Formation Behavior of 14H Long Period Stacking Ordered Structure in Mg-Y-Zn Cast Alloys with Different ~-Mg Fractions

• Published in: 材料科学技术学报：英文版 2016, Vol.32 (12), p.1267-1273
• Main Author: Huan Liu Feng Xue Jing Bai Aibin Ma Jinghua Jiang
• Format: Article
• Language: English
• Subjects: 体积分数; 合金; 显微组织; 有序; 构形; 行为; 退火温度; 长周期
• ISSN: 1005-0302; 1941-1162

Phase compositions and microstructure evolutions of three Mg-Y-Zn cast alloys during isothermal annealing at 773 K have been systematically investigated to clarify the formation behavior of 14 H long period stacking ordered（LPSO） structure from α-Mg grains.The annealed microstructure characteristics indicate that the 18 R phase is thermal stable in Mg86Y8Zn6 alloy where 18 R serves as matrix,and 14 H lamellar phase only forms within tiny α-Mg slices（less than 1% for volume fraction）.The α-Mg grains in Mg88Y8Zn4 and Mg89Y8Zn3 alloys exhibit cellular shape,and 14 H phase forms and develops into lamellar shape in these cellular grains after annealing.The results suggest that the presence of α-Mg grains is a requirement for the generation of 14 H phase.The nucleation and growth rates of 14 H lamellas are accelerated in α-Mg grains with higher concentrations of stacking faults and solute atoms.Moreover,the 14 H lamellas are parallel to adjacent 18 R plates in Mg86Y8Zn6 alloy,but the 14 H phase precipitated in cellularα-Mg grains of Mg88Y8Zn4 and Mg89Y8Zn3 alloys exhibits random orientation relationship with surrounding 18 R phase,indicating that the orientation relationship between 14 H and 18 R phases depends on the relationship between α-Mg grains and 18 R phase.