AN INVESTIGATION ON THE CREEP BEHAVIOR OF PURE Mg

Ù Ù 11 Vol. No.11 008 «11 Ù 135 1359 «ACTA METALLURGICA SINICA Nov. 008 pp.135 1359 Mg ²» ¼ (Đ Ý Ê ß Ï Ö Đ ÑÛ Ö, 11189) ( ß ³ ¼, 111) ¾ ß Â Mg Ø 75 00, 15 0 MPa ĐÈ Þ: Ò ĐÈ, Ú Ø ÈÈ, ÅÕ; Ó Ø ¹, È Æ, ÈÏ; ¹ Ê ¹ È, È ¼Ò.» Ú ½, Ú Â Mg Ø ÅÕ Ê, Ê n ¹.3.9, ű Ê, n >7; 76.0 89. kj/mol.» Ê Ã ± Å Ã,  Mg Ü Î Æ ÎÆ Í, Î Æà ÎÆÄÖ.  Mg,, Î Æ, ÎÆ TG111.8, TG16. ¹º ± A ¹ 01 1961(008)11 135 06 AN INVESTIGATION ON THE CREEP BEHAVIOR OF PURE Mg YAN Jingli, SUN Yangshan, XUE Feng Jiangsu Key Laboratory for Advanced Metallic Materials, Southeast University, Nanjing 11189 TAO Weijian Nanjing Welbow Metals Co.,Ltd., Nanjing 111 Correspondent: SUN Yangshan, professor, Tel: (05)5090689 0, E-mail: yssun@seu.edu.cn Supported by Natural Science Foundation of Jiangsu Province (No.BK0008) and the Foundation for Excellent Doctoral Dissertation of Southeast University Manuscript received 008 0 1, in revised form 008 08 06 ABSTRACT The creep behaviors of pure Mg in different states at the temperature range of 75 00 under the stress range of 15 0 MPa were studied. The results indicate that the grain size has remarkable effect on the creep behavior. The as cast Mg with coarse column grains has low creep rate. However, the creep rate increases significantly as the grains become fine equiaxed due to dynamic recrystallization after extrusion, and decreases when the grains coarsen after annealing. The stress exponents n lie in a range of.3.9 under low stresses, which is corresponding to dislocation climb mechanism. However, the n values are over 7 under high stresses. The apparent activation energies range from 76.0 to 89. kj/mol. According to the stress exponents and the activation energies as well as the microstructure analysis during creep, the creep are affected by dislocation climb, grain boundary sliding and twinning, among which the former two mechanisms play dominant role. KEY WORDS pure Mg, creep, dislocation climb, grain boundary sliding ÖÆ ÔÙ Å Ç Ð º. ½µ Ä ² Û ÓÖÁ Þ Ö ÞÅ * Å Þ BK0008 Ã Þ Ø³ Þ Ù Û ³ : 008 0 1, Û ³ : 008 08 06 ÊÞ : ²Å,, 1981 Í, ³ Í Ë µ ܺÖÁÓ Ü, Þ À Ó ¾ÃÍÎ ²³. «, ÖÆ Ö «, ², Ä Ö É, «² Ý, ÖÆ À. Đ², ¼ßË Ö Æ ¹ Ü ¼Î Í Ý [1 ]. Ö Ô ÖÆ ² Ö Â. ¼º ß ² Ö Æ ÑÖ

u 11 Æ%Lm : I Mg ie p8, 1355 :G >rn 7KV\Uk., & 6hV g G k S _ Li^, qg ed k. gj k< C, ) g W * J 5 Y C - L aq k s ) C. 9 G 5 <E. <, O Q, -R: a h f r k ), 6 X p r N C& > k L. Q k G E l? d G E k 5 <edz q ) C -K Mg C 75 00 (0.38 0.51 T, T tj, CJlQZ) )$> yl S! Q k 9C x) k G E, " E G f 1 > S Xy G q9 qnjk q. : M k Q< d k, & N G E i 5 < Z K Mg k! 6 9uÆ` (a=0.31 nm, c= Yk L, E* VK Mg CN> ykg q9l 0.51 nm), s> r r. K Mg ^! k ) S a G e J. ).8.9 MPa,! k( L O r, N) 1 '1 [! 6. Y. <, C jr N G q9 k 0! kk Mg w } % # ;G l } 9 ) f,!ok Mg 7f. a)oivk Mg kg ed, Y /, K >99.90%, N GB399 003 k /= J N 5 kxj rn G q9 k, 9 ~. p } p C 315 t & } e Q q, Y (w }) > 7Æjm >rn CJlQ! _!. ~ 9 360, p }%> ~ 9 350, p } 9 9 # 9`,.K Mg kg q9k -&). 1, p } S k u S I:.. ` H J C CO " i ) k f\ C Ql v 80 &, * V O, & : q,. ` > 9 500, ` y $ 9 1 L 3 h, a h V1 Y< { y k 5 d. Shi L Northwood ))$!Q ku.!.g ku 0!Bw!~ Jones o Vagarali L Langdon C -K Mg kg (GB/T039 1997) ~ko LBU (!9 100 mm, `, hf<w pg k?ded; Roberts C [+ 10 mm). G C RD 3 m&>g eq -i({v! W CG v Æ k!; Milic ka q, >?dc ±1 k 7. T5 Z0!>{T o G 9 d xqm< Wk) = ( Æ > m< W 5* (OM) LMyz* (SEM) <, G E k5< O d x J } x W M k W l y< W Y d k 6 Y<C JEOL JEM000EX m(sz* (TEM) } x< W W > = pg f? ded. $`, Q q. ) k - \ p V O }G q9 k - C, '1 O>S{k, >! Power Law (w_ ) s + 1a 9K Mg kw Z. %+i= 9F, K [5 7] m [8] [9] [10] [11] [1] + J js Y (a) as cast (b) as extruded 1 Mg Fig.1 Microstructures of pure Mg (c) annealed for 1 h after extrusion (d) annealed for 3 h after extrusion m

1356 Þ Ü Ù Mg Û ±É Ø, Ø 1 mm, µ, 50 00 µm Ý. ÔÐË, Ù ½ Î, Ì Ç ÓÓ, É Í 30 0 µm, Á 1b. 1c Ä d ÔÐË Ã Mg 1 Ä 3 h º ÀÂË., º ÀÂË, Ç ÓÓ µµ, É Í 100 Ä 00 µm «. Îà Mg Û Ù 15, 0 0 MPa. Ç, «Ö ËÉ, Ò, «Ö ÚÇ Ý. Ë ÀÜ, ÍÕ ÀÜ, Ú 1 Æ Ú Ý «ÍÀ, Ú Æ Ú ÝÅÕ, Ç Â Ú 3 Æ. ε s Æ. à Mg Û Ù 75 00, 15 0 MPa 1. Ç ¹ßÌØ, à Mg Ö Ç, 150, 0 MPa É, 5.67 10 8 s 1. Ä/ Ë À Ü, À. µ É Ã Mg 150, 0 MPa Á 3a, 3b ( )., Ú 1 Æ Ñ É, ²Õ ½ºÈ, «Â Æ. ² Creep strain s, % Creep strain s, % 8 6 0 5 3 1 (a) 0 MPa 5 MPa 30 MPa 35 MPa 0 MPa 0 0 0 60 80 100 10 10 160 Time, h (b) 90 min 15 min 0 0 50 100 150 00 50 300 350 Time, min Ú Â Mg 15, 0 0 MPa Fig. Creep curves of as cast pure Mg specimen at 15 under the stress range of 0 0 MPa (a) and 0 MPa (b) 3a : Û Ã Mg Ù ½µÅÖ (5.67 10 8 s 1 ); 3 h º À ٠µ (5.7 10 8 s 1 ); «1 h º ÀÂ Ù É 7.83 10 8 s 1, ²Î 0%; Ô Ð Ù 1.58 10 7 s 1, º Û Ù 3. Î Î, Û Î½µ 3 µýñ Æ ( b) 90 min( ) Ä 15 min( Ë ) Ë ÕÎ ¾, Á. Ú 1 Æ, ܺ ÀÜ, µ É 1 Ü Ä Mg Ú 75 00 Å, 15 0 MPa Ð À Æ Table 1 Steady state creep rates of the as cast pure Mg at the temperature range of 75 00 under the stress range of 15 0 MPa (10 8 s 1 ) Temperature Stress, MPa 15 0 5 30 35 0 Creep strain s, % Creep rate s, 10-1 s -1 75 1.67 1.73 100 1.0.5 10.9 3.5 15 1.06.7 1.6 3. 19 150 1.3 5.67 1.5 66.5 38 636 175 5.86 1.5 59.7 00 1.8 (a) 10 As-cast. s,10-8 s -1 As-extruded 8 Annealed for 1 h 15.8 Annealed for 3 h 5.67 6 0 7.83 5.7-0 0 0 0 60 80 100 10 10 160 180 00 Time, h 50 (b) 00 150 100 8 6-0 0 0 0 60 80 100 10 10 160 180 00 Time, h 3 ß È Mg 150, 0 MPa Fig.3 Creep curves (a) and creep rate curves (b) of the pure Mg treated at different conditions

Ù 11 ƱÄÑ : Á Mg Ô Đ 1357 3 µ 5  Mg Ú Ø 15, 0 MPa Ê Fig.5 Microstructures of the as cast pure Mg specimen after creep at 15 and 0 MPa (a) optical photograph showing the wedge shaped crack at triple joint grain boundaries (b) SEM image showing the fracture morphology, ÐÄÆ ε s ½ Ë Å É Power Law À [1] : ε s = Aσ n exp( Q app /(RT)) (1)  Mg 15, 0 MPa È TEM È Fig. TEM photographs of the as cast pure Mg during steady state creep at 15 and 0 MPa (a) initial stage, dislocation cells (sub boundaries) formed, as shown by arrows (b) final stage, sub grains formed. Â Æ Ë, Ü Ïµ À Îܺ ; Ü, ¾¾, Ï Ó Ï ( a ³ ), ² ÙÚ ÕÓ, ÒÆ Î. ܺ Ä Ë Æ «Ö. Õ, Î Æ Ë, Ù Ó Î Í, Á b. à Mg Û Ù 15, 0 MPa Ë Á 5. Ç 5a, ºÃ½ À Ó, ² Ã;, É ÎßÌ. 5b Î Ë ÓÓ., À Î., A Ôº, σ Ô Ü Ë, n Ô Ë, R Ô, Q app Ô, T Ô Ëß. (1) Ì ln ε s = lna + nlnσ Q app /(RT) () ¼ (), Ë n É, ln ε s ½ lnσ» ; «Q app ËÉ, ln ε s ½ 1/T». ¼ Ë n Ä Q app Õ. 6 Ô ¼ Û Ù» ½ Ë ( 6a) Ä ( 6b) Ý. Ç Ë n Ä Å. ¹ [13,1], n=3, Ï ( Ï»Þ ) ; n= 6, Ï ; n >7, Ô (1). Ç, Q app 135 kj/mol (Mg Ä ), Ý Mg Ä ; Q app 80 kj/mol (Mg Ä ), Ý Ä. «Ö ËÉ, Ù Ë Àº.3.9,

1358 Þ Ü Ù Æ Five Power Law [15], ÔÝ Ï ; «² Ë, Ë º 7. «, Ç ÉÀ, 76.0 89. kj/mol, ºÃ Mg Ä (80 kj/mol), ÔÝ Ä., º Ð ( fcc, bcc Ä hcp Ó) À, Ï ½ Ä [15]. «½ Mg ln ( s, s -1 ). ln( s, s -1 ). -1-13 -1-15 -16-17 -18-19 -0-11 -1-13 -1-15 -16-17 -18-19 (a) 100 o C 15 o C 150 o C 175 o C.7.3 n=.5-8.0-7.8-7.6-7. -7. -7.0-6.8 ln (, MPa) (b) 76. Q app =86.7 kj/mol 77.9 85.6 89. 76.0.9 8. 8.1 7.8 15 MPa 0 MPa 5 MPa 30 MPa 35 MPa 0 MPa.1..3..5.6.7.8.9 1/T, 10-3 K -1 6 Ê Fig.6 Stress σ (a) and temperature T (b) dependences of steady state creep rate ε s 3.0 Ä, ß «Ö É (<0.5 T m ), Ä Ô Õ. Đ², ÕÌ µ ¹ Power Law Q app ½ Ð Ä [15]. Î [15 17] Î ÅР( Mg), Óº Ä. Ô, Àŵ Power Law Î, ½ Ä µ½ Æ, ÇÅ º Ä, «º Ä Ï Ä [18 0]. ̽. ÑÉ, µ ºÃ Mg Õ ¹, µ ßËŠε, Æ º ÐÅ µ. Î µî [8 10,1,1,] à Mg. Ç, µ ˼ µ, ÅÌ «, Ô Ë À 3.70 5.86, º Ä, ¹ËØ ¹ º Ý Ï. Æ µ Î Ü, É, Ï Ò. ØÉ, Ô µý Ë É ÓÔ Å «. Ð Æ ÆÎ Ï ( Ï Ï Ó) (Ï ± Ä) Ì ÎÓ µ Î, Langdon [3] É : ε s = ε g + ε gbs + ε diff(l) + ε diff(gb) + ε twin + (3), ε g Ï, ε gbs Ï, ε diff(l) Ä ε diff(gb) ÄÄ Ä, ε twin Î. ÔÉ Ï»Ä Mg À Ð Table Creep mechanisms of pure Mg reported in the previous investigations Temperature, Stress σ, MPa (Strain rate, s 1 ) n Q app, kj/mol Mechanism Ref. 150 50 0 50 5.86 106 1 [8] 197 17 ( 10 6 ).5 105 1 [9] 197 17 ( 10 6 ) 8 355.3 [9] 37 77 5. 135 1 [10] (>37) 77 >.5 6.0 10+95/σ [10] (>37) 77 <.5 1.0 139 3 [10] 17 517 <30 13.5+8.0/σ, [1] 17 517 >0 133.3.6σ 5 [1] 188 81 5.5 117 1 [1] 19 558.0 17 [1] 100 300 3.70.65 1 [] Note: 1 dislocation climb, cross slip, 3 Nabarro Herring diffusion, slip motion of dislocations on pyramidal slip system limited by nucleation of kink motion, 5 nonconservative motion of jogs on screw dislocations gliding in basal plane

Ù 11 ƱÄÑ : Á Mg Ô Đ 1359, Ô ÉÐ. º Û À, É²Ü Ù TEM Ä, Ï Ò., ËÙ Ì ¾ Î Ó Ì ( 5a), «Ó Ô± Ï, Á 7, ß Ï Å. Langdon [3,] ¹ ß, Ï Ò, «É ß, º ÎÀ. Bell Ä Langdon [5] ¹Î Mg 0.78Al Æ Ï, É 357 µm Ù 00, 0.7 MPa É Ï ÍÅ Í Æ 6%. Ƽ, µ Ù ß, É (ÔРĺ 1 h Ù ),. Á Ô½ ± Ï, Ô ÉÇ, ÀÅ, Ì ¹ÁØ «Ï, ² Ö, «É Í ß «Ö É. Ì ß Ì ÔÊ Î Ï, «Î Ï, Ò Ï ½µÒ. ±º Ä ² Ö ËÉÆ Î [15], É, (3) Ä ( ε diff(l) Ä ε diff(gb) ) Í µ. Ƽ, ËÙ Ì ¾ Î, ß Î ÃÖ Å. Ô Æº É Î º ε. Æ, É, Ý Ï Ï Ä Î, Ò ε s = ε g + ε gbs + ε twin () Ï Ä Ï Å Ø. «, Ù Ô, () Ö ßÎ, µ Í ß ½ Ë Ð É Ó «Å., ͵ ¹ º Ų ¾, µ¹å º Ù Ã. 7 ÎÆ Ò Fig.7 Schematic of cuneiform crack caused by grain sliding (1) É Õ µ Ö. Ó É, Û ÉÉ, «Ö; ÔÐËÆÎÎ ÉÇ, É ; º ˱º É, É ½Ó. () Û Ã Mg Ù «Ö Ë, Ë n À º.3.9, «² Ë, n >7; 76.0 89. kj/mol. ¼ Ý µ Ë ßÂÐ, Ë, Ý Ï ; «, Ô Ä. е Ð ßÎ ÝÂÐ º Ö. ÆÌ Ä, à Mg Ý Ï Ï Ð Î, Ï Ä Ï Åµ Ø. ¹º [1] Luo A A. Int Mater Rev, 00; 9: 13 [] Wang Q D, Zeng X Q, Lü Y Z, Ding W J. Mater Rev, 000; 1(3): 1 (¾, Á, Í,. ¹, 000; 1(3): 1) [3] Wang X Q, Li Q A, Zhang X Y. Light Metals, 007; 6: 5 (¾ ³, Ã, ÆÐ., 007; 6: 5) [] Zhang J, Pan F S, Li Z S. Foundry, 00; 53: 770 (Æ µ, Í, Ã. Ú, 00; 53: 770) [5] Mordike B L. Mater Sci Eng, 00; A3: 103 [6] Pekguleryuz M O, Kaya A A. Adv Eng Mater, 003; 1: 866 [7] Zhang X M, Peng Z K, Chen J M, Deng Y L. Chin J Nonferr Metals, 00; 1: 13 (Æ Þ, Đ,, Ô. Æ Þ, 00; 1: 13) [8] Shi L, Northwood D O. Acta Metall Mater, 199; : 871 [9] Jones R B, Harris J E. Joint Int Conf Creep, Part 3A, London: The Institution of Mechanical Engineers, 1963: 1 [10] Vagarali S S, Langdon T G. Acta Metall, 1981; 9: 1969 [11] Roberts S. Trans Am Inst Min Metall Eng, 1953; 197: 73 [1] Milička K, Čadek J, Ryš P. Acta Metall, 1970; 18: 1071 [13] Kim W J, Chung S W, Chung C S, Kum D. Acta Mater, 001; 9: 3337 [1] Chung S W, Watanabe H, Kim W J, Higashi K. Mater Trans JIM, 00; 5: 166 [15] Kassner M E, Pérez Prado M T. Fundamentals of Creep in Metals and Alloys. Oxford: Elsevier Ltd., 00: 1 [16] Sherby O D, Burke P M. Prog Mater Sci, 1968; 13: 33 [17] Sherby O D, Weertman J. Acta Metall, 1979; 7: 387 [18] Poirier J P. Acta Metall, 1978; 6: 69 [19] Nabarro F R N. Mater Sci Eng, 00; A387 389: 659 [0] Nabarro F R N. Acta Mater, 006; 5: 63 [1] Tegart W J. Acta Metall, 1961; 9: 61 [] Northwood D O, Daly K E, Smith I O. Mater Sci Eng, 1985; 7: 51 [3] Langdon T G. Philos Mag, 1970; (178): 689 [] Langdon T G. J Mater Sci, 006; 1: 597 [5] Bell R L, Langdon T G. J Mater Sci, 1967; : 313