Microstructural Evolution of 7050 Aluminum Alloy Semisolid Billets Fabricated by RAP Process

Abstract:

In the present study, 7050 supplied in extruded state was heated to different temperatures below solidus or the semisolid state and microstructural evolution and coarsening were investigated. The results showed that complete recrystallisation only occurs after soaking for 5 minutes at 545°C, which is characterised by formation of a lot of fine equiaxed grains. RAP is suitable for fabricating high-quality semisolid billet of 7050 aluminum alloy with an average grain size ranging from 47.4 um to 70.5 um and a roundness ranging from 1.3 to 1.7. Grain growth occurs as the samples were soaked at 610°C and 615°Cfor prolonged soaking time. When the isothermal temperatures were 610°C and 615°C, the coarsening rate constants were 359.5μm3s-1 and 470.5μm3s-1, respectively, indicating an increase of coarsening rate constant (K) with the increasing isothermal temperature. Coarsening tends to occur via Ostwald ripening and coalescence. Ostwald ripening plays an important role during the whole coarsening process, but the grain coalescence only contributes to coarsening after soaking for 12 minutes. 625°C is an optimal temperature to keep cylinder shape of the sample due to collapse of the sample above this temperature, leading to difficult clamping.

• Periodical: Solid State Phenomena (Volumes 217-218)
• Pages: 29-36
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.217-218.29
• Online since: September 2014
• Authors: Ju Fu Jiang*, Zhi Ming Du, Ying Wang, Shou Jing Luo
• Keywords: 7050 Aluminum Alloy, Microstructure, RAP, Semi-Solid Billet

References

[1] D. B. Spencer. Rheology of liquid-solid mixtures of lead-tin [Ph. D Dissertation]. Cambridge, MA, USA: Massachusetts Institute of Technology; (1971).

[2] D. B. Spencer, R. Mehrabian, M. C. Flemings. Rheological behavior of Sn-15 pct Pb in the crystallization range, Metall. Trans. B 3(1972)1925-(1932).

DOI: 10.1007/bf02642580

[3] M.C. Flemings. Behavior of metal alloys in the semisolid state, Metall. Trans. B 22A(1991)957-981.

DOI: 10.1007/bf02661090

[4] S. Ji, Z. Fan, M. J. Bevis. Semi-solid processing of engineering alloys by a twin-screw rheomoulding process, Mater. Sci. Eng. A 299(2001)210-217.

DOI: 10.1016/s0921-5093(00)01373-3

[5] R. Haghayeghi, E. J. Zoqui, A. Halvaee, M. Emamy. An investigation on semi-solid Al-7Si-0. 3Mg alloy produced by mechanical stirring, J. Mater. Process. Technol. 3(2005)382-387.

DOI: 10.1016/j.jmatprotec.2005.04.071

[6] C. Vivès. Elaboration of metal matrix composites from thixotropic alloy slurries using a new magnetohydrodynamic caster. Metall. Trans. B 24b(1993)493-510.

DOI: 10.1007/bf02666433

[7] P. K. Seo, C. G. Kang, S. M. Lee. A study on reheating characteristics for thixo die casting process with electromagnetic stirring and extruded aluminum alloys and their mechanical properties, Int. J. Adv. Manuf. Technol. 43(2009)482-499.

DOI: 10.1007/s00170-008-1730-z

[8] P. Kaur, D. K. Dwivedi, P. M. Pathak. Effects of electromagnetic stirring and rare earth compounds on the microstructure and mechanical properties of hypereutectic Al–Si alloys, Int. J. Adv. Manuf. Technol. 63(2012)415-420.

DOI: 10.1007/s00170-012-3921-x

[9] K. P. Young, C. P. Kyonka, J. A. Courtois. Fine Grained metal composition, U. S . Patent 4415374. (1982).

[10] E. Parshizfard, S.G. Shabestari. An investigation on the microstructural evolution and mechanical properties of A380 aluminum alloy during SIMA process, J. Alloys Compd. 509 (2011) 9654-9658.

DOI: 10.1016/j.jallcom.2011.07.068

[11] S.Y. Lee, J.H. Lee, Y.S. Lee. Characterization of Al 7075 alloys after cold working and heating in the semi-solid temperature range, J. Mater. Process. Technol. 111(2001)42-47.

DOI: 10.1016/s0924-0136(01)00494-0

[12] D. H. Kirkwood, C. M. Sellars, L. G. Elias Boyed. Thixotropic materials. European Patent 0305375 B1 (1992).

[13] A. Bolouri, C. G. Kang. Correlation between solid fraction and tensile properties of semisolid RAP processed aluminum alloys, J. Alloys Compd. 516 (2012) 192-200.

DOI: 10.1016/j.jallcom.2012.03.062

[14] H. V. Atkinson, D. Liu. Microstructural coarsening of semi-solid aluminium alloys, Mater. Sci. Eng. A 496(2008)439-446.

DOI: 10.1016/j.msea.2008.06.013

[15] S. Chayong, H. V. Atkinson, P. Kapranos. Thixoforming 7075 aluminium alloys, Mater. Sci. Eng. A 390(2005)3-12.

DOI: 10.1016/j.msea.2004.05.004

[16] S.J. Luo, Q. Chen, Z. D. Zhao. An investigation of microstructure evolution of RAP processed ZK60 magnesium alloy, Mater. Sci. Eng. A 501 (2009) 146-152.

DOI: 10.1016/j.msea.2008.09.059

[17] Z.D. Zhao, Q. Chen, S.H. Huang, F. Kang, Y.B. Wang. Microstructure and tensile properties of AM50A magnesium alloy prepared by recrystallisation and partial melting process, Trans. Nonferrous. Met. Soc. China 20(2010)1630-1637.

DOI: 10.1016/s1003-6326(09)60350-2

[18] Y. Meng, S. Sugiyama, J. Yanagimoto. Microstructural evolution during RAP process and deformation behavior of semi-solid SKD61 tool steel, J. Mater. Process. Technol. 212 (2012) 1731-1741.

DOI: 10.1016/j.jmatprotec.2012.04.003

[19] P. K. Seo, C. G. Kang. The effect of raw material fabrication process on microstructural characteristics in reheating process for semi-solid forming, J. Mater. Process. Technol. 162-163(2005)402-409.

DOI: 10.1016/j.jmatprotec.2005.02.012

[20] I.J. Polmear, Light alloys: Metallurgy of the Light Metals, 3rd ed., Arnold, London, (1995).

[21] A. Bolouri, M. Shahmiri, C. G. Kang. Coarsening of equiaxed microstructure in the semisolid state of aluminum 7075 alloy through SIMA processing, J. Mater. Sci. 47(2012)3544-3553.

DOI: 10.1007/s10853-011-6200-6

[22] E. Tzimas, A. Zavaliangos. Evolution of near-equiaxed microstructure in the semisolid state. Mater. Sci. Eng. A 289(2000)228-240.

DOI: 10.1016/s0921-5093(00)00908-4

[23] S. Annavarapu, R. D. Doherty. Inhibited coarsening of solid-liquid microstructures in spray casting at high volume fractions of solid, Acta Metall. Mater. 43(1995)3207-3230.

DOI: 10.1016/0956-7151(94)00448-q

[24] A. Bolouri, M. Shahmiri, E. N. H. Cheshemeh. Microstructural evolution during semisolid state strain induced melt activation process of aluminum 7075 alloy, Trans. Nonferrous Met. Soc. China 20(2010)1663-1671.

DOI: 10.1016/s1003-6326(09)60355-1

[25] H. S. Kim, I. C. Stone, B. Cantor. Microstructural evolution in semi-solid AA7034, J. Mater. Sci. 43(2008)1292-1304.

DOI: 10.1007/s10853-007-2151-3

[26] A. Bolouri, M. Shahmiri, C. G. Kang. Coarsening of equiaxed microstructure in the semisolid state of aluminum 7075 alloy through SIMA processing, J. Mater. Sci. 47(2012)3544-3553.

DOI: 10.1007/s10853-011-6200-6

[27] H. Mohammadi, M. Ketabchi, A. Kalaki. Microstructure evolution of semi-solid 7075 aluminum alloy during reheating process, J. Mater. Eng. Perform. 20(2011)1256-1263.

DOI: 10.1007/s11665-010-9762-6

[28] M. Kiuchi, R. Kopp. Mushy/Semi-Solid Metal Forming Technology-Present and Future, CIRP Ann. Manuf. Techn. 51(2002)653-670.

DOI: 10.1016/s0007-8506(07)61705-3

[29] S. Ji, Z. Fan, M. J. Bevis. Semi-solid processing of engineering alloys by a twin-screw rheomoulding process, Mater. Sci. Eng. A 299(2001)210-217.

DOI: 10.1016/s0921-5093(00)01373-3