EFFECT OF WELDING PROCESSING PARAMETERS ON POROSITY FORMATION OF MILD STEEL TREATED BY CO 2 LASER DEEP PENETRATION WELDING

49» 2 «Vol.49 No.2 2013 Ý 2 181 186 Ï ACTA METALLURGICA SINICA Feb. 2013 pp.181 186 Åà ÎCO 2 Þ ÛÑ Á Æ ³± ( ÊÀ¹ ÀÀÀ, Ê 130022) ÒÝ Å± ¾, Ô±¼ CO 2 Â, Đ Â Ó Ù É, ¼Â Å, ű˻»Â Æ Ð É «¼ Ò º ¹ ÒÝ Â Ñ º. Õ, ÒÝ CO 2»»Â, Ë Û ÜÖ Ô º,» Å» ÒÛ» ß. Ñ Ð É Ý, ɲ ÝÏĐ, É 35 L/min É ; Ñ «Ý, ɲ ÝÏĐ Æ, Æ», «22.5 Æ É. ¼ 4 kw É, 0.75 m/min Ò ÆÄ. À,»Â, ÒÝ, º ¹ ÈÌÓ TG456.7 Å Ú A Å 0412 1961(2013)02 0181 06 EFFECT OF WELDING PROCESSING PARAMETERS ON POROSITY FORMATION OF MILD STEEL TREATED BY CO 2 LASER DEEP PENETRATION WELDING CHEN Gao, GAO Ziying College of Science, Changchun University of Science and Technology, Changchun 130022 Correspondent: CHEN Gao, associate professor, Tel: (0431)85582291, E-mail: chengao@cust.edu.cn Manuscript received 2012 10 08, in revised form 2012 11 12 ABSTRACT The porosity in the welded seam can be generated easily during the CO 2 lasernonpenetration deep welding of low carbon steel, which affects the quality of welding. This research uses the mild steel as the object for the high quality requirements of welding. The advanced high power CO 2 laser generator was used for the welding experiment. The method of cutting cross section of weld seam was used to analyze the porosity number and observe the morphology and location of porosity in the weld. The effects of such process parameters as shielding gas flow, laser beam inclination, laser power and welding speed on porosity generating were discussed. The research results show that the generating of porosity is due to the unstable collapse of the keyhole in the process of CO 2 laser nonpenetration welding of low carbon steel. The porosity would be formed when the speed of bubble escaping form the weld pool is lower than the speed of melting metal solidifying. The results also show that with the increase of shielding gas flow, the porosity number presents a curve of increase firstly and then decrease. The lowest porosity number can be obtained at a 35 L/min of gas flow. With the increase of laser beam inclination angle, the porosity number shows a trend of decrease after increase. Under the condition of deeper penetration welding, the relatively lower porosity number can be obtained at the inclination angle of 22.5. When the laser power is 4 kw, the porosity number is lowest. At the condition of lower welding speed, the bubble can escape easily for the longer existence period of melting weld pool. * Ëij : 2012 10 08, Ë ³ : 2012 11 12 ±, Ð, 1971 Þ, Í : DOI: 10.3724/SP.J.1037.2012.00574

182 49» Thus lower porosity number and porosity number can be achieved. The porosity can be inhibited effectively at a welding speed of 0.75 m/min. KEY WORDS porosity, deep penetration welding, mild steel, processing parameter ÓÞ ØÜ ÙÖÇ Þ» ÜÓ Ü,» Õ. À³ÓÞ Ù Æ Ã ÙÈ, Ò Ð Ã Ø Û Æ²ß Õ [1 7], ÓÞ Ð Ã Î ÌÅÓ. È ÓÞ Î ¼Ã, ÆÈ ¼ÅÐ Ã, à ¾. Èà à ²µ, ÊÆ Ù Ò». Ʋ [8 11] Ö, Рû º Ù Ò», Ʋ Ñ ÆÌ» Ö ß ÃÐ Û Ð. Î Ð Ã ÁÓ Ì Æ². Á Ú Ã µí ÕÀ ßÉ [12] Ó ÝÛ [13] Ð. Ù ÃÕÚËÅ ¼¹ ÂĐ [14], Ð Ã [15,16], Û Ð Ã ß [17 19] Ó Ã º [20] Ð. Ý, ÅÞÌû.» ÓÞ Æ², Ʋû º Ó Þ ¼Å Ð ¼Ã Ò», ß Á, Î ÓÞ Ð ¼Ã, à ²µ, Å Ã Ê, Ð ¼Ã ÓÞ Ã Õ ¾º. 1 Ð ÉÇ ÀÉµÍ Õ 20 g ÓÞ, Æ Â ( Ê, %) : C 0.20,Si0.15 0.30,Mn0.50 0.90, P 0.035, S 0.035, Fe ÝÊ. à ÊÊÁ 80 mm 30 mm 12 mm. 1 ÕÅ Ð Ã ÀÉ Å. Ð, α û, α Ð ß» ½Ü, à ½ ÕÅ. 1  ÈÄ Fig.1 Schematic illustration of laser welding test Ð Õ DC050 CO 2 Ð, ÏÆÐ Ã. Õ Ü» ½Ü» Ù Ð Ã ÀÉ. Ã Õ µ, Õ He Æ Ar Ç, He Ar=1 2. ½ ÕȲ : Ø ²ÈÇà ½ Æ, Õ 3% ½, Õ Ã± ½ Ú, ² ÕÜ ½Ã Ô ±Óà ; Ø ²È Ã Ê Ô Æ, Õ 5%, Õ Ã± ½ Ú, ² ÕÜ ½Ã Ê Ô ±ÓÃ Ê Ô.» ÕØ ² Ú 5 mm à ÛÐ 0.25 mm 20 µê Ô Æ ¾¼, Ú ÜÐÜ 0.05 mm Ê. 2 Ð Ë«2.1 Ü ÖÕÆÜÒ Â Ð ½ P=4.5 kw, à V=1.75 m/min, Ð α=22.5, Ê f=+2 mm, Ê ÊÆà ¼ Ò» 2 ÕÅ. Æ, ÊÎ 15 L/min ÅÞ 20 L/min, Ê Ó. ÊÎ 20 L/min ÅÞ 25 L/min, ʱ¹ÅÞ. Ò Ê 25 L/min, Ê Â. Ê ÅÞ 35 L/min, Ê. ¼ Ò Ê ÅÞ ³Æ Þ Ç. Ê 30 L/min, ¼ Ù Ç. 2.2 ĐÝ Æ Õ P=4.5 kw, V=1.75 m/min, f=+2 mm, Ê L=20 L/min, Ð ÊÆà ¼ Ò» 3 ÕÅ. Æ, Ð 32 28 24 20 6.7 16 6.6 12 6.5 15 20 25 30 35 Gas flow, L/min 2 Ð É Å» Ѻ Fig.2 Effects of gas flow on the porosity number and penetration depth 7.1 7.0 6.9 6.8

2 «: Á ¹ ÑÜ CO 2 ºÁ й 183 Î 0 ÅÞ 7.5, ÊÅÞ, ÎÐ 7.5 ¼, Ð Î 7.5 ÅÞ 37.5, Ê Ç, 30. Ò Ð Î 0 Å 37.5, à ¼ ÅÞ Ç, Ð 15 ¼, Ò Ð Û Å ±¹ Ó. ¼, 22.5 Ê. 2.3 ØÆÜÒ Â V=1.75 m/min, α=22.5, f=+2 mm, L= 20 L/min, à ½ ÊÆà ¼ Ò» 4 ÕÅ. Æ, Ð ½ Î 3 kw 4 kw, ʱ¹. Ð ½ Û ÅÞ, ÊÚ Â Å. Ò Ð ½, à ¼ ÅÞ. 2.4 ØÆÜÒ Â P=4.5 kw, α=22.5, f=+2 mm, L= 20 L/min, à ÊÆà ¼ Ò» 5 ÕÅ. Æ, à Π0.75 m/min ÅÞ 2.75 m/min, Ã Ê ³ ÅÞ Ç, à 1.75 m/min, Ê 40 7.8 35 7.6 30 7.4 25 7.2 7.0 20 6.8 15 6.6 10 20 18 16 14 12 10 5 6.2-5 0 5 10 15 20 25 30 35 40 Laser beam inclination, deg 3 «Å» Ѻ Fig.3 Effects of laser beam inclination on the porosity number and penetration depth 6.4 5.4 8 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Laser power, kw 4 ¼ Å» Ѻ Fig.4 Effects of laser power on the porosity number and penetration depth 7.0 6.8 6.6 6.4 6.2 6.0 5.8 5.6. Üà ¼, Ã Ü 1.75 m/min Ó, à à ¼ Ò», à 1.75 m/min, ¼ ±¹ Ó. 3 Ë«Ù 3.1 Ä Ï Êß ÜÒ Ô Ð ¼Ã, ² ½ Ò Ð, µí Å. ÛÂ Ì µíæ Å ², ¼¹, Ú µí. ßÆ ¾ ÔÆÅß ÛÆ ÄÅ ßÚ Ì., µí Æ ß, Ò ß, ±ÈÜ ß Ý¾Ú. 6 20 g Ð ¼Ã Ã Õ ½ Ô., Ã Õ Ã ß Ã È, «¾, ÐÙ Ý, Ö Ã, ß²«Ý, Õ Åß ºÎ. 6 Đ ÓÆ Æ Ã Î Ð Ó Õ. µ, ³ÙÈ. ßÐ Ð, Î Å, ¼¹ ßÄÁ Å µù. Ò ¼, µ, Ü Æµ. ß Û ÙÒ, Õ Ý Ü 14 12 10 8 6 4.4 0.5 1.0 1.5 2.0 2.5 3.0 Welding speed, m/min 5  ޻ Ѻ Fig.5 Effects of welding speed on the porosity number and penetration depth 6  Գ ¼ Ó Fig.6 Vertical section of a welded seam 5.4 5.2 5.0 4.8 4.6

184 49» Ù ½Ý Õ. Ì Ã P abl +P g = P h +P σ (1) Ã, P abl ÃÄÅ, P g Ê ÄÅ, P h ÄÅ, P σ ÔÆÅ. Å Ð Ì 7 ÕÅ. Ð ½ Ò «Å Å, ß ½ Gauss ±, Ù Ò «Û Å ½ ² Ü Æ, Á Ì ÜÊ Æ ÄÅ. ÄÅÆ ÔÆÅ Ù½Ý «Ì. ÔÆÅß ÄÅ Ì Á Ì ÓÓ Æ. Ð ¼Ã, Ó, Ý µ¾ Ó, [21,22]. Ü Ú, Ì. ÓÞ Ð ¼Ã, ÝÛ ¼À¼. ¼¹Ã Æ. 8 ÆÌ 20 g CO 2 Ð ¼ÅÃ Ã Ê ÔÓ. Æ, ÈÐ ± à Õ, Æ ¾Ù Ï, ÀÌ Ï. Æ ¼À ܼÀ. 3.2 ÔÍ He Æ Ar Ç µ Ð Ã. Ê 15 20 L/min, Ü Æ¼À Õ ² Ý ¾Ú, Ê ; Ò ÊÅÞ 25 L/min, ÊÅÞ. Ð È ÊÅÞ, à ¼ÀÕÎ ÄÅÅÞ, ÕÁÆƳ, ÆØ Å Ó, ÇÔº ; Ê ²Å 30 L/min, ¼., Ì Ö ±Ö ÇÌÐ. ÊÅÞ µ ÈÁ Å, Üßл Ô µè Æ Û ÜÊ, Î ¼À. ÊÅ Î Á, ÁÆ Þ Ý,. ÅÞÌ, Á Ý, Ö±ÅÞÌ ¼À ÅÅ Õ, Á Ü ÖμÀ Æ. Ð α Î 0 7.5, ¼ ¹, ÈØÜÐ 7.5, Å ÞºÎ, à µ, Ú Đ 7 ÃÄ ËÄ Fig.7 Schematic diagram of pressure balance at the keyhole wall (P abl recoil pressure, P g excess steam pressure, P h fluid pressure, P σ surface tension) 8 Â É ÓÒ Fig.8 Morphologies of cross section of a weld seam (a) and a porosity (b)

2 «: Á ¹ ÑÜ CO 2 ºÁ й 185 ¼ Ö, ØĐÎ Ü Ù Ú «ÕĐ, ÅÞÌØ Ý ; ØÜÐ 15 ¼, Ô, Ý, ¼À ßÁ Đ Ç,» Ü Å. Ò Ð ²ÅÞ, Ê, Ú ÎÈ, ÌÐ 37.5, ų Ï. ÌÐ ÈÒ» Ô Á Å, ÎÙÕÅÞ, ½ Ò, ¼, Þ Ý,., ŠƼ ÎÙÃÜ Æ, ¼Àß ½ Ý, ØÜ Ç ½, ± Æ Þ¾. à Ý, Ð ½, ÜÊ, µï, ¼À ³ ÐÈ. Ð ½ Ó (3 kw), ¼, ¼ ¼À ÆÍ Ñ Æ Æ, µ ², ¼À Ú ÐÈ, ³, μÀ Æ, λ à Â,. Ò Ð ½ ÅÞ 3.5 Æ 4 kw, ¼, ÜÊ Å Á¼À ³, ÙÃÜ Î¼À Æ. Ð ½ ÅÞ 5 kw, ØܼÀ Ô ², È ÐÛ ÄÅ,, Õ ÔÆÅ, Ç ÐÓ., Ð ½ ÅÞÎÁ È ÅÞ, ¼ ÅÞ, Ö Þ. à һ ÜÊ, Πһà µí ¼ ƼÀ Ð. Ò Ã Î 0.75 m/min Å Þ 1.75 m/min, ÜÊ Ó, µï Ê, Ã, ¼ÀÏ Ð, μÀ Æ Ð, Á Ó Æ,», ØÜ Ã Ó, Ð ÜÊ Õ ÕĐ, ¼À Ã, ÁÃ Þ Ý, à ÅÞ, Ý, ݵ¾ ; à Π1.75 m/min ÅÞ 2.25 m/min, Ö±, ÜÈØÜÃ, Çà ½Ù, Á Æ, Å Î Á Ý, ; ØÜà ² ¼ÀÏ Ð, Þ, Èà ÅÞ¼ Î, ÃÜ Æ. Ð ½ Æà ¾ ², ÙÃÜ ¼À ßÚ, Ü ³Ì. Ò Ã Î 2.25 m/min ÅÞ 2.75 m/min, ², ÃÜ Æ,, à РÜÊ ÕÜ, Á ÇÉ Ç ½ ÅƱ, ¼À Ã,, Á¼ÀÆ Ý, Ð Ê, Ù Ç. 4 Ù (1) ÓÞ CO 2 Ð ¼Å ¼Ã, ÌĐÜÃ Ý µõ». (2) Ê 35 L/min, Á Å, ÁÆ Ý Å, Ì ½; ¼ÀÅÅ ÕÖ±, Þ Ì Ã ¼À, Ì Ã». (3) Ð 37.5, Á Å, ØĐ Ü Ý, Á Đ Ç» Ü. Ð, ÅÞÌ Ð, ÃÜ Æ, Ê. ¼, 22.5 Ê. (4) Ð ½ 4 kw, ¼ Ƽ ¾ Á, ¼ ¼À Æ Æ, Øܼ À Ú Ð, μÀ Æ, Ê. (5) à Ó, µï ÊÈ, ¼ÀÏ Ð, ÃÜ Æ, ÊÈ. à 2.25 m/min, ²½ Æ Ã ÙÃÜ Æ,, à ¼. ÐÅ [1] Mikhail S, Antti S, Vladislav S, Alexander F. Opt Laser Technol, 2012; 44: 2064 [2] Reisgen U, Schleser M, Mokrov O, Ahmed E. Opt Laser Technol, 2012; 44: 255 [3] Ruggiero A, Tricarico L, Olabi A G, Benyounis K Y. Opt Laser Technol, 2011; 43: 82 [4] Yilbas B, Arif A, Abdul A. Opt Laser Technol, 2010; 42: 760 [5] Chang B H, Bai S J, Du D, Zhang H, Zhou Y. J Mater Process Technol, 2010; 210: 885 [6] Mei L F, Chen G Y, Jin X Z, Zhang Y, Wu Q. Opt Lasers Eng, 2009; 47: 1117 [7] Emel T, Eddy D, Alfred D, Erdinc K. Mater Des, 2009; 30: 1193 [8] Zhang X D, Chen W Z, Eiji A, Fukuhisa M. Trans Chin Weld Inst, 2002; 23(6): 51 ( Þ, º, Í, ³.  Á, 2002; 23(6): 51) [9] Zhao L, Zhang X D, Chen W Z, Bao G. Trans Chin Weld Inst, 2004; 25(1): 29 ( Ï, Þ, º,.  Á, 2004; 25(1): 29) [10] Zhang X H, Zhang X D, Chen W Z, Lei H D. Laser Technol, 2007; 31: 419 ( Í, Þ, º, Þ., 2007; 31: 419) [11] Zhao L, Zhang X D, Chen W Z, Wang J. Appl Laser, 2004;

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