LPSO STRUCTURE AND AGING PHASES IN Mg-Gd-Zn-Zr ALLOY

ZENG Xiao-Qi; WU Yu-Juan; PENG Li-Meng; LIN Dong-Liang; DING Wen-Jiang

doi:10.3724/SP.J.1037.2009.00833

Acta Metall Sin >

2010 , Vol. 46 >Issue 9: 1041 - 1046

DOI: https://doi.org/10.3724/SP.J.1037.2009.00833

论文

LPSO STRUCTURE AND AGING PHASES IN Mg-Gd-Zn-Zr ALLOY

ZENG Xiao-Qi ,
WU Yu-Juan ,
PENG Li-Meng ,
LIN Dong-Liang ,
DING Wen-Jiang

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1) National Engineering Research Center of Light Alloy Net Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240
2) The State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240
3) School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240

Received date: 2009-12-14

Revised date: 2010-06-16

Online published: 2010-09-11

Supported by

Supported by National Natural Science Foundation of China (No.50971089), Science and Technology Commission of Shanghai Municipality (No.08JC1412200) and China Postdoctoral Science Foundation (No.20090460615)

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Abstract

At present, long period stacking ordered (LPSO) structures in Mg-RE-Zn (RE=Y, Dy, Ho, Er, Gd, Tb, Tm) alloys have been focused on. According to some reports, Mg-Gd-Zn alloys are classified as type II, i.e., there are no LPSO structures in as-cast alloys, but LPSO structures appear after heat treatment. To further study the formation of LPSO structure in Mg-Gd-Zn(Zr)\linebreak alloys, a Mg_96.32Gd_2.50Zn_1.00Zr_0.18 alloy was prepared by ingot metallurgy (I/M) in this work. Based on OM, SEM and TEM observations, the as-cast microstructure of Mg-Gd-Zn-Zr alloy consists of α-Mg solid solution, lamellar 14H-type LPSO structure within α-Mg grains and dendritic eutectic structure at grain boundaries, in which the eutectic phase is the β-phase ((Mg, Zn)₃Gd)), thus, Mg-Gd-Zn(Zr) alloys should be attributed to type I, i.e., there are LPSO structures in as-cast alloys. During solid solution treatment at 500 ℃ for 35 h, a solid transformation, dendritic β-phase with fcc structure→lamellar X-phase with 14H structure, was observed at grain boundaries. During subsequent peak-aging treatment at 200 ℃ for 128 h, ellipsoidal β´ and rhombus β₁ phases precipitated within α-Mg grains. Tensile tests at room temperature and Vickers hardness tests show that the alloy solution-treated and aging-treated has higher mechanical properties, i.e., σ_b=290.7 MPa, σ_s=162.5 MPa, δ=10.35% and 108.0 HV. The improvement of mechanical properties are attributed to the composite strengthening-and-toughening effect of the 14H-type LPSO structures, and the β´ and β₁aging phases.

Key words： Mg-Gd-Zn-Zr alloy; long period stacking ordered (LPSO) structure; lamellar; aging treatment

Cite this article

ZENG Xiao-Qi , WU Yu-Juan , PENG Li-Meng , LIN Dong-Liang , DING Wen-Jiang . LPSO STRUCTURE AND AGING PHASES IN Mg-Gd-Zn-Zr ALLOY[J]. Acta Metall Sin, 2010 , 46(9) : 1041 -1046 . DOI: 10.3724/SP.J.1037.2009.00833

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