Investigation of creep behavior of ME21 and MX21 magnesium alloys

Subject Areas : journal of New Materials

Zahra Dashti ¹ , Abdolreza Geranmayeh ²

1 - Department of Materials and Metallurgy Engineering, South Tehran Branch, Islamic Azad University, Tehran ,Iran
2 - Department of Mechanical Engineering, South Tehran Branch, Islamic Azad University, Tehran ,Iran

Received: 2018-01-15 Accepted : 2019-01-31 Published : 2019-01-21

Keywords: Activation energy, Mg-Mn alloy, Impression creep, Stress exponent,

Abstract :

The creep behavior of the extruded Mg-2Mn-1Ca (MX21) and Mg-2Mn-1RE (ME21) magnesium alloys was investigated by impression testing under constant punching stress in the range 175 to 450 MPa and at temperatures in the range 423 to 498 K. Microstructural inspections with OM, SEM, EDS and XRD have proved that presence of thermally stable Mg17RE2 and Mg12RE phases in ME21 alloy and Mg2Ca phase in MX21 alloy are the main cause of enhancing the mechanical properties. For both alloys the creep behavior can be divided into two stress regimes. The stress exponents of 5 to 6 and 10 to 14 were obtained at low and high stresses, respectively. When the experimental creep rates were normalized to the pipe diffusion coefficient, however, the stress exponents of about 5-6 and 9.5-12 were obtained for the low- and high-stress regimes, respectively. The low-stress regime activation energies of about 87.1 to 92.7 kJ mol-1, which are close to 92 kJ mol-1 for dislocation-pipe diffusion in the Mg, and stress exponents in the range 4 to 6 suggest that the operative creep mechanism is dislocation climb. This behavior is in contrast to the high-stress regime, in which the stress exponents of 10 to 14 and activation energies of about 122 kJ mol-1 suggest that the operative creep mechanism is dislocation creep. The creep resistance of MX21 was only slightly lower than that of the ME21 alloy, which is attributed to formation of more thermally stable intermetallics in microstructure of ME21 alloy.

References:

References:

 

[1]  غ.ح. حسنی و ر. محمودی، "معادله بنیادی تغییرشکل گرم ورق منیزیمی Mg-4Sn-1Ca "، فصلنامه علمی-پژوهشی مواد نوین، جلد 5،  شماره 2، صفحات 10-1، سال 1393.
 
[2]  J. Wang, R. Lu, D. Qin, X. Huang, and F. Pan," A study of the ultrahigh damping capacities in Mg–Mn alloys", Materials Science and Engineering: A, Vol. 560, 2013, pp. 667-671.           

[3]  I.J. Polmear, Light Alloys, Metallurgy of light metals, 3rd ed., Amold, London, 1995.

[4]  Y.C. Lee, A.K. Dahle, and D.H. St John, "The role of solute in grain refinement of magnesium", Metallurgical and Materials Transactions A, 2000, Vol. 31, pp. 2895–2906.

[5]  Y. Lü, Q. Wang, X. Zeng, W. Ding, C. Zhai, and Y. Zhu, "Effects of rare earths on the microstructure, properties and fracture behavior of Mg–Al alloys", Materials Science and Engineering A, Vol. 278, 1999, pp. 66-76.     

[6]  W. Qudong, L. Yizhen, Z. Xiaoqin, D. Wenjiang, Z. Yanping, L. Qinghua, and L. Jie, "Study on the fluidity of AZ91+xRE magnesium alloy", Materials Science and Engineering A, Vol. 271, 1999, pp. 109-115.

[7]  B. Kondori, and R. Mahmudi, "Impression creep characteristics of a cast Mg alloy", Metallurgical and Materials Transactions A, Vol. 40A, 2009, pp. 2007–2015.

[8]  R. Mahmudi, Sh. Ansary,  and M. J. Esfandyarpour, “ Indentation creep of the wrought AZ31 magnesium alloy”, Journal of Materials Science, Vol. 47,  2012 pp. 7181–7188.

[9]      A. R. Geranmayeh, and R. Mahmudi, "Indentation creep of a cast Mg–6Al–1Zn–0.7Si alloy", Materials Science and Engineering A, Vol. 614, 2014, pp. 311-318.

[10]      A. R. Geranmayeh, and R. Mahmudi, "Compressive and impression creep behavior of a cast       Mg-Al-Zn-Si alloy", Materials Chemistry and Physics, Vol. 139, 2013, pp. 79-86.           

[11]      N. Kashefi, and R. Mahmudi, "The microstructure and impression creep behavior of cast AZ80 magnesium alloy with yttrium additions", Materials and Design, Vol. 39, 2010, pp. 200–210.  

[12]      S.N.G. Chu and J.C.M. Li, "Impression creep; a new creep test", Journal of Materials Science, Vol. 12, 1977, pp. 2200-2208.           

[13]                  J.C.M. Li, "Impression creep and other localized tests", Materials Science and Engineering A, , Vol. 322, 2002, pp. 23-42.

[14]    B.P. Zhang, L. Geng, L.J. Huang, X.X. Zhang and C.C. Dong, "Enhanced mechanical properties in fine-grained Mg-1.0Zn-0.5Ca alloys prepared by extrusion at different temperatures", Scripta Materialia, Vol. 63, 2010, pp. 1024-1027.           

[15]      I. Maxwell, and A. Hellawell, A Simple Model for Grain Refinement during Solidification, Acta Metallurgica, Vol. 23, 1975, pp. 229-237.     

[16]      F. Naghdi, and R. Mahmudi, "The microstructure and creep characteristics of cast Mg–4Zn–0.5Ca and Mg–4Zn–0.5Ca–2RE alloys", Materials Science and Engineering A, Vol. 610, 2014, 315–325.

[17]      Y. chino, M. Kobata, H. Iwasaki, and M. Mabuchi, "Tensile properties From Room Tempurture to 673 K of Mg-0.9% mass Ca Alloy containing  Lamella Mg2Ca", Materials Science,Vol. 43, 2002, pp 2643-2646.   

[18]      P. Zhang, B. Watzinger, and W. Blum, "Changes in microstructure and deformation resistance during creep of the die-cast Mg-Al-Base alloy AZ91hp at intermediate temperatures up to 150", Physica Status Solidi A, Vol. 175, 1999, pp. 481-487.

[19]      T.G. Langdon, "Identifiying creep mechanisms at low stresses", Materials Science and Engineering A, Vol. 283, 2000, pp. 266–273.        

[20]      S. Takeochi, and A.S. Argon, "Review, steady-state creep of single-phase crystalline matter at high temperature", Journal of Materials Science, Vol. 11, 1976, pp. 1542-1566. 

[21]      O.D. Sherby, and E.M. Taleff, "Influence of grain size, solute atoms and second-phase particles on creep behavior of polycrystalline solids", Materials Science and Engineering A, Vol. 322, 2002, pp. 89–99.

[22]      O.D. Sherby, and P.M. Burke, "Mechanical behavior of crystalline solids at elevated temperature", Progress in Materials Science, 1968, Vol. 13, pp. 323-390.

[23]      F.A. Mohamed, and T.G. Langdon, "The transition from dislocation climb to viscous glide in creep of solid solution alloys",  Vol. 22, 1974, pp. 779-788.           

[24]      P. Yavari, and T.G. Langdon, "An examination of the breakdown in the creep by viscous glide in solid solution alloys at high stress levels",  Vol. 30, 1982, pp. 2181-2196.

[25]      S.V. Raj, "Power-law and exponential creep in class M materials: discrepancies in experimental observations and implications for creep modeling", Materials Science and Engineering A, Vol.  322, 2002, pp. 132-147.            

[26]      T. Reinikainem, and J. Kivilahti, "Deformation behavior of dilute SnBi(0.5 to 6 at. Pct) solid", Metallurgical and Materials Transactions A, Vol. 30, 1999, pp. 123-132.