ELECTRONIC STRUCTURE OF DIFFERENT REGIONS AND ANALYSIS OF STRESS CORROSION MECHANISM OF Al Zn Mg Cu ALLOYS

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1 Ý 45 Ë Ý 6 Vol.45 No Ý µ ACTA METALLURGICA SINICA Jun pp Al Zn Mg Cu Í ÅÛ¹ Ö¾ÜÄ ÔÌ Ê ß ÝÞ ÐĐ (Ý É, Ý ) Ø Ó Ð Ò Al Zn Mg Cu (7175 ) α Al, η Û α Al Ã,» ßà Zn, Mg, Cu H ÕÔ ½Ý³ Û ± ³ Fermi ³ ØĐ ½ ½, Õ Ö±. ½Ê : Mg, Cu H ¾. Mg H Ç ±, Î H, È ; Zn Ê ±ÕĐÍ, Ú ± ; Cu ³ Ê ± Fermi ³, Ú Ê ±ÕĐÍ, ÇÂ Ø ± Õ±. ½ÊÖ : η ÛÕ Fermi ³, ± Ì ±É Ò. ÀÅ η Û ß H, ÃÅ η Û Ò H Õ, ± ; Ù η Û Å ± Ñ, ±. ¼ Al Zn Mg Cu, Đ ½, Ö± Ú È TG111.1, TG Ð A Ù (2009) ELECTRONIC STRUCTURE OF DIFFERENT REGIONS AND ANALYSIS OF STRESS CORROSION MECHANISM OF Al Zn Mg Cu ALLOYS ZHANG Guoying, ZHANG Hui, FANG Geliang, YANG Lina College of Physics Science and Technology, Shenyang Normal University, Shenyang Correspondent: ZHANG Guoying, professor, Tel: (024) , Gyzhang1965@sina.com Supported by National Natural Science Foundation of China (No ), Science Research Program of Education Bureau of Liaoning Province (Nos.2007T165 and ) and Science and Technology Development Program of Shenyang (No ) Manuscript received , in revised form ABSTRACT The atomic cluster models of α Al, η phase and large angle grain boundary of α Al in Al Zn Mg Cu alloys have been constructed by computer program. The environment sensitive embedding energies of Zn, Mg, Cu and H atoms, interaction energies, Fermi energies and densities of state have been calculated by recursion method. The stress corrosion cracking behavior of Al Zn Mg Cu alloys has been analyzed according to the calculated electronic parameters. The results show that Mg, Zn and H atoms are easy to segregate on grain boundaries. Mg promotes the segregation of H on grain boundary, which leads to the embrittlement of grain boundary because of the attraction of Mg to H. Zn increases the difference of electrode potential between boundary and grain, which deteriorates the stress corrosion resistance of Al Zn Mg Cu alloys. Cu reduces the difference of Fermi energies between grain and grain boundary, and lowers the electrode potential difference between grain and grain boundary, which helps to slow up the corrosion process. The calculated results also indicate that the Fermi energy of η phase is the highest, so η phase will decompose firstly in the corrosion process as anode. Discontinuous distribution of η phase along grain boundary can weaken the segregation of H on the grain boundary because of the capture of η phase to H, and improve the stress corrosion resistance of Al Zn Mg Cu alloys, while the corrosion channel can form and speed up the corrosion process when η phase distributes continuously on the grain boundary. * É Ð , ß¼ ¹Î  ÐÐ 2007T , ¼ Þ Ð Ð Á : , º : ± : ÕÉ, ¾, 1965, ¹, ±

2 688 Æ Ý 45 Ë KEY WORDS Al Zn Mg Cu alloy, electronic structure, stress corrosion mechanism Al Zn Mg Cu Å ÈÃ Ö Ä Û Û Ü Ù Ð, Æ Ù ³Ö¾ ºĐ [1,2], º ÛÖ ² Æ [3,4] «Æ ÖÀ ÐÙ. à [3] Al Zn Mg Cu ÄÅ ( 7075 Å ) T6 Ç Ñ, ² ÈÃ Ö ¾ Æ; T73 ½ ², Ý Ä Ñµ 10% 15%; ÜÄ (retrogression and re aging, Ê RRA) ½ 7075 Å Èà T6 ÖÄ T73 Ö ². Ö Ò, µ ÕÀÙ ³ Ý ² Ö ¾Æ.» ÄÖ ² Í (SCC) [5] ³Ã É É Ü¾. [6] Ê, ÄÅ ² Ö² Ñ, ± Ò Ð Ó, ÓÇ ¾Ã ³¼Ö, Æ, ±Ò Ê, «; ÜÇ Ò, Æ, ÏÍ Ð Æ Ò. Ù«Ë Ä Í, ÖÐ, Ý Ã, ½Ð Ä Ê, Ù², ² Ñ Í Ò Í Ò, Å Í. É [7] Ê, ÄÅ H Ö µ Ø. H Mg Ö Æ, Å Æ Ö, Ð ² Û Ñ «. É ¾ Ö ÖÁÐ [8] Æ: ÐÉ, É ÐÐ ², ºĐÖ Æ µû, Ы. ÁÆ ² Í Ý Æ Ë, Å Ã ÊÅ, ¼½ à ÄÅ ² Í Èà ³. Al Zn Mg Cu Å ² ÃÆà Ò, ÆÆË ÍÒÖ ² [3,5], Ë ÒÍ Ö ÃÔà Ò. Ö Ú ÊÆºĐ Ò ĐÖĐÆ, à ¾,»ÇÞϳ ¾ Ø Ö², ÒлºĐ ÆÈà ³Ö [9]. ¼ Ñ ±Ó Al Zn Mg Cu α Al Ü η ÜÅ α Al Ä. Ä Zn, Mg, Cu H ÖÕÀ ¾ÞÃ Ü ² Fermi Ù ¾, ¹Æ ¾ Ö ² Æ, ½Ë ¾ Ð Al Zn Mg Cu ² Ö, ÊÜÐÍÒ Al Zn Mg Cu ² à ¹Æ. 1 À ÑÕÉÎ 1.1 Á Ò Al Zn Mg Cu ÄŠϳÏÞ Ç µ, Ð Æ Ö., ³ ÄÒÜÆ T Ü (Al 2 Mg 3 Zn 3 ), η Ü (MgZn 2 ) S Ü (Al 2 CuMg). É, ÄÅ H Mg Ö Æ, Å Æ, Ö ÐÉ ; η ÜÆ H Öµ Ø, Ã ÜµÛ Æ Ö H ½, Ö SCC. ÊÐ Ã Al Zn Mg Cu ÄÅ Ö ², Ñ ±Ó α Al Ü η Ü ¾. η ÜÊ ¾, P6 3 /mmc, Ê: a=0.522 nm, c=0.856 nm.  1a b Æ α Al η Ü «(Á Ì Zn, Ü Ì «Mg ). α Al ( 5324 ) η Ü Ä ( 4116, H Ê 4117 ) Ì Á «º Ô. α Al Ä ¼ Ñ ² α Al Ä (210) Ý, 001 Æ 36.9, Ð Ä Ö, ÔÐÐ AlΣ5 [001]/(210) ( Ê Ö Æ¾Æ Al Ö., Σ Ê ÐÛÐ«Ë ÐÛÖ«, «1/Σ Ê ÐÛ ) ¾ ( Ä 3778, H Ê 3779 ).  1c Ê α Al Ä (001) 1 Al Zn Mg Cu α Al Å, η Û Å AlΣ5 [001]/(210) ½ Fig.1 α Al cell (a), η phase (MgZn 2 ) cell (b) and AlΣ5 [001]/(210) grain boundary (c) appeared in Al Zn Mg Cu alloy (atomic numbers in clusters of α Al, η phase and boundary are 5324, 4116 and 3778, respectively)

3 Ý 6 ÔÈ : Al Zn Mg Cu ³ ÎÌ ¼ Õ 689 ÖÀ. 1.2 ËÏ Ashby [10] Ñ Ä: ½Þ Ê Ö Ã ºĐ Ò Ã ³². ¹, ÃÐ Ö Ò. ¾ Ö Æ, ³Ç Èà Æ. ½ ÊĐÆÖÞ Æ Â Ö, Zhou Ù [11] Đ Æ (DFT) Ö ³ (Cambridge Serial Total Energy Package, CASTEP) ÃÐ MgH 2 V Ö ÉÆ ; Ù [12] Ü Þ ÆÒ (discrete variational Xα method, DV Xα) Í ÃÐºĐ γ/γ Ü Ö ¾. ĐÆ ÖÞ ¹ Ç» Å, CASTEP ØÆ Ð Ö «º, Ë «ºÆРƵ, Ý ÐÚ µ Û. DV Xα Í, Í ³ ÆÖ. Æ Ö¾, Ð Ö Èú Æ, µè ÆÖ Ä µ Ë. Ä Ö Ð Æ, µ ³È ÆÅ ÄÖ Ã º. ¾ [13,14], Ê, ¼ Ä Ä [15] Ñ±Ó Hamilton ÄÛ, ÄÛÏÊ Ó ÆÒ Þ ( ÆÒ ), 1 ¼«(, E s Ê s ÆÒ, E p Ð E d Ê p Ð d ÆÒ ) [16]. ÁÆ Cu à p, à d, Ê, Cu ÖĐÊ d ÆÒ ( 1). Hamilton Ä ÛÏ ( Ö ) Ê Slater Koster [17], ¾ Ê [16] (h/2π) 2 V ll m = η ll m m e d 2 (1) (h/2π) 2 r 3/2 d V ldm = η ldm (2) m e d 7/2 V ddm = η ddm (h/2π) 2 r 3 d m e d 5 (3) Å, V ʵ ÆÒ Ü ² ( ¾ ); Ñ l, l «µ ÆÒ (s, p Ð d); Ñ m ÆÉÞ, m=0, ±1, ±2, σ, π, δ «; Ñ d «d ÆÒ; h Ê Planck ; m e Ê Þ; d Ê É ; r d Ê (Cu Ö r d Ê 0.67); η Ê ¾, η ll m 1 ÅÑ ³ [16] Table 1 Self energies of atomic orbital for the elements in the Al Zn Mg Cu alloy [16] (ev) Energy Al Zn Cu Mg H E s E p (or E d ) Ê: η ssσ =1.40, η spσ =1.84, η ppσ =3.24, η ppπ = 0.81, η sdσ = 3.16, η pdσ = 2.95, η pdπ =1.36, η ddσ = 16.2, η ddπ = 8.75, η ddδ =0.00. Ä Đ ßƲ Hamilton ÄÛ Ü Ú Ô Ò, n lo = 1 π Im u 1 0 E H u 0 (4), u 0 1 E H u 0 Ú «Å, Ü Ê 5. Im «, E Ê Þ, H Æ Hamilton, u 0 Ê Hamilton ÄÛ²Ü Ú ÖÂ, O «µ Ð. Ö¾ E st Ê E st = O l EF, E F Æ Fermi, N = lo EF En lo (E)dE (5) n lo (E)dE (6) Å, N ʾ ¼Ã Ó Ö, Ê: Al 3s 2 3p 1, Zn 4s 2, Mg 3s 2, Cu 4s 2 3d 9. 2 À Ã Õ Î 2.1  2a b Ê Å η Ü., Ú TDOS, ev -1 TDOS, ev (a) Free H Containing H E F = ev E, ev (b) E F = ev E, ev 2 η Û Fig.2 Total densities of state (TDOS) of grain boundary (a) and η phase (b) (E F Fermi level with free H)

4 690 Æ Ý 45 Ë Ð η ÜÏ H Ö, E F ÊË H Ö Fermi. Ë η ÜÖ ÌÊÒ, Ù Al, η Ü Ö Mg, Zn Å Ã s Ð p ÆÒ Ã À. Æ η ÜÖ, Æ Al ÖÅ Ê 3, Mg Zn ÖÅ ÙÆ Al, à 2 Å, ÞÐ Ä ÖÆ Ü. H Æ (H Ô ), Fermi µ (E F = ev), ÞÛÆ 20 ev Ö Ã,. H Æ η Ü Fermi ÃµÛ (E F = ev), º, Å ÞÐÇÆ Ã. Fermi Đ, Ù Ì H η ÜÖ Ò ÞÆ, η Ü ² Ö². 2.2 Æ ½ º ÕÀ ¾Þà E ese, ½ Đ ÃÐĐ Đ ÕÀÖ, Æ Ï³ Å. Æ ÅÃÐϳ, E ese «Ê [18] E ese = (E i ne self E i self) (E cl ne self ) (7) Æ ÎÅÃÐϳ, E ese Ê E ese = [E i (n 1)E self E i self] (E cl ne self ) (8) Å, n Æ Æ¾ ÖĐ, E i E cl Æ Ï µ ÏÃÐ Ö¾, E self E i self ÆĐ ÃÐ Ó Ö., E ese, ÃÐ ÈÕÀ, ¹ µ, à ÕÀ ¾Þà ÛÖÎ ÖÍ., E ese Û, ÃÐ ÈÕÀ, ÃÐ ÅÆÊ. ÔÄÖ E ese 2 ¼«. ½Ï Ä, Zn ² Ö E ese Ç, Zn ²., Zn Al Ã Ö [19], Zn Ë Al Ï Ù, ÛÏÑÜ «Ú. Mg Cu ÖÕÀ ¾Þà Zn ³ Ä Æ, Al Ö ³ Æ Zn, Å Mg Cu Ö E ese ºÛ,. Á ÐÖ ĐÞ : Æ Mg Cu ÏÍ [20]. Liu Ù [21] «Ö Ü ² ËÁ (ab initio DFT ³ ), ÃÐ Cu AlΣ5 Σ11 Ö Å Ê, Cu Å AlΣ5 Σ11 Ý «ÖÖÅ, 2 Ô Zn, Mg Cu ÕÔ ½Ý³ Table 2 Environment sensitive embedding energies E ese of Zn, Mg and Cu at different environments Environment Zn Mg Cu (ev) Grain boundary Grain interior µóæ ÎÖÎ. Liu Ù [22] ĐÆ ÖÞ, ÃÐ Mg Al Σ11 Ö Å, Mg ÓÆ Øº ±ÖÎ, ÅÁÆ Mg Ö Å, Al Ö¾ Ó., Ö ¾ËË ½ Å Á Ü, Ù : Ä Æ Ö. ÁÆ H Ö Áº, ½, ÕÀ ¾Þà ¼ Å (7). H Ï Mg µï Mg Ö E ese Ê ev; Ô² η ÜÖ E ese Ê ev. H ÃÐĐ Al, µ µ ÕÀ ÞĐ, Õ À ÞµÛ (E ese ʵĐ), Ù H ÐÅ Đ. º Ë ²ÖÕÀ ¾ÞÃ, H Ö ÞÛ, Å. º H Ï Mg µï Mg ÖÕÀ ¾ÞÃ, ½ÏÄ, Mg µû H ÖÕÀ ¾ÞÃ, H. Mg H Ë Ö Ë Ü ² [23] ÏÄ. Mg Ë H Ü ² Ê E = (E(M, Mg, H) + E(M)) (E(M, Mg) + E(M, H)) (9) Å, E(M, Mg, H) ÊĐ Mg H Ü Ä¾ ; E(M, Mg) Ð E(M, H) ÊĐ Ï Mg Ð H ľ ; E(M) ÊĐ Ä¾. Ö, Ü ² ʵ, «Mg Ë H Ü,, «ÝØÜ. ¹ÆÅ (9) Ö Mg Ë H Ü ² Ê ev, Mg H, Ê, Mg Ð H Ö. Malis Chaturvedi [24] Ã, Ï Ñ, ÏÖ Mg Æ Mg Ö 2 3 Þ, Mg ÏÃÉ Ð, Mg Ã Æ H Ö Å., þËË. ÊÅ, ÄÖ η Ü Èò H Ö², ÁÆ H η Ü ÖÕÀ ¾Þà Û, ² H Ö. 2.3 ƽ Ë ² Æ Ö Ò Í. µ Ö ÖÇ Ð¾ µ, ϳ ÖµÌ, µ ÐÖ Fermi, µ ÏÍÖ Î Ð Ò Fermi Ï Î Û, Û Fermi Ï Î, Öµ ÏÍ ±Ó Î. ² ² Ñ, ½ Fermi ϲÊ, Û Fermi Ï²Ê Ö² Í Ö Ð., ÏÒ² ÁÅ (6) Al Zn Mg Cu Ö Fermi Ê ev, η ÜÖ Fermi Ê ev. η ÜÖ ÎÛ, ² Í η Ü²Ê Ó.

5 Ý 6 ÔÈ : Al Zn Mg Cu ³ ÎÌ ¼ Õ 691 Ø η Ü«, ½ ² Æ, Æ η Ü²Ê H Ö Å ¼ (H η ÜÖÕÀ ¾Þ à Û, Ô²Ê ev, η ÜÊ ev), µû Æ Ö H ½, ÓÉ Ö ;, η Ü ÎºÛ, Ð ². Ø ÄºÌ ÖÚ η Ü, ² ² Ñ, η Ü ²Ê Ð ² Ò, ² Û. Á Ð Đ Ú Ü Ä, ² Æ, Í ÜÄ Ø «Ö Ä, Ö ² ƺ [25]. Ramgopal Ù [4] Ò Ú ÃÐ 7150 Å T6 T7 Ö² Ê, Ä T6 T7 η Ü S ÜÖ² Î Đ Û, Ê Ó., Fermi ÔÄÖ¾ Ë Ø Ö ¾Ë. Fermi» ²Ö, Ë ²Ö Î, Fermi Î. È Al Ë Ô Ö Fermi Ê ev, Ï Zn Fermi Ê ev, Ð ² Î, ² Ƶ Û. Cu Ë ² Fermi ( ev), µû Ë ²Ö Î, Èà ٠² ². Mg ² ÆÖ ËÝ «:, Mg ² Î (Fermi Ê ev), ÃÑ Æ ² ÆÖ ;, Á Ö ß, ÅÆ Ö Mg Ê H Ö Å. Liu Ù [26] Í Þ Ã, H µû Mg ÅÖ Ö¾, Ð ² «. Ê, Al Zn Mg Cu ² Í É ³², Ë Mg ² Ð µ. 3 ÃÎ (1) Mg, Cu H ÖÕÀ ¾Þà ºÛ,. (2) ϳ Zn Èà ² Î Ö², ² ¾Æ; Mg H à ², É Ð, ² Æѵ; Cu µû Ë ²Ö Ù ² Ö². Î, Èà (3) η ÜÖ Fermi, Î Û, ² Í ²Ê Ó. η Ü²Ê H Ö Å ¼, µû Æ Ö H ½, ÓÉ Ö ;, η Ü ÎºÛ, Ð ². Ø ÄºÌ ÖÚ η Ü, ² ² Ñ, η Ü²Ê Ð² Ò, ² Û.»Ç Ð [1] David A L, Ray M H. Light Met Age, 1991; 2(9): 11 [2] Wang H B, Huang J F, Yang B. Mater Rev, 2003; 17(9): 1 (Æ, Û,. ¹, 2003; 17(9): 1) [3] Ferrer C P, Koul M G, Connolly B J, Moran A L. Corrosion, 2003; 59: 520 [4] Ramgopal T, Gouma P L, Frankel G S. Corrosion, 2002; 58: 687 [5] Liu Y. J Beijing Union Univ(Nat Sci), 2006; 20(1): 31 (. Ø ( ), 2006; 20(1): 31) [6] Lü H. PhD Thesis, University of Science and Technology Beijing, 1998 (. ± ÍÆ, 1998) [7] Huang X Y, Li Y H, Xiao J M. J Chin Soc Corros Prot, 1984; 4(1): 42 (ÛÕ,,. ɱ Ê, 1984; 4(1): 42) [8] Najjar D, Magnin T, Waner T J. Mater Sci Eng, 1997, A238: 293 [9] Xiao S X, Wang C Y, Chen T L. The Application of the Discrete Variational Method in the Density Functional Theory to Chemistry and Materials Physics. Beijing: Science Press, 1998: 92 ( ß, ÆÀÇ,. ÆÕ Õ Ñ ¹ Õ. : à Û, 1998: 92 ) [10] Ashby M F. Philos Trans R Soc London, 1987; 393A: 322 [11] Zhou D W, Peng P, Liu J S. Sci China, 2006; 49E: 129 [12] Peng P, Han S C, Zheng C X, Liu R S, Jin T, Hu Z Q. Rear Met Mater Eng, 2005; 34: 854 (, ÎÚ, Ý», ²,, µ.  ¹ Ê, 2005; 34: 854) [13] Liu G L. Acta Phys Sin, 2006, 55: 1983 ( ÇÒ., 2006; 55: 1983) [14] Liu G L, Li R D. Acta Phys Sin, 2006; 55: 776 ( ÇÒ, Ó., 2006; 55: 776) [15] Haydock R. Solid State Physics. Vol.35, New York: Academic Press, 1980: 216 [16] Harrison W A. Electronic Structure and the Properties of Solids. San Francisco: Freeman, 1980: 551 [17] Slater J C, Koster G F. Phys Rev, 1954; 94: 1498 [18] Wang L G, Wang C Y. Mater Sci Eng, 1997; A : 52 [19] Gruhl W. Aluminum, 1978; 54: 323 [20] Fan X G, Jiang D M, Shan C Z. Light Alloys Process Technol, 2006; 34(2): 31 (, ³,. Ç, 2006; 34(2): 31) [21] Liu X Y, Xu W, Foiles S M, Adams J B. Appl Phys Lett, 1998; 72: 1578 [22] Liu X G, Wang X W, Wang J Y, Zhang H Y. J Phys: Condens Matter, 2005; 17: 4301 [23] Hu Q M, Xu D S, Li D. Acta Metall Sin, 2002; 38(Suppl. 1): 562 ( Æ,,., 2002; 38( Î 1): 562) [24] Malis T, Chaturvedi M C. J Mater Sci, 1982; 17: 1479 [25] Zeng Y, Yin Z M, Pan Q L. J Cent South Univ Technol, 2002; 33: 592 (Ð È,, Æ., 2002; 33: 592) [26] Liu X G, Wang X W, Wang J Y, Zhang H Y. J Mater Sci Technol, 2006; 22: 135