Microstructures and mechanical properties of a hot-extruded Mg-8Ho-0.6Zn-0.5Zr alloy

The microstructures and mechanical properties of a Mg-8Ho-0.6Zn-0.5Zr alloy were thoroughly investigated. The results reveal five kinds of intermetallic phases, namely the 14H long-period stacking ordered (LPSO) phase, the 18R LPSO phase, Mg24Ho5, Mg0.5Ho1.5, and Mg3Ho. Ordinarily, the 18R LPSO phase locates at a lamellae grain boundary with the misorientation angle of 136.9 degrees and is simultaneously coherent with two alpha-Mg grains. The corresponding orientation relationships are as (001)(18R)//(0001)(alpha 1) and [010](18R)//11 (2) over bar0)(alpha 1), and (001)(18R) about 43.1 degrees from (0001)(alpha 2) and [010](18R) //< 11 (2) over bar0 >(alpha 2). After hotextrusion, the disintegrated intermetallic phases composed of Mg24Ho5 and Mg3Ho mainly distribute at extrusion stringers while the LPSO phases mainly locate in un-recrystallized regions. In addition, amounts of fine spherical intermetallic particles were formed when many parallelly distributed LPSO plates precipitated in a part of the recrystallized grains. The as-extruded Mg-8Ho-0.6Zn-0.5Zr alloy exhibits excellent combination of high strength and high ductility. The underlying strengthening mechanisms were revealed as fine-grain strengthening and dispersion strengthening. (C) 2018 Elsevier B.V. All rights reserved.