Evolution of Microstructure and Mechanical Properties of the Thixo-Diecast 319s Alloy during Heat Treatment

Abstract:

The evolution of microstructure and mechanical properties during solution and ageing heat treatment process was studied in terms of a thixo-diecast impeller of 319s aluminium alloy. The cast alloy exhibited a microstructure consisting of primary uniformly distributed in α-Al globules and the eutectics. A series of heat treatment studies were performed to determine optimum heat treatment parameters, in order to achieve fine grain structure, fine silicon particles and optimal precipitate size and distribution. Optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to study the evolution of microstructure and mechanical properties. The results demonstrate that, the full T6 heat treatments are successfully applied to thixo-diecast 319s impellers. A two-step solution heat treatment is employed to prevent porosity due to overheating. The tensile properties of thixo-diecast 319s impellers were substantially enhanced after T6 heat treatment. The plate-shaped θ′ precipitates and lath-shaped Q′ precipitates are the most effective for precipitation strengthening.

• Periodical: Materials Science Forum (Volume 765)
• Pages: 511-515
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.765.511
• Online since: July 2013
• Authors: Da Quan Li, Xiao Kang Liang, Fu Bao Yang, You Feng He, Fan Zhang, Qiang Zhu, Shao Ming Zhang
• Keywords: Alloy 319s, Heat Treatment, Thixo-Diecast

References

[1] Q. Zhu, S.P. Midson, Semi-solid moulding: a competition to cast and machine from forging in making automotive complex components, Trans. Nonferrous Met. Soc. China. 20 (2010) s1042-s1047.

DOI: 10.1016/s1003-6326(10)60628-0

[2] G. Wallace, A.P. Jackson, S.P. Midson, Q. Zhu, High-quality aluminum turbocharger impellers produced by thixocasting, Trans. Nonferrous Met. Soc. China. 20 (2010) s1786-s1791.

DOI: 10.1016/s1003-6326(09)60375-7

[3] E. Sjolander, S. Seifeddine, The heat treatment of Al-Si-Cu-Mg casting alloys, J. Mater. Process. Technol. 210 (2010) 1249-1259.

DOI: 10.1016/j.jmatprotec.2010.03.020

[4] A.M.A. Mohamed, F.H. Samuel, S. Alkahtani, Influence of Mg and solution heat treatment on the occurrence of incipient melting in Al-Si-Cu-Mg cast alloys, Mat. Sci. Eng. A 543 (2012) 22-34.

DOI: 10.1016/j.msea.2012.02.032

[5] J.Y. Hwang, R. Banerjee, H.W. Doty, M.J. Kaufman, The effect of Mg on the structure and properties of type 319 aluminum casting alloys, Acta Mater. 57 (2009) 1308-1317.

DOI: 10.1016/j.actamat.2008.11.021

[6] M. Tash, F.H. Samuel, F. Mucciardi, H.W. Doty, Effect of metallurgical parameters on the hardness and microstructural characterization of as-cast and heat-treated 356 and 319 aluminum alloys, Mat. Sci. Eng. A 443 (2007) 185-201.

DOI: 10.1016/j.msea.2006.08.054

[7] F.J. Tavitas-Medrano, J.E. Gruzleski, F.H. Samuel, S. Valtierra, H.W. Doty, Effect of Mg and Sr-modification on the mechanical properties of 319-type aluminum cast alloys subjected to artificial aging, Mat. Sci. Eng. A 480 (2008) 356-364.

DOI: 10.1016/j.msea.2007.09.002

[8] M.F. Ibrahim, E. Samuel, A.M. Samuel, A.M.A. Al-Ahmari, F.H. Samuel, Impact toughness and fractography of Al-Si-Cu-Mg base alloys, Mater. Des. 32 (2011) 3900-3910.

DOI: 10.1016/j.matdes.2011.02.058

[9] M.F. Ibrahim, E. Samuel, A.M. Samuel, A.M.A. Al-Ahmari, F.H. Samuel, Metallurgical parameters controlling the microstructure and hardness of Al-Si-Cu-Mg base alloys, Mater. Des. 32 (2011) 2130-2142.

DOI: 10.1016/j.matdes.2010.11.040

[10] S.G. Shabestari, M. Malekan, Assessment of the effect of grain refinement on the solidification characteristics of 319 aluminum alloy using thermal analysis, J. Alloy Compd. 492 (2010) 134-142.

DOI: 10.1016/j.jallcom.2009.11.122

[11] F.C. Robles Hernandez, J.H. Sokolowski, Effects and on-line prediction of electromagnetic stirring on microstructure refinement of the 319 Al-Si hypoeutectic alloy, J. Alloy Compd. 480 (2009) 416-421.

DOI: 10.1016/j.jallcom.2009.02.109

[12] J.A. Taylor, Iron-containing intermetallic phases in Al-Si based casting alloys, Procedia Mater. Sci. 1 (2012) 19-33.

DOI: 10.1016/j.mspro.2012.06.004

[13] X. Pan, J.E. Morral, H.D. Brody, Predicting the Q-phase in Al-Cu-Mg-Si alloys, J. Phase Equilib. Diff. 31 (2010) 144-148.

DOI: 10.1007/s11669-009-9640-9