) havenoted that for magnesium alloy sheets with a very strong basal texture, the width strain e w can be gene