Influence of various Yb additions on microstructures of a casting Mg−8Gd−1.2Zn−0.5Zr alloy

• Published in: Journal of alloys and compounds Vol. 789; pp. 720 - 729
• Main Authors: Li, Baishun, Meng, Fanzhi, Lv, Shuhui, Guan, Kai, Yang, Qiang, Qin, Pengfei, Qiu, Xin, Tian, Zheng, Zhang, Dongdong, Meng, Jian
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.06.2019; Elsevier BV
• Subjects: Alloys; Eutectic alloys; Eutectics; Gadolinium; Grain boundaries; Intermetallic phase; Intermetallic phases; Magnesium alloy; Orientation relationships; Permanent mold casting; Permanent molds; Transmission electron microscopy (TEM); Yb addition; Ytterbium; Yb addition; Intermetallic phase; Transmission electron microscopy (TEM); Magnesium alloy
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2019.03.104

Microstructures of the Mg−8Gd−xYb−1.2Zn−0.5Zr (x = 0, 1, 2, 3, and 4, in wt.%) alloys prepared by gravity permanent mold casting were investigated. The results indicate that the components of intermetallic phases are closely depended on the content of Yb additions. Firstly, the eutectic phase in the alloy with free Yb addition is Mg3Gd. As the Yb addition increases, Mg5(Gd,Yb) and Mg12(Gd,Yb) eutectic phases successively formed. Furthermore, both Mg5(Gd,Yb) and Mg12(Gd,Yb) are coherent with Mg3(Gd,Yb) following orientation relationships (ORs) as: (200)Mg3(Gd,Yb)//(200)Mg5(Gd,Yb), [001]Mg3(Gd,Yb)//[001]Mg5(Gd,Yb), and (002)Mg3(Gd,Yb)//(006)Mg12(Gd,Yb), [010]Mg3(Gd,Yb)//[010]Mg12(Gd,Yb), respectively. Then, the volume fractions of Mg5(Gd,Yb) and Mg12(Gd,Yb) gradually increase as the Yb content increases. When the Yb addition is over 3 wt.%, the Mg5(Gd,Yb) phase becomes the dominant eutectic phase. Finally, the volume fraction of 14H-type long-period stacking ordered (LPSO) phase which mainly distributes in the regions near grain boundaries clearly decreases as the Yb content increases. •Microstructure evolutions of Mg−8Gd−xYb−1.2Zn−0.5Zr alloys were investigated.•Mg5(Gd,Yb) and Mg12(Gd,Yb) phases successively formed as the Yb content increases.•Both Mg5(Gd,Yb) and Mg12(Gd,Yb) coexist with and are coherent with Mg3(Gd,Yb).•As Yb addition increases, the volume fraction of Mg5(Gd,Yb) and Mg12(Gd,Yb) increases.•The volume fraction of Mg3(Gd,Yb) and LPSO phase decreases as Yb addition increases.