Abstract
Although body-centered cubic (BCC) structural magnesium–lithium (Mg-Li) alloys have lower density and better formability than common hexagonal close-packed (HCP) Mg alloys, their applications remain limited due to their low strength. The purpose of this study is to investigate the effect of Y/Er and Zn addition on the microstructure and tensile properties of Mg-11Li alloy with a BCC structural matrix by comparing Mg-11Li, Mg-11Li-4Y-2Er-2Zn, and Mg-11Li-8Y-4Er-4Zn (wt %) alloys. The results indicate that the addition of Y/Er and Zn at a ratio of 3:1 cannot promote the formation of long-period stacking ordered structure in Mg-11Li alloy such as that in Mg-Y-Er-Zn alloys and the dominant intermetallic phases formed are BCC Mg24RE5 and face-centered cubic (FCC) Mg3RE2Zn3 phases. With an increase of the content of Y/Er and Zn in an as-cast alloy, the fraction of intermetallic particles increases and the grain size decreases. The addition of Y/Er, as well as Zn, dramatically promotes the refinement of dynamic recrystallization (DRX) during extrusion. The initial intermetallic phases induced by Y/Er and Zn addition are broken into relatively fine particles during extrusion, and this contributes to refining the dynamic recrystallized (DRXed) grains mainly by the particle stimulated nucleation mechanism. The as-extruded Mg-11Li-4Y-2Er-2Zn and Mg-11Li-8Y-4Er-4Zn alloys exhibit much higher tensile strength as compared with as-extruded Mg-11Li alloy, which is mainly ascribed to the refined DRXed grains and numerous dispersed intermetallic phase particles. It is suggested that further refinement of intermetallic particles in these extruded Mg-11Li-based alloys may lead to higher quality alloy materials with low density and excellent mechanical properties.
Highlights
Magnesium (Mg) alloys, as lightweight structural metallic materials, have great potential in automotive and aerospace applications [1,2,3,4], some inherent weaknesses, such as poor formability at room temperature owing to the limited slip systems in the hexagonal close-packed (HCP)Materials 2019, 12, 3066; doi:10.3390/ma12193066 www.mdpi.com/journal/materialsMaterials 2019, 12, 3066 structure, restrict their applications [5,6]
The crystal structure of Mg-Li alloys change from an α (HCP) structure of Mg solid solution to a β (BCC) structure of Li solid solution when the amount of the Li added in Mg exceeds ~11 wt % [7,8], which can significantly improve the formability by providing more slip systems at room temperature [9,10,11,12]
The effect of Y/Er and Zn addition on the microstructure and tensile properties of Mg-11Li alloy with body-centered cubic (BCC) structural matrix was investigated by the comparison of Mg-11Li, Mg-11Li–4Y-2Er-2Zn, and Mg-11Li-8Y-4Er-4Zn alloys, and the main conclusions are listed as follows: (1) The addition of Y/Er and Zn at the ratio of 3:1 to Mg-11Li alloy does not promote the formation of long-period stacking ordered (LPSO) structure such as that in Mg-Y-Er-Zn alloys, and the dominant intermetallic phases formed are BCC Mg24 RE5 and face-centered cubic (FCC) W phases
Summary
Magnesium (Mg) alloys, as lightweight structural metallic materials, have great potential in automotive and aerospace applications [1,2,3,4], some inherent weaknesses, such as poor formability at room temperature owing to the limited slip systems in the hexagonal close-packed (HCP)Materials 2019, 12, 3066; doi:10.3390/ma12193066 www.mdpi.com/journal/materialsMaterials 2019, 12, 3066 structure, restrict their applications [5,6]. The ultimate tensile strength (UTS) of common Mg-Li alloys containing high Li content is rarely more than 200 MPa even after severe plastic deformation (equal channel angular extrusion or hot extrusion) [13,14,15,16], which is not conducive to the wide application of Mg alloys. At present, it is well-known that the addition of rare earth (RE) can effectively enhance the strength and heat resistance of Mg alloys, forming typical Mg–RE series and Mg–RE–Zn series alloys [17,18,19,20,21]. The influence of RE combined with Zn on some
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
