Microstructure and Mechanical Properties of a Fine-Grained AZ91 Magnesium Alloy Prepared by Multi-Pass Friction Stir Processing

Abstract:

Friction stir processing (FSP) is a novel severe plastic deformation technique developed in recent years to produce fine-grained structural materials. Through increasing the processing pass, further grain refinement can be achieved. In this paper, the microstructure and mechanical properties of AZ91 magnesium alloy prepared by the single-pass and two-pass FSP were studied. The results showed that the coarse, network-like eutectic β-Mg₁₇Al₁₂ phase was broken into particles and some of them dissolved into the magnesium matrix, and the α-Mg grains were remarkably refined after FSP. The average grain sizes of the single-pass and two-pass FSP alloys were 8.3 μm and 5.8 μm respectively. The ultimate tensile strengths of the specimens were 284.5 MPa and 319.7 MPa, and elongations were 13% and 14.5%, respectively. The improved mechanical properties of the two-pass FSP specimen were mainly attributed to the finer grain size and more homogenized microstructure.

• Periodical: Materials Science Forum (Volume 850)
• Pages: 778-783
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.850.778
• Online since: March 2016
• Authors: Zhi Long Lu, Da Tong Zhang
• Keywords: AZ91 Magnesium Alloy, Friction Stir Processing, Mechanical Properties, Microstructure

References

[1] B.L. Mordike, T. Ebert, Magnesium Properties-applications-potential. Materials Science and Engineering A[J], 2001. 302: 37-45.

[2] R.S. Mishra, Z.Y. Ma. Friction stir welding and processing. Materials Science and Engineering: R: Reports[J], 2005. 50(1-2): 1-78.

[3] F.C. Liu, Z.Y. Ma, L.Q. Chen. Low-temperature superplasticity of Al–Mg–Sc alloy produced by friction stir processing. Scripta Materialia[J], 2009. 60(11): 968-971.

DOI: 10.1016/j.scriptamat.2009.02.021

[4] Z.Y. Ma, S.R. Sharma, R.S. Mishra, Effect of friction stir processing on the microstructure of cast A356 aluminum. Materials Science and Engineering: A[J], 2006. 433(1-2): 269-278.

DOI: 10.1016/j.msea.2006.06.099

[5] T. Morishige, T. Hirata, T. Uesugi, Y. Takigawa, M. Tsujikawa, K. Higashi. Effect of Mg content on the minimum grain size of Al–Mg alloys obtained by friction stir processing. Scripta Materialia[J], 2011. 64(4): pp.355-358.

DOI: 10.1016/j.scriptamat.2010.10.033

[6] X. Feng, H. Liu, S. Suresh Babu. Effect of grain size refinement and precipitation reactions on strengthening in friction stir processed Al–Cu alloys. Scripta Materialia[J], 2011. 65(12): 1057-1060.

DOI: 10.1016/j.scriptamat.2011.09.009

[7] A. Kurt, I. Uygur, E. Cete. Surface modification of aluminium by friction stir processing. Journal of Materials Processing Technology[J], 2011. 211(3): 313-317.

DOI: 10.1016/j.jmatprotec.2010.09.020

[8] A.H. Feng, Z.Y. Ma, Enhanced mechanical properties of Mg–Al–Zn cast alloy via friction stir processing. Scripta Materialia[J], 2007. 56(5): 397-400.

DOI: 10.1016/j.scriptamat.2006.10.035

[9] L. Commin, M. Dumont, J. -E. Masse, L. Barrallier. Friction stir welding of AZ31 magnesium alloy rolled sheets: Influence of processing parameters. Acta Materialia[J], 2009. 57(2): 326-334.

DOI: 10.1016/j.actamat.2008.09.011

[10] D.R. Ni, D. Wang, A.H. Feng, G. Yao, Z.Y. Ma. Enhancing the high-cycle fatigue strength of Mg–9Al–1Zn casting by friction stir processing. Scripta Materialia[J], 2009. 61(6): 568-571.

DOI: 10.1016/j.scriptamat.2009.05.023

[11] Y.N. Wang, C.I. Chang, C.J. Lee, H.K. Lin, J.C. Huang. Texture and weak grain size dependence in friction stir processed Mg–Al–Zn alloy. Scripta Materialia[J], 2006. 55(7): 637-640.

DOI: 10.1016/j.scriptamat.2006.06.005

[12] C.I. Chang, X.H. Du, J.C. Huang. Achieving ultrafine grain size in Mg–Al–Zn alloy by friction stir processing. Scripta Materialia[J], 2007. 57(3): 209-212.

DOI: 10.1016/j.scriptamat.2007.04.007

[13] W. Wang, K.S. Wang,Q. Guo. Effect of Friction Stir Processing on Microstructure and Mechanical Properties of Cast AZ31 Magnesium Alloy. Rare Metal Materials and Engineering [J] , 2012, 41(9): 1522-1526.

DOI: 10.1016/s1875-5372(13)60004-1

[14] C.I. Chang, C.J. Lee, J.C. Huang. Relationship between grain size and Zener–Holloman parameter during friction stir processing in AZ31 Mg alloys. Scripta Materialia[J], 2004 51: 509-514.

DOI: 10.1016/j.scriptamat.2004.05.043

[15] Z.Y. Ma, A.L. Pilchak, M.C. Juhasb, J.C. Williams. Microstructural refinement and property enhancement of cast lightalloys via friction stir processing. Scripta Materialia[J], 2008 58 : 361-366.

DOI: 10.1016/j.scriptamat.2007.09.062