J. Mater. Sci. Technol. ›› 2018, Vol. 34 ›› Issue (7): 1110-1118.DOI: 10.1016/j.jmst.2017.12.005

• Orginal Article • Previous Articles     Next Articles

Strengthening mechanisms in magnesium alloys containing ternary I, W and LPSO phases

N. Tahreena, D.F. Zhangbc, F.S. Panbcd, X.Q. Jiangde, D.Y. Lif, D.L. Chena()   

  1. aDepartment of Mechanical and Industrial Engineering, Ryerson University, Toronto, Ontario, M5B 2K3, Canada
    bCollege of Materials Science and Engineering, Chongqing University, Chongqing, 400045, China
    cNational Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing, 400044, China
    dAdvanced Materials Research Center, Chongqing Academy of Science and Technology, Chongqing, 401123, China
    eFaculty of Materials and Energy, Southwest University, Chongqing, 400715, China
    fDepartment of Chemical and Materials Engineering, University of Alberta, Alberta, T6G 1H9, Canada
  • Received:2017-10-05 Revised:2017-11-29 Accepted:2017-11-30 Online:2018-07-10 Published:2018-07-22

Abstract:

This study was aimed at identifying underlying strengthening mechanisms and predicting the yield strength of as-extruded Mg-Zn-Y alloys with varying amounts of yttrium (Y) element. The addition of Y resulted in the formation of ternary I (Mg3YZn6), W (Mg3Y2Zn3) and LPSO (Mg12YZn) phases which subsequently reinforced alloys ZM31 + 0.3Y, ZM31 + 3.2Y and ZM31 + 6Y, where the value denoted the amount of Y element (in wt%). Yield strength of the alloys was determined via uniaxial compression testing, and grain size and second-phase particles were characterized using OM and SEM. In-situ high-temperature XRD was performed to determine the coefficient of thermal expansion (CTE), which was derived to be 1.38 × 10-5 K-1 and 2.35 × 10-5 K-1 for W and LPSO phases, respectively. The individual strengthening effects in each material were quantified for the first time, including grain refinement, Orowan looping, thermal mismatch, dislocation density, load-bearing, and particle shearing contributions. Grain refinement was one of the major strengthening mechanisms and it was present in all the alloys studied, irrespective of the second-phase particles. Orowan looping and CTE mismatch were the predominant strengthening mechanisms in the ZM31 + 0.3Y and ZM31 + 3.2Y alloys containing I and W phases, respectively, while load-bearing and second-phase shearing were the salient mechanisms contributing largely to the superior yield strength of the LPSO-reinforced ZM31 + 6Y alloy.

Key words: Magnesium alloy, I-phase, W-phase, LPSO phase, Strengthening mechanism