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1 A Study on the Machining Characteristics of the Electropolishing of Aluminum ( ) - 1 -

2 A Study on the Machining Characteristics of the Electropolishing of Aluminum

3 ABSTRACT List of Figures List of Table

5 .,. AL (Al 1050). 1., 7A/cm 2, 200sec , 5mm

6 Rmax () 1.8 Rmax

7 ABSTRACT This study is aimed to obtain the basic material for reviewing the research characteristics and the possibility of alternatives to processing stainless steel through the study on electropolishing characteristic of aluminium. As the study on the electropolishing of aluminium alloy has not been published yet, this study can be contributed to the basis of Korea industrial development because the advantage of aluminium characteristic such as light and corrosion resistance has not been fully used in industrial field. In this study the purest aluminium, AL 1050 has been used. As the study has been conducted in pure condition, it can be applied to other aluminium alloy. The results were as follows: 1. The density of electric current is important factor in electropolishing of aluminium. The surface smoothness should be more than 7A/cm2 even in a short processing time And in more than 200sec of processing time, improving rate of smoothness is slowdown. 2. Excellent surface smoothness can be obtaine d at the 78 of electrolyte and the good result of electropolishing can acquired in a electrode gap of 5mm

8 3. As there is a limitation to improve the high surface smoothness, the surface smoothness shall be maintained less than 1.8m Rmax in pre-processing stage in order to achieve the highly smooth surface less than 0.5m

9 List of Figures Fig. 2-1 Principle of electropolishing 27 Fig. 2-2 Electropolishing mechanism 30 Fig. 2-3 Current density-voltage curve of electropolishing 31 Fig. 2-4 Surface smoothing effect of electropolishing 37 Fig. 2-5 Drawing, lapping, and electropolishing 37 Fig. 2-6 Deburring effect of electropolishing 38 Fig. 2-7 Cleaning effect of electropolishing 38 Fig. 2-8 Practical application examples of electropolishing 42 Fig. 2-9 Industry application examples of electropolishing 43 Fig Effects of impurities on the electrical conductivity of Al 47 Fig. 3-1 Experimental setup 51 Fig. 4-1 Current density-voltage curve of Al Fig. 4-2 Optical micrographs for various current density 54 Fig. 4-3 Relationship between surface roughness and current density 55 Fig. 4-4 Optical micrographs for various polishing time 58 Fig. 4-5 Relationship between surface roughness and polishing time 59 Fig. 4-6 Optical micrographs for various electrolyte temperature 62 Fig. 4-7 Relationship between surface roughness and electrolyte temperature 63 Fig. 4-8 Relationship between surface roughness and electrode gap 65 Fig. 4-9 Relationship between surface roughness of before and after electropolishing

10 Fig Optical micrographs of Al Fig Surface profiles between before and after electropolishing 72 Fig Metallographic micrographs of Al

11 List of Table Table 1-1 Classification of aluminum alloys 5 Table 1-2 Chemical composition of aluminum alloys 10 Table 1-3 Mechanical property of industrial aluminum alloys 14 Table 1-4 Mechanical property of pure aluminum alloys 15 Table 1-5 Transformation of mechanical property by rolling 16 process Table 1-6 Corrosion tendency of aluminum 17 Table 1-7 General characteristic of aluminum alloy 24 Table 2-1 Example of electrolyte 45 Table 3-1 Chemical composition of Al Table 3-2 Mechanical property of Al Table 3-3 Test condition

14 - 14 -

16 1) Table 1-1 Classification of aluminum alloys SERIES ALLOY APPLICATION CHARACTER 1000 SERIES 1235 FOIL STOCK 1050 FIN STOCK, COSMETIC CAP UTENSILS, NAME PLATE LITHO SHEET ARCHITECTURAL PANEL EVAPORATOR 99.0,,. ( 99.0 ~ 99.5%) Fe Si. 1000,,. 1235, 1100, 1050, ,

17 2000 SERIES 3000 SERIES 1145 FOIL STOCK 1100 FIN STOCK SOLAR COLLECTOR, CONDENSER CASE 2014 AIRCRAFT STRUCTURES 2017 MACHINE PRODUCTS FITTINGS 2024 AIRCRAFT STRUCTURES 3003 ARCHITECTURAL MATERIALS UTENSILS FIN STOCK 1100, Cu,. 2024, (CLAD). 1100Mn (1.5%) 20%., (DEEP DRAWING)

18 4000 SERIES 5000 SERIES 3004 CAN BODY 3105 P.P CAP 4343 WELDING WIRE 4043 RADIATOR FIN CLAD 5005 AUTOMOTIVE PARTS ARCHITECTURAL PARTS 5052 CONTAINER, VAN TRUCK AUTOMOTIVE PARTS CAN END 5082 CAN TAB, CAN END, Mn1.2% 3003,,, Mn 1.2% + Mg 1.0% 3004DEEP DRAWING, BODY,. Si,. 4000, BRAZING ALLOY. Mg. Mg Mg Mn 0.8%Mg1.25%Mn,.,. 5052, 5005, ,,,, ,

19 6000 SERIES 5182 CAN END 5083 MARINE PARTS DEFENCE PARTS TRANSPORTATION EQUIPMENTS 6061 AUTOMOTIVE PARTS MARINE PARTS MACHINE PARTS RAILROAD CARS 6063 MACHINE PARTS SEA CONTAINER, END, LNG , 7000,, 6061.,

20 7000 SERIES 8000 SERIES AIRCRAFT STRUCTURES MACHINE PARTS AUTOMOTIVE PARTS AIRCRAFT STRUCTURES Zn. 0.2%~0.3%Cr. Cu,. (Duralumin) P.P CAP 8000 P.P CAP

21 Table 1-2 Chemical composition of aluminum alloys ALLOY Si Fe Cu Mn Mg Cr Ni Zn Ti OTHERS AL(%) EACH TOTAL Si+Fe Si+Fe Si+Fe Si+Fe Remainder

25 2) Table 1-3 Mechanical property of industrial aluminum alloys (8) (20) () Al % Al 96.5% (100) cal/g (20~100) (Cu68.94% ) %

26 (8) 3) Table 1-4 Mechanical property of pure Aluminum alloys kg/mm 2 kg/mm 2 % % 75% H B

27 . Table 1-5 Transformation of mechanical property by rolling process kg/mm 2 kg/mm 2 % H B Al 50% 9 Al 12 75% 17 Al

28 4),.. Table 1-6. (8) Table 1-6 Corrosion tendency of aluminum Al,., (Oxalic acid).,,,,. 80%...,.,,

29 . (Cl), (Br), (I), (Hg), (S). Al. (Cu) (Ag), (Ni), (Fe). (Mg), (Mn). 5) (Cu)

30 (Si) (Mg)

31 (Fe) (Mn) (Ni)

32 (Cr) (Ti) (Zn)

33 (Ca), (Na, Li)

34 (Be), (V, Zr)

35 6) Table 1-7 General characteristic of aluminum alloys (9) 2.7Fe 7.87, Cu8.9 1/3..,,,. Fe 5, Cu 60%.,. LNG,..,,

36 ,,,, Case.. 3%

37 (+), (-),,.,.,,, () (). (1) Fig. 2-1,

38 a)initial state of electropolishing process b)intermediation of electropolishing process Fig The principle of electropolishing

39 Ben Franklin,.. (10) Fig (7)~(8), Fig , (pit). (11)

40 Fig AB, BC. Plateau CD,. (pit) plateau,. plateau. (11),.,

41 Fig. 2-2 Electropolishing mechanism (2)

42 Fig. 2-3 Current density-voltage curve of electropolishing

43 (1) 2.2 1) 5080%,.. 2) super-passivation (12)., (Bailby layer)

44 ,.. 3) / 4) (Burr), Fig. 2-6 (edge )

45 5) (electrocleaning). ( )., (cathodic cleaning), (direct cleaning)...,.. (anodic cleaning), ( )

46 (reve rse cleaning),.,.. (acid dip).,......,. PR,. PR

47 ., ( ).,,,

48 Fig. 2-4 Surface smoothing effect of electropolishing Fig. 2-5 Drawing, Lapping, and Electropolishing

49 Fig. 2-6 Deburring effect of electropolishing (1) Fig 2-7 Cleaning effect of electropolishing

50 2.3,, /,,,,,.,, LCD,,,,,,,.,, ()., (electropolishing, electrolytic polishing)., (fittings)

51 ,. Fig. 2-9 Chemical supply system, Gas cabinet, TFT LCD cleaner,,,, Dry. (fittings), (tubes).,., STS316L,,,.. (1), (Stainless steel),.,,,

52 .,,,

53 (a) Pipe 1 (b) Pipe 2 (c) Pipe 3 (d) Hygienic kitchen utensils (1) Fig. 2-8 Practical application examples of electropolishing

54 (a) Chemical supply unit (b) Gas cabinet (c) TFT LCD cleaner Fig. 2-9 Industry application examples of electropolishing

55 2.4,,,,,,,,.,,,,,..,, (V),,, Fig Table2-1. (2)-(5)

56 Table 2-1 Example of electrolyte BASE ALLOY ELECTRO COMPOSITION Stainless steel High Nickel STS316L Electrolyte 1 Electrolyte 1 : phosphoric acid 50%(vol) sulphuric acid 20%(vol) distilled water 30%(vol) Nickel 200 Electrolyte 2, 3 and 4 Electrolyte 2 : phosphoric acid 650 sulphuric acid 350 Monel 400 Electrolyte 2, 3 and 4 Electrolyte 3 : phosphoric acid 1 gal chromic acid 1lb Hastelloy C-22 Electrolyte 3 and 4 Electrolyte 4 : phosphoric acid 400 sulfuric acid 300 Inconel 718 Electrolyte 4 ethylene glycol 300 Copper Zinc Pure Cu Electrolyte 5 Monophase Electrolyte 6 or 7 alloy Twocomponent alloy Multicomponent alloy Pure Zn Electrolyte 8 Zn alloy Electrolyte 5 : orthophosphoric acid 690g/ Methyl alcohol 470 g/ Electrolyte 6 : orthophosphoric acid 684g/ ethylene glycol 111 water 500 g/ Electrolyte 7 : orthophosphoric acid 684g/ ammonium acetate 20 g/ ethylene glycol 111 water 500 g/ Electrolyte 8 : ethylene glycol 100 Ethanol 400 Sodium thiocyanate 50g

57 Zn-Al-Cu(Al 25% ) Zn-Al-Cu(Cu 10% ) Electrolyte 9 Electrolyte 10 Zn-Al-Cu Electrolyte 8 Electrolyte 9 : perchloric acid 25 Methanol 575 Nitric acid 10 Electrolyte 10 : 5% solution perchloric acid in ethanol

58 Electric conductivity (m/ ) Impurity(%) Fig Effects of impurities on the electrical conductivity of Al

59 3 Fig.3-1 (power supply). (-) (Stainless steel jig)(+). Power supply 50V, 50A power supply (jig). Process bath 2x 2. (Al 1050) Table 3-1.,,,, (),,,. Table

60 Table 3-1 Chemical composition of Al 1050(%) Symbol for element Si Fe Cu Mn Mg Zn Ti Al Chemical composition (%) Table 3-2 Mechanical property of Al 1050 Brinell Yield / Strength Kgf/mm 2 Tensil Strength Kgf/mm 2 Elongation Thickness 1.6mm % Hardness Kgf/mm 2 Kgf/mm 2 Kgf/mm H H H

61 Table 3-3 Test condition Power supply 50V, 50A DC Workpiece Al 1050 (anode) 2 cm 2 cm (t=0.5 mm) Phosporic acid 90% Electrolyte Cromic acid, to saturation Distilled water, as requried Electrode (cathode) Jig Surface roughness tester Cu Stainless steel Form Talysurf Surface measurement Kan Scope 3.0 Metallographic measurement HITACHI S

62 (a) The schematic of experiment (b) Process bath (c) Test equipment Fig. 3-1 Experimental setup

63 4 Fig. 4-1 Al mm, 87, (H 3 PO 4 ), (Cr 2 O 3 ), (H 2 O).. Current density (A/cm 2 ) Workpiece Al 1050 Temperature 87 Electrode gap 5mm Electrolyte H 3 PO 4 +Cr 2 O 3 +H 2 O Electrolyte : Phosphoric acid (H 3 PO 4 ) 90% Distilled water (H 2 O), as required Chromic acid (Cr 2 O 3 ), to saturation Voltage (V) Fig. 4-1 Current density-voltage curve of Al

64 4-1. Fig. 4-2, Fig Ra, 1.6Rmax. 150sec, 46 5mm, (H 3 PO 4 ), (Cr 2 O 3 ), (H 2 O)., 7A/cm 2. 03A/cm 2, 37A/cm 2, 7A/cm

65 (a) 1 A/cm 2 (b) 7 A/cm 2 (c) 10 A/cm 2 Fig. 4-2 Optical micrographs for various current density

66 Surface roughness (mm) R max R a Before polishing 1.6 mm R max 0.3 mm R a Workpiece Al 1050 Polishing time 150s Temperature 46 o C Electrode gap 5mm Electrolyte H 3 PO 4 +Cr 2 O 3 +H 2 O Current density (A/cm 2 ) Fig. 4-3 Relationship between surface roughness and current density

67 4-2. Fig. 4-4, Fig Ra, 1.6Rmax. 7.0A/cm 2, 65, 5mm. (H 3 PO 4 ), (Cr 2 O 3 ), (H 2 O). 200sec. 050sec, sec,, sec.,,

68 ,.,,.,

69 (a) 50 sec (b) 200 sec (c) 400 sec Fig. 4-4 Optical micrographs for various polishing time

70 Surface roughness (mm) R max R a Before polishing 1.6 mm R max 0.3 mm R a Workpiece Al 1050 Current density 7 A/cm 2 Temperature 65 o C Electrode gap 5mm Electrolyte H 3 PO 4 +Cr 2 O 3 +H 2 O Time (sec) Fig. 4-5 Relationship between surface roughness and polishing time

71 4-3. Fig. 4-6, Fig Ra, 1.6Rmax, 6A/cm 2, 120sec, 3mm. (H 3 PO 4 ), (Cr 2 O 3 ), (H 2 O), Al , 78.,.,, ()

72 Fig. 4-6 (a), (b), (c), ,,

73 (a) 28 (b) 78 (c) 90 Fig. 4-6 Optical micrographs for various electrolyte temperature

74 2 R max R a Surface roughness (mm) 1 Workpiece Al 1050 Current density 6 A/cm 2 Polishing time 120s Electrode gap 3mm Electrolyte H 3 PO 4 +Cr 2 O 3 +H 2 O Before polishing 1.6 mm R max 0.3 mm R a Temperature ( o C) Fig. 4-7 Relationship between surface roughness and electrolyte temperature

75 A/cm 2, 80sec, 72, (H 3 PO 4 ), (Cr 2 O 3 ), (H 2 O) 0.2Ra, 1.9Rmax Fig. 4-8., (5mm ),.,. Al

76 2.5 R max R a Surface roughness (mm) Before polishing 1.9mmR max 0.2mmR a Workpiece Al 1050 Current density 6 A/cm 2 Polishing time 80s Temperature 72 o C Electrolyte H 3 PO 4 +Cr 2 O 3 +H 2 O Electrode gap (mm) Fig. 4-8 Relationship between surface roughness and electrode gap

77 4-5. () #1200, #1500, #2000 () Fig A/cm 2, 120sec, 5mm, 68, (H 3 PO 4 ), (Cr 2 O 3 ), (H 2 O). # Rmax() 1.72Rmax, # Rmax(). #2000 () 1.96 Rmax 1.35Rmax.,., ()

78 . (),, ()

79 Workpiece Al Current density 7 A/cm 2 Surface roughness, R max (mm) #1200 Abrasive #1500 Abrasive #2000 Abrasive Polishing time 120s Electrode gap 5mm Temperature 68 o C Electrolyte H 3 PO 4 +Cr 2 O 3 +H 2 O 1.4 Before EP After EP Fig. 4-9 Relationship between surface roughness of before and after electropolishing

80 4-6. Al 1050,. Fig. 4-10,, Fig (profile).. Fig (a), (b),.,,,. Fig (c) (pit). (pit),

81 4-7. Al 1050 Al Al Table 1-2 Al Table 2-1,,. (Mn) (base)al 3000, (Si) Al 4000, (Mg) Al 5000, - (Mg-Si) Al 6000, - (Zr-Mg) Al

82 (a) Before electropolishing (b) After electropolishing Fig Optical micrographs of Al

83 (a) Before electropolishing (b) After electropolishing Fig Surface profiles between before and after electropolishing

84 (a) Before electropolishing (b) After electropolishing (c) Pit mark Fig Metallographic micrographs of Al

85 5 AL 1050,,,,.. 1.,, 7A/cm 2. 2.,,, 200sec,

86 ,. 4. 5mm,, Rmax () 1.8 Rmax

87 1. E. S. Lee, J. W. Park and Y. H. Moon, Development of Ultra Clean Machining Technology with Electrolytic Polishing Process, International Journal of KSPE, Vol. 2, No. 1, 2001, pp R. Rokicki, "Electropolishing of high nickel alloy", Journal of Metal Finishing, 91(6), 1993, pp R. Kovacheva, R. Dafinova and N. Gidikova, "Electropolishing of copper and copper base alloy for metallographic inspection", Praktische Metallographic 30, 1993, pp R. Kovacheva, N. Gidikova and A. Lilova, "A new Electropolishing technique for metallographic specimen preparation of zinc and zinc alloy", Materials Characterization, 28, 1992, pp R. Kovacheva, S. Zadgorsky and A. Lilova, "Electrolytic polishing of Zn-Al-Cu alloys", Praktische Metallographic 29, 1992, pp Robert L. Davis, An Electropolishing Primer, Products Finishing, 1995, pp Internet data of WOOJOO Precision Co., Ltd, URL : Technical Information

88 8. Y. H. Yum, Seoul University, Mechanical Metallurgy, 1988, pp Internet data of ILIJN Enterprise Co., Ltd., URL : Property of Aluminum 10. T. Hryniewicz, "Towards a new conception of electropolishing of metals and alloys", Processings of First East-West Symposium on Materials and Processes, UK, 1990, pp J. P. Caire, E. B. Chainet and N. P. Valenti, "Study of a new stainless steel electropolishing process", Proceedings of the 80th AESF Annual Technical Conference, USA, 1993, pp S. Ganesh Sundara Raman and K. A. Padmanabhan, "Effect of electropolishing on the room temperature low-cycle fatigue behavior of AISI 304LN stainless steel", Int. J. Fatigue, Vol. 17, No. 3, 1995, pp

Alloy Group Material Al 1000,,, Cu Mg 2000 ( 2219 ) Rivet, Mn 3000 Al,,, Si 4000 Mg 5000 Mg Si 6000, Zn 7000, Mg Table 2 Al (%

Alloy Group Material Al 1000,,, Cu Mg 2000 ( 2219 ) Rivet, Mn 3000 Al,,, Si 4000 Mg 5000 Mg Si 6000, Zn 7000, Mg Table 2 Al (% http://wwwtechnonetcokr (Aluminum & Aluminum BasedAlloy) : LG 1 Aluminum Table 1, 2 1000 7000 4 Al 990% Al 1XXX AlCu 2XXX AlMn 3XXX AlSi 4XXX AlMg 5XXX AlMgSi 6XXX AlZn(Mg, Cu) 7XXX 8XXX ( ) 9XXX Fig 1