Abstract
Microstructure and mechanical properties development of extruded Mg-1Y (wt. %) binary alloy during equal channel angular pressing (ECAP) with route Bc at 400 °C, and subsequent annealing treatment between 300–400 °C at different holding time of 5–120 min were investigated using an optical and scanning electron microscope (SEM), electron back scattered diffraction (EBSD), tensile test, and hardness test. The grain size of as-extruded material (~10.9 μm) was refined significantly by 1-pass ECAP (~5.8 μm), and resulted in a remarkably enhanced elongation to failure (EL) (~+62%) with a slightly decreased ultimate tensile strength (UTS) (~−3%) comparing to the as-extruded condition (EL = 11.3%, UTS = 200 MPa). The EL was further increased to 27.3% (~+142%) after four passes of ECAP comparing to the as-extruded condition, which was mainly caused by the much more homogenized microstructure. The split basal poles with about 60° rotations to the extruded direction (ED), the relatively coarsened grain size by static recrystallization (SRX) and post-dynamic recrystallization (PDRX) after four passes of ECAP might be responsible for the decreased strength with increasing ECAP pass. During the annealing treatment, recovery dominantly occurred at 300 °C, SRX and grain growth emerged at 350 °C and 400 °C, respectively. Meanwhile, the grain grew and hardness decreased rapidly even within 5 min for 1-pass ECAPed material at 400 °C, indicating a larger grain boundary mobility of ECAPed materials induced by higher deformation energy than the as-extruded ones.
Highlights
Nowadays, as the problems of environment and energy shortages have become more and more serious, there is a high demand for strong and lightweight materials
After 1-pass, more and more coarse grains are substituted by fine grains and some fine grains coexist within the elongated coarse grains, which separate the elongated grains just like a stick bread cut by a knife
It is probably due to yttrium (Y) atoms segregated to the grain boundaries, which could suppress dynamic recrystallization (DRX) [21]
Summary
As the problems of environment and energy shortages have become more and more serious, there is a high demand for strong and lightweight materials. Magnesium (Mg) and its alloys are quite promising candidates due to their low density, high strength/weight ratio and cast capability [1]. The relatively low strength and ductility limit their broad applications [2]. Especially the rare earth (RE) elements, can remarkably improve the performance of magnesium [3,4]. Yttrium (Y), as a rare earth element, is widely introduced to magnesium alloys, which is capable of improving the performance of magnesium alloys more efficiently than aluminum, manganese [5] and some other RE elements [6,7]. Beyond that, during the deformation process, alloying yttrium can activate non-basal slip systems and improve the ductility of magnesium alloys [5,8,9]
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