49 Ö 6 Đ Vol.49 No ACTA METALLURGICA SINICA Jun pp

49 Ö 6 Đ Vol.49 No.6 2013 6 667 674 ACTA METALLURGICA SINICA Jun. 2013 pp.667 674 Al Â Ã Ì È¼ Ú Ñ Ê 1) 1,2) 1) «3) 3) Æ 3) 4) 1) ÑÞ Ü ËÍ, 212013 2) ÑÞ ³ßË, 212013 3) ÑÞ ÆËÍ, 212013 4) Þ ÆËÍ, 211189 Đ Ü ³Ì Al(α Al) ß Al Cu Mg ÙĐ Ï 2A02 ² Å ÀÐ, ÊÅ TEM Õ Å «Ú Ü ½ ²ÅÆÁÔ«. ÅÔ Ì, 2 Đ ±«ÅÆÁÔ ¾. α Al ² ÅÆ ÜÞ ½ Ú ËÐ. Ö² ÒË, É Ú, Ú Å ³, Ú ß ºÎ Ú ß Ú Å, Đ Bauschinger Á (BE) ß º µë Ó. Ï 2A02 «² ÅÆ ÜÞ Å, ½ «Å ß º «Í ³µËÅ Ú«² Ä «ÛÖ, º «ÚËÐÆ ÎÉ «Â Ú. Ö² ÒË, ËÅ«Ã Ä Î ; ÚËÐßĐ À É»Ð Ú ÈÅ (GNBs), É«Ô È Ï ºÆÖ Áº. Â Ú ßÚØ ß ÁÆ ³ É Ï ±² Å «ÅÆ. Î Ì Al(α Al), Ï, ², Å, Ú, Å Á TG115 ÓÖ» A Ó ºÁ 0412 1961(2013)06 0667 08 DISLOCATION MECHANISM OF SURFACE MODIFICA- TION FOR COMMERCIAL PURITY ALUMINUM AND ALUMINUM ALLOY BY LASER SHOCK PROCESSING LUO Xinmin 1), CHEN Kangmin 1,2), ZHANG Jingwen 1), LU Jinzhong 3), REN Xudong 3), LUO Kaiyu 3), ZHANG Yongkang 4) 1) School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 2) Analysis and Test Center, Jiangsu University, Zhenjiang 212013 3) School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013 4) School of Mechanical Engineering, Southeast University, Nanjing 211189 Correspondent: LUO Xinmin, professor, Tel: (0511)88780832, E-mail: luoxm@mail.ujs.edu.cn Supported by National Natural Science Foundation of China (Nos.51275220, 51105179 and 50905080) Manuscript received 2013 01 24, in revised form 2013 04 02 ABSTRACT Surface modification experiment of the commercial purity aluminum (α Al) and Al Cu Mg alloyed aviation aluminum alloy 2A02 by laser shock processing (LSP) was implemented. The surface strengthening effect of both the target materials was investigated from dislocation mechanisms of microstructural response by means of TEM method. The results show that the strengthening effect of the two kinds of materials by laser shock processed is significantly different. The strengthening mechanism of α Al by laser shock can be attributed to the multiplication of a large number of dislocations. With the increase of the impact number of laser shock and the degree of deformation, the new generated dislocations will pile up and interact with the forest dislocations, and the dislocation lines will gradually evolve into waved like, or wind into dislocation tangles and dislocation networks. * Ò Ý Ï 51275220, 51105179 ß 50905080 Å Ï Á : 2013 01 24, Ï Á : 2013 04 02 Ì : ÉÊ,, 1951, DOI: 10.3724/SP.J.1037.2013.00035

668 Í 49 Ö But the hardness curve of the laser shocked (α Al) will fast and linearly decline due to Bauschinger effect (BE) and stress wave damping. The laser shock strengthening mechanisms of the aging hardened aluminum alloy 2A02 can be summarized to the enhancement of the matching between the elastic energy of dislocations with the ultra high energy of laser shock processing due to the higher matrix strength and the dislocation pinning effect of large number of dispersed precipitates, as well as the complex dislocation networks in between the precipitates constructed by the dislocations induced by laser shock. The matrix strengthened by laser shock processing and the precipitates keep the extra semi coherent relationship to coordinate the total deformation, with the number of laser shock increase, dislocation multiplication and the vacancy motion constitutes geometrically necessary boundaries (GNBs), which consists of the sub grain boundaries to refine the matrix into the nanometer grains. The strengthening mechanism of surface modification of aluminum alloy by laser shock processing is formed of the internal stress state caused by the combination of the complex dislocation configurations and the Hall Petch effect of the nanocrystalline grains. KEY WORDS commercial purity aluminum (α Al), aluminum alloy, laser shock processing, surface modification, dislocation, microstructure ³ «Ë Ð Ô Ï ²±Æ ½, Ý À ²±Æ, Ã ²±Æ Ò, Ú«¼ Ý Ï, Ö ÙÃ¹ Î [1 4]. Û À Á Ë Õ Ï Þ, ³³» Æ Û µëø ²Ï «Ý [5]. ÇÔ ¹ÅÀÒ (GPa TPa) Å Ô (¼ È) ÅÀ (10 7 10 8 s 1 ) ³ ¼, ÈÓ Û À ÌÑ ÒÆÆ, ¾ Æ Ç Ê Ã ÍÏ ²³ Ï «Ï [6 8]. Ó, ÈÓ³ Í±, ±Æ «ÏËÇ ¼ «³» Æ»¼Ç ²±ÆÛÈÊ Ï Ï, ¹ ±Æ, Ï «Ï, ¾À¼, «± Ç± Æ [9]. Ñ, ¾ «ÜÁ, Î ±Æ Ó³, Ê Æ ¾ ¹ Æ «±, Ó Ï Ê Æ «± [10], ²Æ Æ Ä Ê «ÂÕ., ³ ÍÏÆ ²Ç«µ ¼ ³ Ï «Ï, ½ Ï Ï¹Û ² µ «[11]. Ë, ¾³ ±Æ ÏÐ«ÂÕ ¹, Ð Û É µ Æ Æ ³ Ø. «¼ÆË Á ¾, Â ¹ É Î ± Æ Ç Ð Á Ï; º«¼ Æ, ¾ ² ß Ä Æ Æ Đ Æ ÃÊ ² ÍÏ ÂÕ. Ñ, Í± ² Í Ð Al Øµ Al Cu Mg ¹ 2A02 Ú ± Á ² ³ ±Æ«Á, Ë«Å (TEM) µ ¾ ÇÏ «ÏÐ Æ Û Ý, ÍÏ Æ ³ Á ³ Ç ² ³. 1 Û Á ² ² Ð Al( ¼ È α Al) Al Cu Mg ¹ Â Í2A02 Ú ( ¼ È2A02 ). α Al Ð Ý 99.999% ÀÐ Al, Ð Cu+Si+Fe+Ti+Zn+Ga Ø (Þ )<0.01%. α Al Æ, µ Ã²Æ, ¾± Ø ³ Æ. 2A02 ÐÊ (Þ, %) : Cu 2.6 3.0, Si 0.30, Mg 2.0 2.4, Mn 0.4 0.7, Ti<0.15, Al. ³ Î Ø 40 mm 20 mm 2 mm, Á ½ α Al Î Ç 350 2 h; 2A02 Ç 500 Ç 170 Â 16 h. Á Í±Ç Gaia R Nb:YAG ÀÏ ³ ¹ ¾, ³ Á Ú² 1 ÛÇ. Û ³ 10 J, ³»Ã 1064 nm, 10 ns, «6 mm, Þ 5 Hz [12], ² 2 ÛÇ. Ç³, Î ±Æ Ó MIC Ð 1 ² Æ «Fig.1 Schematic of laser shock processing

6 Đ ÈÉ : Al Þ ĐÎ± Ä Å Ù Û 669 30 28 (a) 26 Hardness, HV 24 22 20 18 16 0 50 100 150 200 250 300 Depth, m Ð 2 ² ÅÆ Å «½ Ò Fig.2 Schematic of laser shock processing scheme (a) and the distribution of different repeated rate in a spot (b) À 0.1 mm Al ¼ ± Æ, ¼ ±. «³ Ã Æ,»» ß±Æ. HVS 1000 Í Æ Î «±ÆÜ ¼. JEM 2100 À Å (HRTEM) ³ Î Æ µ, ³ HRTEM Inverse Fast Fourier Transform(IFFT) µ Û. Î ½ Â Ê Î, Ö «, Å, Ø ¼¹Ý Ê. 2 Û ÀÐ Ô 2.1 Í ÉÅ ½ ß 3 ³ α Al 2A02 ±Æ. ß, ³ ³¾¾ ±Æ «±. À ²Ý 58% 55%, Ò, α Al Ô Í ¾ 2A02. Ë ¾ Þ Ý¾ ÛÙ. ¾³ ±Æ ÓÏ Ï, Û ß ½ ² ÛÙ Bauschinger Â (BE) ¹ [13]. ² 2b ÛÇ, Ç«Ç «4 Ó. ß Ó³ ½ Ä, ¾³ Â, À, ¾ÇÄ Å Ä. Ñ, ÈÓ BE, ¹À Ã ( «) Ì, ¾± ±Æ Ì. Å, Ù BE Ò¼ [13]. BE ² ²Ð Û Á Û ¹, ¹. Ç α Al Ð, ß Å Õ I Â, Ç Ð, ¾ Û «À«Â [14]. Ó, Ç³ Å Hardness, HV 90 85 80 75 70 65 60 55 (b) 50 0 200 400 600 800 1000 Depth, m Ð 3 ² ÅÆ α Al ß 2A02 Ï Å Û» «Fig.3 Hardness distributions along the laser shocked surface of α Al (a) and aluminum alloy 2A02 (b) ÅÀ ÄÝ ¼, ²» ¹, µ ËÇÑ Ä. α Al Ï (α Al 70 GPa, 72 GPa), ², Õ Û, Ç Ä ÏÐ Ñ Ü»Ð, ± Ã» ¹Õ,, Û α Al Ð¾ Ï «Â. Ç 2A02 Ð, «ÀÀ, ²Ç Ó Ð¾ Å Õ I Â, Æ ¾µ Ç ³ ÅÀ ÅÀ, Û ³ Á Ü Ã Ûß É «Â, Û α Al Ê Æ, ³ ±ÆÀ ßÝ 650 µm ¾. 2.2 Í É α Al ½ ß Ò Ë 4 ÛÇ Ç α Al ³. ß, À, Û Ç É, ² 4a ÛÇ; 4b ÛÇ Ã Ç ¾ Ð ½ Ï Û Ï, Ñ Ã ± Û Ì ¼ Û [15,16]. Û Ð Al, Õ Û.

U i 670 wo α Al }' h ^ / w!,. 5a wo ~o^ a e H }k p' jr w. ju ` woi }: H5, % 4 KW Y ; s' h ^ o dt7, w,,$, R wa6 - w,e %(. m, α Al }> so" w ( 4), R w-{g s`k+ w3 f Hn, r* w! T4 / WR w? wgn, & 5b d wo. _ α Al O\.>'h^ G, WR w,$,rt w6 s w E %(S%N$"mp H. 5 49 r +m{=, O'h^ /.>%(0, α Al e7 N > w Tm w. W M T I g!, R T w : b (Peierles Nabarro) + w 6aQE % ( Æ. w Tm w. i α Al \'h^ >%( G, { ~ G9 e w s q w I }sp" v : v = d( x) dt M}, t G9; x 'h^ G w 8 Oa e l 4 &g α Al TEM Fig.4 TEM images of grains (a) and hexagonal dislocation networks in a grain (b) of α Al before laser shock processing l (1) &g v { { 5 α Al Fig.5 TEM images of evolution of dislocation configurations of α Al laser shocked (a) straight and flat dislocation lines, single shocked (b) pile up and zigzag, twice shocked (c) dislocation networks, triple shocked (d) dislocation tangles, fourfold shocked

6 <PQ : j Al z5 V%f\ #LBZ u w 671 ". 2 O, "6 wk":b. * wk"t \W G>L!j} aq w2 5O, pgs E 7, wi } sp " v A0C. '2 Burgers J! }:W Gw:, k 6 x w,e %( X_a, O ' h ^ 9 > 0, ' h ^ *n*wrgn, _a W WRHK" K" / w K" ρ 6 9 ε b- :. * 2A02 7 X t -!) b :, a \ ' h ^ Ig!%(G, +2`KH/54)b: V ε (2) ρ =k b v %(, w Tm % 4 O ) b : h9 w? ( M}, b Burgers J!W, v w I p ", k 6 ^ 6b). P o w 8 Z ;, O' h ^ o, o d :b - d. N 5 }wo w Tm 4D, A w 8 :k u # K ", r * K e T7, ' h ^ M (1) (2) - {f, +2 ε b S, r * g!j 4. ' h ^ / w Tm 6 w I p " v ^ 2.4 n9~q5s;wn =`L[gOuy;zt 7 ' h ^ 2A02 7 X HREM A. r o d :b. O' h ^ Cb > 0, v As ^ o dt 7 * C. +2 α Al e " H, 1Y B }/ }{ ki C ' h ^ w a L ", {= ) b:6 W E, `3 S+2)b: w, s w,$ wgn #'^ g! " E P R y E h9 q g 2, r *, ' I g! +X*K // ^ g! <', $" 8 p (J9 2, r }K* F! al" O" 0C. {f' h ^ g! Ex 2 W. 2.3 n9~\y;wn )b:6 W 2 ug, -!y 6 wo ' h ^ / w O, ^aq g 5 M W. + 8 {=, ) b : 6 h9 4W. '2(a α Al j, woaqgk"hh, s WW"T7*Ca e W, *T7K"H ( 6a). wtm Æ[L (extra semi coherent) b- ` % U α Al O\ ) Cb ' h ^ W s W }, a 9T": d C2S -{g, _d d 8 "2{gz. `, Ov^aQg+2\ a d C G Æ Y 8 aq " >, u w! Tm, *ae Æ RH5.., Al BwgH, q m m [17] l6 { 6 W`Pf&g. v > α Al 2A02 TEM Fig.6 TEM images of the dislocation networks at grain boundary in α Al (a) and aluminum alloy 2A02 (b), induced by laser shock processing l 7 &g 2A02 6 W (a95 { IFFT HREM Fig.7 HREM image of a precipitated particle and the matrix (a) and IFFT image shown the dislocation configurations (b) in aluminum alloy 2A02 laser shocked

672 Í 49 Ö ÐÆ. «, ÇÜ «Ç¼ Ï Õ (Portevin Le Chatelier, P LC) [18,19], ³ Å ÅÀ Ã ± P LC Â. Æ α Al ¾ Ë Ð Ä ¾Å± ÃÏ, ± Ã Ï. 8 ß µ Ï Ï. ÈÓ ÐÛÇ Æ Õ, µ Ç 10.7% Û, Ç³ Æ Ä ¹. ³, Ô Çµ «Û ÏÅ Å ¹ ¹.» ß Õ±, Çµ ÌÑ ÛÂ Ï, Û Û, Ù 1 1., Æ Ä ¹ µ Ç³ «Ç «Û ÌÑ Æ Ä ¹. ³ Ç Ð» À ÛÛÙ Ä «Æ Ä ¹ À ¹Æ, Ö Ð ²±Æ «Â. Ð 8 2A02 Ï ««IFFT Fig.8 IFFT image of the metallurgical relationship between a precipitate and the matrix of aluminum alloy 2A02 2.5 2A02 Ä Ç Ò Ë ¹Ø ±Í, ±Æ«µÕ Ï» Â [20]. Ç Á Ð, ³ α Al Ð ¹ Â, ß Û ÃÏÁ Û ÆÜ» ¹ ; Ç ³ ¼, Ç 2A02 Ð Â. 9 ÛÇ 2A02 Ð Â Ï Þ. ß Ç 100 nm ¼, Þ Ì, ±Í³ ÏÊ Ê Ô¹ Ð ¹. 10 ÛÇ ³ ÏÊ Â ÛÁ Û ±. ² ÛÇ, ³» Û Ç Û Ï Û Å, Ê À Û ²Ç«µ ÅÀ ¼Đ¹ ÛÉÆ ¼ ÛÉÆ (geometrically necessary boundaries, GNBs) [21]. ÃÔ¹ Â Ï Û ÉÆÏÊÕ É, ½ α Õ, ² 10a ÛÇ. Û Â ÊÆ ¾ Õ É Û Ê É ÏÍ¹Û¾, Ð ¹Ê Ã, Ê ²Ç³ «±Æ À, ¾ Ú«Ç. ²Õ Ö É, Û ÏÊ É β 30 40 [22], ² 10b Û Ç. Í ³ ßÇ ²±Æ Ô¹ É Â. ³ Â Ú, Ø Û À, Ð ß À. Al «µõ Ï Í Ó ÀÝ 10 4[23,24], ±ÍÇ É ¹ Ý ¾ Â ÊÔ³, Ç³ Å Ï Å À ¼¾ ÛÏÅÐ Ï, É À, Ù ÏÊ [25]. Ç, ß Ë ²Ç «Ó ½Ç É, Ç ÏÐ,. Ç ± ¼, Ð 9 2A02 Ï² «Á «TEM Ý «Fig.9 TEM image of nanocrystalline grains of laser shocked aluminum alloy 2A02 (a) and corresponding electron diffraction pattern (b)

<PQ : j Al z5 V%f\ #LBZ u w 6 l &g. v4æ` 673 10 IFFT Fig.10 IFFT images of sub grain boundary constitution by dislocation wall induced by laser shock processing (LSP) (a) GNBs (b) sub grains at nanometer level with high angle grain boundaries l &g. vh ^I`V QrV { 11 IFFT TEM Fig.11 IFFT images (a e) and TEM image (f) of effect of dislocation movement induced by LSP on the nano microstructure evolution process of aluminum alloy 2A02 (a) original crystal (b) dislocations induced (c) dislocation multiplication (d) GNBs (e) sub grains (f) nano crystallization N 2w-> -{ g,, * 2 S A ~ O w [S> p'n 2 7 5 > = 6, r*kp-5ja Wg wq N WR, R#' h^ _J!y. 11 wo 7 X' h ^ _J a s W } w I w % (. +2 Oh e ' h ^ ( \, s^ odt7, wk"a2%t7, & 11a c wo. a y 6", 6 W Cb; T, s! 5 /Oa e w, 7 5 R a e Cb 0 0 ~ > W R p- 5J a Wg w Q N (GNBs), = 11d; ` 5J " ~A W R G _J a, & 11e; wo ' h ^ _J a WB. _J a aq % N6 $ C 150 m2/cm3[26], aqwx, Po Hall Petch YM, `R 7 X' h ^ Jq B α Al 0 >. 11f 3 Xa h^ 7 %N "5& H %N " 7 X, $ B < "R, + Æf<p "R. (2) α Al ' h ^ % N $ " H O2' h ^ MH 9 / w Tm. +2 $"H ' (1) ' K α Al 2A02 X $ 58% 55%, α Al $ 2 2A02

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