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1 Journal of the Korean Ceramic Society Vol. 47, No. 3, pp. 256~261, DOI: /KCERS Effect of Al Alloy Composition on Physical and Crystallographical Properties of Plasma Electrolytic Oxidized Coatings I. Physical Properties of PEO Layer Bae-Yeon Kim, Deuk Yong Lee*, Yong-Nam Kim**, Min-Seok Jeon**, Jun Kwang Song**, Sung Youp Kim***, and Kwang Youp Kim*** Department of Advanced Materials Engineering, University of Incheon, Incheon , Korea *Department of Materials Engineering, Daelim University College, Anyang , Korea **Material Testing Center, Korea Testing Laboratory, Seoul , Korea ***MST Technology, Incheon , Korea (Received April 19, 2010; Revised May 11, 2010; Accepted May 13, 2010) v w y gq w, w w I. PEO d ½ Á *Á½ û**á **Á Ÿ**Á½ ***Á½Ÿ *** w œw * w w **w» x sƒ l ***MST Technology ( ; ; ) ABSTRACT Physical properties of Plasma electrolytic oxidized 8 different types of Al alloys, A-1100, A-2024, A-5052, A-6061, A-6063, A- 7075, ACD-7B and ACD-12 were investigated. The electrolyte for PEO was Na 2 SiO 3 solutions with NaOH and some alkali earthen metal salts. Porous layer near the surface of PEO coating was not found, and surface roughness Ra50 was below 2.5 µm. Surface roughness was affected by growth rate of plasma electrolytic oxidized layer, not by Si content in Al alloy. Key words a PEO, Coating, Crystal structure, Physical properties 1. PEO(Plasma Electrolytic Oxidation) Na 2 SiO 3 w w w Al, Mg, Ti, Zn k (passive metal) 350 V ~ 550 V ƒw k t y g y j».»» w» ƒ w, ù w ƒw 50 V w û. ƒ j» w ¼ k t Corresponding author : Bae-Yeon Kim bykim@incheon.ac.kr Tel : Fax : plasma(=micro-arc)ƒ wš w t y w. x y v w { y w yv w e» PEO x k t { w p.» 1970 wœ. p» k Fe š Carbonizing ù Nitriding ƒƒ ww. PEO 1990 z Keronite ƒ» A. L. Yerokhin w PEO w review paper t 1) wš, z» y w w y y» w. 256

2 v w y gq w, w w I. PEO d 257 Table 1. Typical Atomic Composition of Various Aluminum Alloys (%) Atoms Alloy Mg Cu Mn Cr Si Zn Al A-1100 <99.0 A balance A balance A balance A balance A balance ACD-7B balance ACD balance KSD 6701:2002 w q KSD2331:2003 e q w œ w PEO œ t w» x š t wš s w.» š ù t ã PEO œ w yw t w. PEO w k y v y v x» w w ü» gq, Plasma ù q mismatch w stressƒ ù,»» w { y x» t y v üyw w ù š., PEO» š ƒw w,. w t gq w w y ƒ. w d d. PEO w ƒ j», y, pulse s, bipolar j», duration time» œ. p» l w y w w w x yv w w. PEO w y v PEO œ t γ-alumina α-alumina š, 1-12) glassy phase 15-17) š5,13,14) š. mullite (3Al 2 O 3 2SiO 2 ) t Al-Si-O w w š w PEO œ ƒ ù w x ¾». q w 8 kw PEO e y t w w t gq d w d w w e w wš w. 2. x plate xk q w w w Table 1. ACD-7B ACD-12 k w» w Si ƒ, t Si t segregation w, k PEO coating w» w injection molding x t w. injection molding ACD- 7B ACD-12 t w j š ùkùš. q Ì 2 mm 50 mm 50 mm ƒœ w w, ACD 7B ACD12 φ50 mm t10 mm w. ü MST Technology ƒ w n-pec PEO e ~600 V, ~300 A e pulse w. w l p q w mm j» w, w w kj ü stirrer ew x w w. x w w Na 2 SiO 3 47«3y(2010)

3 258 ½ Á Á½ ûá Á ŸÁ½ Á½Ÿ Table 2. Formation of PEO Coating Layer with Various Applied Voltage in Na-Si-O System Metal Salts Electrolyte. Note that ø means Successful Coating, and ÿ Means Intermediate State, Ü Means Failure Alloy Volt A-1100 Ü ÿ ÿ ø ø ø ø ø Ü A-2024 Ü ÿ ø ø ÿ Ü A-5052 Ü ÿ ø ø Ü A-6061 Ü ÿ ÿ ø ø ø ÿ Ü A-6063 Ü ÿ ø ø ø ø ø ø Ü A-7075 Ü ø ø ÿ Ü ACD-7B Ü ÿ ø ÿ Ü ACD-12 Ü ÿ ÿ ÿ ø Ü w alkali earthen metal sww ph NaOH ƒw 2~3%. w w w z w x w., w PEO w w ƒ yw», ƒ x w ƒw ù 2 ƒ w» n w w w w. x Ì d» Automation Dr. Nix Quanix 7500 w, t Mitutoyo SJ- 301 w. t Wilson TUKON 2100 w d w, SEM Hitach FE-SEM S4700, EDXA Horiba 7200H w. 3. š Table 2 ƒ w v x k w., q» xk t w w w. øt ùkù w yw v x ùkü, ÿt ùkù y v x w ù, t ƒ eš, t kƒ w ùkü., Õ PEO w, ƒw ù,, pulse, bipolar, w w PEO w k. A1100 A6000 w ƒ f ùkü š w, w w. p Si w ü w wš ACD-7B ACD-12 Table 3. Thickness and Surface Roughness of PEO Coating Layer with Different Aluminum Alloys Properties Thickness(µm) Ra50(µm) Time 10 min. 20 min. 10 min. 20 min. A A A A A A ACD-7B ACD zw coating ù w. w Si w wš ƒw PEO w. Table 3 y v Ì t ùkü.» 10 v x z 10 v x w.» 10 v x 2µm/min w z 0.7 µm/min ƒ w. x» w t w y v x, z yv w v y v Á ww y v w w» diffusion y v ü diffusion ù w, diffusion» v x z w yv Ì w diffusion path ƒ w» š w. w wz

4 v w y gq w, w w I. PEO d 259 yv ̃ É» w f» w w micro-arc š w û ƒ micro-arc j»ƒ ³ew» w w. w, Siƒ ƒ injection w yv» x ƒ Si w w w system w 2/3 1.4 µm/min, z yv x w w 1/2 0.4 µm/min. A.L. Yerokhin 1) w Silicate ƒ 5~30% y v ̃ É š, ³ w» w x š,»œ» š šw. yv»œ ƒ t ù x, t ƒ ù., x y v t»œx. x w ü w Siƒ ùkü x, x w w Si w w Si x ùkü. w Siƒ 9.6%~12.0% w ACD-12 w y v t ƒ. ACD-12 w t ƒ t ƒ Si w w» yv w» q. t» PEO coating» wù, x t yw Ra µm. t» 1,6) w y v ̃ É ƒw w. w x» PEO y v ̃ É w plasmaƒ ³ew t»œ x foam-like structure š» 1). Table 4 yv f ùkü. d y v w d w. w ƒ ƒ ƒw w. w» 10 yv x k ƒƒ w ƒ 20 w ƒƒ ù w.»q(substrate) w» ù x.,»q Table 4. Hardness of PEO Layer Coated in type A Electrolyte Properties Hardness(Hv) Coating Time 0min 10min (%) 20 min (%) A % % A % % A % % A % % A % % A % % ACD-7B % % ACD % % Fig. 1. Scanning Electron Micrography of PEO caoted Al-1100 alloy. The dense aluminum oxide layer approximately 25 µm thick was formed at the surface of Al alloy. The PEO coated layer could be distinguished only from the scratch induced by polishing especially metal side. ƒ ƒ w ù kù,»q ƒ û ̃ f d probe w ¾ w û». w w w yv 20 z ƒ ƒw. ƒ s w ƒ û 60% 80% f, ƒs 35%. Fig. 1 A-1100 w 20 PEO w v SEM w. PEO yv Á»œ.» 47«3y(2010)

5 260 ½ Á Á½ ûá Á ŸÁ½ Á½Ÿ PEO x yv Á»œ d š š1,9,10) š w. yv d PEO t» ƒœ ùkù š, t ù ƒ»œ. w z x PEO w ƒ 450 C o 650 C o d, 800 o C δ -alumina θ -aluminaù 450 o C γ- alumina, y 1050 o C α-alumina w 1-18) x û» q. û œ PEO y v j α-alumina PEO y v ù ü w w w 1,9-11) t w»œ1,4) s k t w z ƒ. x PEO w x yv w xk defectù mismatch. w PEO w x y v x y, w û» r polishing w ¼ d w x scratch. w y v Ì ³ w. x w. 18) PEO w t x y d w e w PEO yv x w w» w š. ùƒ ú plasma ù š x CVD q 40 ppm/ C ùkü o 6~8 ppm/ o C ü û q y thermal mismatch þƒ mismatch ù. PEO v ù CVD, PVD w ~80 o C { û w y v x» thermal mismatchù thermal sterssƒ, w. Fig. 2 A-1100 w 100 w Fig. 2. Scanning Electron Micrography and EDXA result of 40 min. PEO treated Al-1100 alloy. The upper graph shows Al contents, and the lower graph reveals oxygen contents. From this result, the aluminum oxide layer approximately 30 µm thick was formed at the surface of Al alloy. The PEO coated layer could be distinguished only from the scratch induced by polishing especially metal side. Note that at the interface between Al alloy and aluminum oxide there is no defect. r x EDXA w. v ùküš š, v ùküš. w t yv x, w PEO y v ù interface yƒ»» š ywš. w -œ w wš y EDXA probe j»ƒ 1µm ü w y d y w š q w š q, w w p w ù mismatch PEO gq wù ù w š š w. w Fig. 1 ƒ» ƒœ w PEO t k š, PEO y v ü»œ wš. 4. Na 2 SiO 3 w w NaOH alkali earthen w wz

6 v w y gq w, w w I. PEO d 261 metal salt w w w w A-1100, A- 2024, A-5052, A-6061, A-6063, A-7075, ACD-7B ACD-12 w w plasma electrolytic coating w y v x k yv w. 1. q 8 w w PEO y v x g t ƒ k, 20 PEO 18 µm~ 29 µm yv x k. 2. PEO yv t w š» œ PEO gq w, t Ra(50 µm) 2.5 µm yw. 3. Si sw t Si w» yv w š, ƒ yv t ƒ w ùkü. Acknowledgment 2008 w w w. REFERENCES 1. A.L. Yerokhin, X. Nie, A. Leyland, A. Matthews, and S.J. Dowey, Plasma Electrolysis for Surface Engineering, Surface and Coatings Technology, (1999). 2. X. Nie, A. Leyland, H.W. Song, A.L. Yerokhin, S.J. Dowey, and A. Matthews, Thickness Effects on the Mechanical Properties of Micro-arc Discharge Oxide Coatings on Aluminum Alloys, Surface and Coatings Technology, (1999). 3. X. Nie, E.I. Meltis, J.C. Jiang, A. Leyland, A.L. Yerokin, and A. Matthews, Abrasive Waer/corrosion Properties and TEM Analysis of Al 2 O 3 Coatings Fabricated using Plasma Electrolysis, Surface and Coatings Technology, (2002). 4. A.L. Yerokin, A. Shatrov, V. Samsonov, P. Shahkov, A. Pilkington, A. Leyland, and A. Matthews, Oxide Ceramic Coatings on Aluminium Alloys Produced by a Pulsed Bipolar Plasma Electrolytic Oxidation Process, Surface and Coatings Technology, (2005). 5. H. Kalkanci and S.C. Kurnaz, The Effect of Process Parameters on Mullite-based Plasma Electrolytic Oxide Coatings, Surface and Coatings Technology, (2008). 6. F.-Y. Jin, K. Wang, M. Zhu, L.-R. Shen, J. Li, H.-H. Hong, and P. K. Chu, Infrared Reflection by Alumina Films Produced on Aluminum Alloy by Plasma Electrolytic Oxidation, Materials Chem. and Phys., (2009). 7. Y.-J. Oh, J.-I. Mun, and J.-H. Kim, Effect of Alloying Elements on Microstucture and Protective Proties of Al 2 O 3 Coatings Formed on Aluminum Alloy Substrates by Plasma Electrolysis, Surface and Coatings Technology, (2009). 8. G. Lv, W. Gu, H. Chen, W. Feng, M. L. Khosa, L. Li, E. Niu, G. Zhang, and S.-Z. Yang, Characteristic of Ceramic Coatings on Aluminum by Plasma Electrolytic Oxidation in Silicate and Phosphate Electrolyte, Applied Surface Science, (2006). 9. W. Xue, Z. Deng, R. Chen, T. Zhang, and H. Ma, Microstructure and Properties of Ceramic Coatings Produced on 2024 Aluminum Alloy by Microarc Oxidation, J. Materials Science, (2001). 10. J. Tian, Z. Luo, S. Qi, and X. Sun, Structure and Antiwear Behavior of Micro-arc Oxidized Coatings on Alluminum Alloy, Surface and Coatings Technology, (2002) 11. E. Arslan, Y. Totik, E.E. Demirci, Y. Vangolu, A. Alsaran, and I. Efeoglu, High Temperature Wear Behavior of Aluminum Oxide Layers by AC Micro Arc Oxidation, Surface and Coatings Technology, (2009)U 12. G. Sundararajan and L. R. Krishna, " Mechanisms Underlying the Formation of Thick Alumina Coatings Through the MAO Coating Technology, Surface and Coatings Technology, (2003)U 13. J.A. Curran and T.W. Clyne, The Thermal Conductivity of Plasma Electrolytic Oxide Coatings on Aluminum and Magnesium, Surface and Coatings Technology, (2005). 14. J.A. Curran and T.W. Clyne, Thermo-physical Properties of Plasma Electrolytic Oxide Coatings on Aluminum, Surface and Coatings Technology, (2005). 15. K. Wang, B.H. Koo, C.G. Lee, Y.J. Kim, S. Lee, and E. Byon, Effects of Hybrid Voltages on Oxide Formation on 6061 Al-Alloys During Plasma Electrolytic Oxidation, Chinese Journal of Aeronautics, (2009). 16. K. Wang, B.H. Koo, C.G. Lee, Y.J. Kim, S. Lee, and E. Byon, Effects of Electrolytes Variation on Formation of Oxide Layers of 6061 Al Alloys by Plasma Electrolytic Oxidation, Trans. Nonferrous Met. Soc. China, (2009). 17. J.A. Curran, H. Kalkanci, Yu. Magurova, and T.W. Clyne, Mullite-rich Plasma Electrolytic Oxide Coatings for Thermal Barrier Applications, Surface and Coatings Technology, (2007). 18. B.-Y. Kim, D. Y. Lee, Y.-N. Kim, M.-S. Jeon, W.-S. You, K. Y. Kim, Analysis of Oxide Coatings Formed on Al1050 alloy by Plasma Electrolytic OxidationOin KoreanP, J. Kor. Ceram. Soc., 46 [3] (2009). 47«3y(2010)