Abstract
The thixoforming process is a new method for manufacturing complicated and net shape components through which high strength materials can be formed more easily. In this study 7075 Al alloy which has low extrudability has been thixoformed by backward extrusion process. The recrystallisation and partial melting (RAP) route was used to obtain the semi-solid feedstocks for thixoforming. Microstructural evolution during partial remelting was studied at temperatures for times. Results showed that a fine and globular microstructure can be obtained by the RAP route. The results showed that high semisolid isothermal temperature would increase the liquid volume fraction and accelerate the spherical processing of the solid particles. Furthermore at long holding time, the globular grains coarsened slightly and the average grains size are increased. The experimental results showed that when the semisolid billet is hold at 580°C with the holding time, less than 30 min, the microstructure of the billet is composed of spherical grains and remnant liquids, the average grain size are smaller than 100 μm. So the remelted billet is suitable for thixoforming. In this paper, a back-extruding of 7075 Al alloy with a high solid fraction in the semi-solid state at 580°C for 10 min was performed. Mechanical properties of thixoformed components at room temperature were examined. Tempering treatment T6 has been applied after thixoforming to investigate the effects of heat treatment on mechanical properties of thixoformed parts. The tensile properties and low hardness values in the as-thixoformed 7075 Al alloy were improved by subsequent heat treatment. Post-forming heat treatment is one of the key parameters for improving the mechanical properties of thixoformed parts.
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References
Jiang H, Li M (2005) Microscopic observation of cold-deformed Al–4 Cu–Mg alloy samples after semi-solid heat treatments. Mater Charact 54:451–457. doi:10.1016/j.matchar.2005.01.010
Fan Z (2002) Semi-solid metal processing. Int Mater Rev 47:67. doi:10.1179/095066001225001076
Atkinson HV, Burke K, Vaneetveld G (2008) Recrystallisation in the semi-solid state in 7075 aluminium alloy. Mater Sci Eng, A 490:266–276. doi:10.1016/j.msea.2008.01.057
Chayong S, Atkinson HV, Kapranos P (2005) Thixoforming 7075 aluminum alloys. Mater Sci Eng, A 390:3–12. doi:10.1016/j.msea.2004.05.004
Dong J, Cui JZ, Le QC, Lu GM (2003) Liquidus semi-continuous casting, reheating and thixoforming of a wrought aluminum alloy 7075. Mater Sci Eng, A 345:234–242
Sang-Yong L, Jung-Hwan L, Young-Seon L (2001) Characterization of Al 7075 alloys after cold working and heating in the semi-solid temperature range. Mater Process Technol 111:42–47
Zhang L, Liu YB, Cao ZY et al (2009) Effects of isothermal process parameters on the microstructure of semi-solid AZ91D alloy produced by SIMA. Mater Process Technol 209:792–797. doi:10.1016/j.jmatprotec.2008.02.046
Becker E, Bigot R, Langlois L et al (2008) Metallurgical and mechanical analysis from thixoforging steel shape. Int J Mater Form Suppl 1:977–980. doi:10.1007/s12289-008-0221-y
Rovira MM, Lancini BC, Robert MH (1999) Thixo-forming of Al–Cu alloys. Mater Process Technol 92–93:42–49
Zhao Z, Chen Q, Chao H, Huang S (2010) Microstructural evolution and tensile mechanical properties of thixoforged ZK60-Y magnesium alloys produced by two different routes. Mater Des 31:1906–1916. doi:10.1016/j.matdes.2009.10.056
Birol Y (2008) Thixoforging experiments with 6082 extrusion feedstock. Alloy Comp 455:178–185. doi:10.1016/j.jallcom.2007.01.053
Hong-min G, Xiang-jie Y, Meng Z (2008) Microstructure characteristics and mechanical properties of rheoformed wrought aluminum alloy 2024. Trans Nonferrous Met Soc China 18:555–561
Tahamtan S, Golozar MA, Karimzadeh F, Niroumand B (2008) Microstructure and tensile properties of thixoformed A356 alloy. Mater Charact 59:223–228. doi:10.1016/j.matchar.2006.12.010
ASTM E-8 M. Standard test methods for tension testing of metallic materials [Metric]. ASTM international
Favier V, Cézard P, Bigot R (2009) Transient and non-isothermal semi-solid behaviour: 3D micromechanical modeling. Mater Sci Eng, A 517:8–16. doi:10.1016/j.msea.2009.03.018
Atkinson HV, Burke K, Vaneetveld G (2008) Recrystallisation in the Semi-Solid State in 7075 Aluminium Alloy. Int J Mater Form Suppl 1:973–976. doi:10.1007/s12289-008-0220z
Ji Z, Hu M, Sugiyama S, Yanagimoto J (2008) Formation process of AZ31B semi-solid microstructures through strain-induced melt activation method. Mater Charact 59:905–911. doi:10.1016/j.matchar.2007.07.015
Moradi M, Nili-Ahmadabadi M, Poorganji B et al (2010) Recrystallization behavior of ECAPed A356 alloy at semi-solid reheating temperature. Mater Sci Eng, A 527:4113–4121. doi:10.1016/j.msea.2010.03.021
Hirt G et al (2009) Thixoforming: Semi-solid metal processing. Wiley Publication
Jufu J, Ying W, Jianjun Q et al (2010) Microstructure evolution of AM60 magnesium alloy semisolid slurry prepared by new SIMA. J Alloy Comp 497:62–67. doi:10.1016/j.jallcom.2010.02.099
Tzimas E, Zavaliangos A (2000) Evolution of near-equiaxed microstructure in the semisolid state. Mater Sci Eng, A 289:228–240
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Mohammadi, H., Ketabchi, M. & Kalaki, A. Microstructural evolution and mechanical properties of back-extruded Al 7075 alloy in the semi-solid state. Int J Mater Form 5, 109–119 (2012). https://doi.org/10.1007/s12289-010-1022-7
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DOI: https://doi.org/10.1007/s12289-010-1022-7