Metal Casting Technologies : MCT SEP 2018 (3RD QRT) WHOS WHO OF METALS
30 www.metals.rala.com.au METAL Casting Technologies 3rd Quarter 2018 31 There is also a need to refine the eutectic cell size in Sr modified Al-Si to reduce to the chances of damaging dispersed porosity . Recent work suggests that this can be achieved by Sr + CrB2 additions, with the CrB2 particles nucleating the eutectic cells in place of AlP . In addition to refinement of primary Al grain size, eutectic cell size, and the form of eutectic Si within these cells there is ongoing interest in refinement of the primary Al dendrites via reduction in the secondary dendrite arm spacing (SDAS). The smaller this spacing the more uniform is the distribution of alloying elements and intermetallic phases, the less is the chance of any interdendritic porosity, the higher is the strength and ductility, and the better is the response to any subsequent heat treatment. An increase in overall alloy content in Al-Si- Cu-Mg decreases SDAS for a given cooling rate [51,52]. Also, finer SDAS are produced by increased solidification rate during solidification of a given alloy. Hence the properties of Al alloys are section-sensitive in that thinner sections of Al castings tend to show better integrity and mechanical properties than thicker sections. Likewise, gravity die castings will generally be superior to conventional sand castings. For a given cooling rate during solidification SDAS is reduced by 35% when the Si content is increased from 4 to 9wt% . Attempts have been made to refine SDAS in TECHNICAL FEATURE REFERENCES: 1. J.T.H. Pearce: “Antimony in Cast Irons”. Metal Casting Technologies (2017) Vol.63 4th Quarter pp.20-23. 2. J.F. Meredith: “Modification of aluminium-silicon foundry alloys”. Metal Casting Technologies (2012) Vol.58 No.2 June pp.36-37. 3. W. Wang & J.E. Gruzleski: “Interactive Effects During Sodium or Strontium Treatment of Antimony Containing A356 Alloy”. AFS Transactions (1990) Vol.98 pp.227-234. 4. S. Khan & R. Elliott: “Effects of antimony on the growth kinetics of aluminium- silicon eutectic alloys”. J. Mat. Sci. (1994) Vol.29 pp.736-741. 5. S. Boontein et Al: “Reduction in secondary dendrite arm spacing in cast aluminium alloy A356 by Sb addition”. Int. J. of Cast Metals Res. (2011) Vol.24 pp108-112. 6. G.K. Sigworth: “The modification of Al-Si casting alloys: important practical and theoretical aspects”. Int. J. of Metalcasting (2008) Vol.2(2) pp.19-40. 7. J. Campbell & M. Tiryakioglu: “Review of effect of P and Sr on modification and porosity development in Al-Si alloys”. Mat. Sci. & Technology (2010) Vol.26 No.3 pp.262-268. 8. M. Faraji et Al: “Effect of Phosphorus and Strontium Additions on Formation Temperature and Nucleation Density of Primary Silicon in Al-19Wt Pct. Si Alloy and Their Effect on Eutectic Temperature”. Met. & Mat. Trans. A (2009) Vol.40A July pp.1710-1715 9. B.L. Tuttle et Al: “The Effect of Trace Amounts of Antimony on the Structure and Properties of Aluminum Alloy A356.2”. AFS Transactions (1991) Vol. 99 pp.7–16. 10. M. Garat et Al: “State of the Art Use of Sb-, Na- and Sr-modified Al-Si Casting Alloys”. AFS Transactions (1992) Vol.100 pp.821-832. 11. E.N. Pan et Al: “Roles of Sr and Sb on Silicon Modification of A356 Aluminum Alloys”. AFS Transactions (1994) Vol.102 pp.609–629. 12. M. Stackpool et Al: “Application of an electrochemical sensor to measure sodium levels in aluminium alloys”. Foundryman (2003) Vol.96 September pp.218-220. 13. J.R. Denton & J.A. Spittle: “Solidification and susceptibility to hydrogen absorption of Al-Si alloys containing strontium”. Mat. Sci. & Technol. (1985) Vol.1 No.4 pp.305-311. 14. C.M. Dinnis et Al: “Eutectic Morphology and Porosity in Unmodified and Strontium Modified Al-Si Alloys”. AFS Transactions (2005) Vol.113 pp.99-106. 15. S. McDonald et Al: “Unintentional Effects of Sr Additions in Al-Si Foundry Alloys”. (2007) Proceedings of Shape Casting: The 2nd Int. Symposium. Eds. P.N. Crepeau et Al, TMS, pp.59-66. 16. G. Sigworth et Al: “The modification of Al-Si casting alloys: important practical and theoretical aspects”. Int. J. of Metalcasting (2009) Vol.3 No.1 pp.65-78. 17. N.S. Tiedje et Al: “Feeding and Distribution of Porosity in Cast Al-Si Alloys as Function of Alloy Composition and Modification”. Met. & Mat. Trans. A (2012) Vol.43A pp.4846-4858. 18. N.S. Tiedje et Al: “A new multi-zone model for porosity distribution in Al-Si casting alloys”. Acta Mat. (2013) Vol.61 pp.3037-3049. 19. S.Z. Lu & A. Hellawell: “The Mechanism of silicon Modification in Aluminium- Silicon Alloys: Impurity Induced Twinning”. Met. Trans. A (1987) Vol.18A pp.1721- 1733. 20. K. Nogita et Al: “Evaluation of Silicon Twinning in Hypo-Eutectic Al-Si Alloys”. Mat. Trans. (2003) Vol.44 No.4 pp.625-628. 21. M.G. Day & A. Hellawell: “The Microstructure and Crystallography of Aluminium -Silicon Eutectic Alloys”. Proceedings of Royal Society (1968) Vol. A305 pp.473- 491. 22. M.G. Day: “Use of Scanning Electron Microscopy to Investigate Aluminium/ Silicon and Iron/Graphite Eutectic Systems”. Journal of Metals (1969) Vol.21 No.4 April pp.31-34. 23. M. Timpel et Al: “The role of strontium in modifying aluminium-silicon alloys”. Acta Materialia (2012) Vol.60 pp.3920-3928. 24. Z. Fangqlu & L. Xiaoyun: “Functions and mechanisms of modification elements in eutectic solidification of Al-Si alloys: A brief review”. China Foundry (2014) Vol.11 No.4 pp.287-295. 25. A.K. Dahle et Al: “Eutectic modification and microstructure development in Al-Si Alloys”. Mat. Sci. & Eng. A (2005) Vol.413-414 December pp. 243-248. 26. J. Campbell: Entrainment Defects”. Materials Sci. & Tech. (2006) Vol.22 pp.127- 145. 27. Q. Chen & W.D. Griffiths: “The Effect of Sr Modifier Additions on Double Oxide Film Defects in 2L99 Alloy Castings”. Met. & Mat. Transactions A (2017) Vol.48A pp.5688-5698. 28. S.D. McDonald et Al: “Eutectic grain size and strontium concentration in hypoeutectic aluminium-silicon alloys”. J. of Alloys & Compounds (2006) Vol.422 pp.184-191. 29. W.S. Ebhota & T.C. Jen: “Effects of Modification Techniques on Mechanical Properties of Al-Si Cast Alloys”. Ch. 4 in “Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical Behaviour and Applications”, Ed. S. Sivasataran (2017) http://dx.doi.org/10.5772/intechopen.70391 30. S. Markovic et Al: “Antimony as a modifier of a piston alloy”. Diecasting World (2002) March pp.22-24. 31. S.Z. Lu & A. Hellawell: “Growth mechanisms of silicon in Al-Si alloys”. J. of Crystal Growth (1985) Vol.73(2) pp.316-328. 32. K . Nogita et Al: “Eutectic Modification of Al-Si Alloys with Rare Earth Metals”. Mat. Trans (2004) Vol.45 No.2 pp.323-326. 33. K . Nogita & A.K . Dahle: “Eutectic Growth Mode in Strontium, Antimony and Phosphorus Modified Hypoeutectic Al-Si Foundry Alloys”. Mat. Trans. (2001) Vol.42. No.3 pp.393-396 . 34. K . Nogita et Al: “The role of trace element segregation in the eutectic modification of hypoeutectic Al-Si alloys”. J. of Alloys & Compounds (2010) Vol.489 pp.415-420. 35. A.K . Prasada Rao et Al: “on the modification and segregation of Sb in Al-7Si alloy during solidification”. Mat. Letters (2008) Vol.62 pp.2013-2016. 36. J. Chen et Al: “Study on Eutectic Microstructure and Modification Mechanism of Al-Si Alloys”. Mat. Sci. Forum (2017) Vol.877 pp.97-103. 3 7. F . Guo et Al: “Enhanced nucleation and refinement of eutectic Si by high number-density nano-particles in Al-10Si-0 .5Sb alloys”. Materials & Design (2017) Vol.117 March pp.382-389 . 38. H . Li and Q. Chai: “Study on Modification Mechanism of Antimony in Al-Si cast alloys”. Advanced Materials Research (2011) Vol.197-198 pp.1079-1085. 39. W . Wang & J.E. Gruzleski: “Antimony-modifier Interactions in Aluminium Foundry Melts – Part 1: Antimony -Strontium Interactions, Part 2: Antimony- Sodium and Antimony-Strontium-Sodium Interactions”. Cast Metals (1992) Vol.5 Part 1 pp.20-28, Part 2 pp.29-34. 40. M. Tokar et Al: “The effect of Strontium and Antimony on the mechanical properties of Al-Si alloys”. Mat. Sci. & Eng. (2014) Vol.39 pp .69 -79. 41. S. Farahany et Al: “Evaluations of antimony and strontium interaction in an Al-Si-Cu-Zn die cast alloy”. Thermochimica Acta (2014) Vol.584 pp.72-78. 42. S. Farahany et Al: “Combined effect of strontium modifier and antimony refiner on texture and growth modes of eutectic phase in an Al-11Si-2Cu-0 .8Zn-o.6Fe cast alloy”. Phil. Mag. Letters (2015) Vol.95 No.12 pp.587-593. 43. Y . Sun et Al: “Effects of Complex Modification by Sr-Sb on the Microstructures and Mechanical Properties of Al-18wt% Mg2Si-4.5cu Alloys”. Materials (2016) Vol.9 pp .157 44. Z . Wang et Al: “Modification and refinement effects of Sb and Sr on Mg17Al12 and Mg2Si phases in Mg-12Al-0.7Si alloy”. China Foundry (2016) Vol.13 No.5 pp.310-315. 45. H .Y . Wang et Al: “Refinement and modification of primary Mg2Si in an Al-20Mg2Si alloy by a combined addition of yttrium and antimony”. CrystEngComm (2017) Royal Society of Chemistry DOI: 10.1039/c7ce01309d. 46. Y . Birol: “Interaction of grain refinement with B and modification with Sr in aluminium foundry alloys”. Mat. Sci. & Technology (2012) Vol.28(1) pp.70-76. 4 7. H . Tahiri et Al: “Effect of Sr-grain refining – Si interactions on the microstructural characteristics of Al-Si hypoeutectic alloys”. Int. J. of Metalcasting (2018) Vol.12(2) pp.343-361. 48. A.K. Prada Rao et Al: “Microstructural feature of as-cast A356 alloy inoculated with Sr, Sb modifiers and Al-Ti-C grain refiners simultaneously”. Mat. Letters (2008) Vol,62 pp.273-275. 49. A.K. Dahle et Al: “Refinement of Al-Si Eutectic Grains – A Novel Method to Produce High Integrity Al-Si Castings”. Proceedings of 10th Asian Foundry Congress (AFC-10) Nagoya, Japan. May 21-24 (2008) pp.227-232. 50. J.H. Li et Al: “Simultaneously refining eutectic grain and modifying eutectic Si in Al-10Si-0.3Mg alloys by Sr and CrB2 additions”. Int. J. of Cast Metals Res. (2016) Vol.29(3) pp.158-173. 51. M. Easton et Al: “Effect of Alloy Composition on the Dendrite Arm Spacing of Multicomponent Aluminium Alloys”. Met. & Mat. Trans. A (2010) Vol.41 No.6 pp.1528-1538. 52. T . Sivarupan et Al: “Alloy Composition and Dendrite Arm Spacing in Al-Si-Cu- Mg-Fe Alloys”. Met. & Mat. Trans. A (2013) Vol.44 No.9 pp .4071-4080. 53. S. Boontein et Al: “Effect of minor Sb additions on SDAS, age hardening and mechanical properties of A356 aluminium alloy casting”. Mat. Sci. Forum (2006) Vols.519-521 pp.537-542. 54. S. Boontein et Al: “Reduction in secondary dendrite arm spacing in cast aluminium alloy A356 by Sb addition”. Int. J. of Cast Metals Res. (2011) Vol.24(2) pp.108-112. 55. H .L. Zhao et Al: “Grain and dendrite refinement of A356 alloy with Al-Ti-C -RE master alloy”. Rare Metals (2013) Vol.32(1) pp.12-17. 56. R. Ahmad & M.B .A. Asmael: “Influence of Lanthanum on Solidification, Microstructure and Mechanical Properties of Eutectic Al-Si Piston Alloy”. JMEPEG (2016) Vol.25 pp.2799-2813. 5 7. P. Pandee et Al: “Microstructural evolution and mechanical properties of Al-7Si- 0.3Mg alloys with erbium additions”. J. of Alloys & Compounds (2017) Vol.728 pp.844-853. 58. C .G. Anderson: “The metallurgy of antimony”. Chemie der Erde (2012) Vol.72 S4 pp.3 -8. 59. R.G. Cooper & A.P. Harrison: “The exposure to and health effects of antimony”. Indian J. of Occupational & Environmental Medicine (2009) Vol.13(1) pp.3-10. 60. A.R. Bailey & L.E . Samuels: “Foundry Metallography”. (1971) Met. Services, England, pp.33-39 . hypoeutectic Al alloys, especially Al-7Si-0.3Mg, via additions of Sb [53,54] and RE metals such as Cerium (Ce), Lanthanum (La) and Erbium (Er) [55-57]. For Sb the most effective reduction in SDAS was at 0.12wt%Sb  with levels of 0.18- 0.3wt% giving larger but less variable values of SDAS. As for Sb, it has been found for both Ce  and La  that there is an optimum addition needed for SDAS refinement, with SDAS increasing again at levels above this amount. It is of interest to note that Er is said to not only reduce SDAS, but also to refine the primary Al grain size and modify eutectic Si into a fine fibrous form . Ce, La and other Re also demonstrate a modifying effect. It is believed that, due to the low partition coefficient of Sb in α-Al solid solution, the liquid at the solid α-Al dendrite surface can become enriched in Sb even at relatively small additions of Sb in the alloy. This build-up then causes additional constitutional undercooling in liquid at the interface leading to a greater degree of dendrite branching, similar to the effect of Cu in Al-Cu alloys. It is also thought that Sb reduces dendrite arm coarsening . Like Sb. the RE metals, Ce, La and Er with low solubility in α-Al also segregate to interface liquid. At higher than optimum additions of Sb and RE the loss in SDAS refinement may result from a reduction in the degree of constitutional undercooling as these elements come out of the liquid to form intermetallic compounds. Primary Sb production is now limited to a few countries with the greatest volume being produced in China , a country also noted for its sources of RE metals. Future R&D work in China and in other countries using Sb treatment may well provide a better understanding of the effects of treatment of Al alloys with Sb and rare earths and may lead to improved structural controls through the use of these or other additions. In conclusion it must be remembered that Sb and its compounds give rise to health hazards, e.g. Sb can form SbH3, a toxic gas, when combined with H. . Foundries using Sb must be mindful of these dangers as well as ensuring correct separation of any Sb containing returns to avoid any contamination effects during other melt treatments. n AN INCREASE IN OVERALL ALLOY CONTENT IN Al-Si-Cu-Mg DECREASES SDAS FOR A GIVEN COOLING RATE [51,52]. ALSO, FINER SDAS ARE PRODUCED BY INCREASED SOLIDIFICATION RATE DURING SOLIDIFICATION OF A GIVEN ALLOY.
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