Microstructure and Gd-rich phase evolution of as-cast AZ31- x Gd magnesium alloys during semi-solid isothermal heat trea
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Microstructure and Gd-rich phase evolution of as-cast AZ31-xGd magnesium alloys during semi-solid isothermal heat treatment CHU Chen-liang(褚晨亮)1, WU Xiao-quan(吴孝泉)1, QIU Shui-cai(邱水才)2, TANG Bin-bing(汤斌兵)3, YIN Zheng(殷正)1, YAN Hong(闫洪)1, LUO Chao(罗超)3, HU Zhi(胡志)1 1. Institute of Advanced Forming, Nanchang University, Nanchang 330031, China; 2. Changzhou University Huaide College, Jingjiang 214513, China; 3. Institute for Advanced Study, Nanchang University, Nanchang 330031, China © Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract: The microstructure and Gd-rich phase evolution of as-cast AZ31-xGd (x=0, 1.5 wt.%, 2.0 wt.% and 2.5 wt.%) magnesium alloys during semi-solid isothermal heat treatment were investigated deeply in the present work. Results showed that the lamellar (Mg,Al)3Gd phases transformed into the particle-like Al2Gd phases in AZ31 magnesium alloys with Gd addition during semi-solid isothermal heat treatment, leading to yielding more spherical α-Mg grains. When Gd content is 2.0 wt. %, the size of semi-solid spherical grains reaches the minimum. The main mechanism of grain refinement lies in the remelting of dendritic branches as well as the auxiliary effect of a small number of Al2Gd particles as grain refining inoculants. Meanwhile, Al2Gd particles enriched at the solid-liquid interfaces can remarkably retard the growth rate of α-Mg grains. A reduction of deformation resistance has been successfully achieved in AZ31-2.0Gd magnesium alloy after semi-solid isothermal heat treatment, which shows a moderate compressive deformation resistance (230 MPa), comparing to the as-cast AZ31 magnesium alloy (280 MPa) and semi-solid AZ31 magnesium alloy (209 MPa). Key words: magnesium; microstructure; rare earth element; Al2Gd particle; semi-solid isothermal heat treatment Cite this article as: CHU Chen-liang, WU Xiao-quan, QIU Shui-cai, TANG Bin-bing, YIN Zheng, YAN Hong, LUO Chao, HU Zhi. Microstructure and Gd-rich phase evolution of as-cast AZ31-xGd magnesium alloys during semi-solid isothermal heat treatment [J]. Journal of Central South University, 2020, 27. DOI: https://doi.org/10.1007/s11771-0204504-x.
1 Introduction In addition to having the lowest density (approximately 1/4 iron and 2/3 aluminum) of structural materials, Mg alloys possess advantages of a high strength-to-weight ratio, good electrical conductivity, and easy machining, leading to increasing applications in aerospace, automobiles, and 3C products [1, 2]. However, poor high-
temperature strength and plastic-forming abilities have restricted applications of these alloys. Recent studies have found that RE elements could improve the mechanical properties and thermal stability of magnesium alloys due to the precipitation strengthening, fine-grain strengthening and LPSO strengthening [3−5]. Accordingly, various LPSOcontaining Mg-RE alloys with superior mechanical properties have been developed, such as low-cost Mg88Zn4Y7 alloy and Mg96.82Gd2Zn1Zr0.18 alloy [6].
Foundation item: Project(20171
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