12th International Conference on Magnesium Alloys and their Applications (Mg 2021): LPSO & MFS Structures IV
Program Organizers: Alan Luo, Ohio State University; Mihriban Pekguleryuz, McGill University; Sean Agnew, University of Virginia; John Allison, University of Michigan; Karl Kainer; Eric Nyberg, Kaiser Aluminum Trentwood; Warren Poole, University of British Columbia; Kumar Sadayappan, CanmetMATERIALS; Bruce Williams, Canmetmaterials Natural Resources Canada; Stephen Yue, Mcgill University
Friday 10:50 AM
June 18, 2021
Room: Contributed IV
Location: Virtual
Session Chair: Hiroshi Okuda, Kyoto University
Effects of Pre-straining and Heat Treatment on Room Temperature and Creep Strength in a Long Period Stacking Ordered Type Mg-Zn-Y Alloy: Mayumi Suzuki1; Tatsuya Yamaguchi1; Koji Hagihara2; 1Toyama Prefectural University; 2Osaka University
Long period stacking ordered (LPSO) type magnesium alloys have been investigated by many researchers because of their excellent mechanical properties and unique crystalline structures. In the present investigation, the effects of kink density and subsequent heat treatment have been investigated on compression strength in a directionally solidified (DS) Mg-Y-Zn based LPSO alloys.Kink boundaries were introduced heterogeneously in DS alloys and many dislocations are introduced within grains after room temperature pre-straining. Both of room temperature compression strength and creep strength increases with increasing the value of the pre-strain. Mechanical properties of pre-strained specimens improved by high temperature heat treatment at 750 K, whereas their strength was decreased by the heat treatment at 650 K. EBSD analysis revealed that some recovery/re-arrangement of kink bands were occurred during heat treatment at 750 K. This microstructural change was affected significantly by both of kink density and subsequent heat treatment conditions.
Tensile Strengthening of a Mg Alloy Containing 25-vol% LPSO by Hot Extrusion Revealed by Neutron Diffraction: Stefanus Harjo1; Wu Gong2; Kazuya Aizawa1; Takuro Kawasaki1; Michiaki Yamasaki3; Yoshihito Kawamura3; 1Japan Atomic Energy Agency; 2Kyoto University; 3Kumamoto University
Interesting mechanical properties changes were found in Mg97Zn1Y2 alloy containing about 25-vol% long-period stacking ordered phase (LPSO) in the HCP structured α matrix (αMg), by hot-extrusion. In situ neutron diffraction measurements during tensile loading were conducted on three Mg97Zn1Y2 alloys with different processes: as-casted, and after hot-extrusion at 623 K with extrusion ratios of 5.0 and 12.5, to elucidate the relation between the changes in microstructure by hot-extrusion with the changes in mechanical property. The yield strength of αMg increased by the hot-extrusion, but when the extrusion ratio increased the αMg yield strength ironically decreased. LPSO was found to be strengthened monotonically as the extrusion ratio increased. Detailed results of neutron diffraction will be discussed to explain the mechanical properties changes of Mg97Zn1Y2 alloy by hot-extrusion.
Mechanical Properties of Hot-compressed Mg-Y-Zn Alloys with LPSO Phase: Yuto Nakasuji1; Motohiro Yuasa1; Hiroyuki Miyamoto1; Hidetoshi Somekawa2; 1Doshisha University; 2National Institute for Materials Science
Wrought-processed Mg-Y-Zn alloys with long-period stacking ordered (LPSO) phase have exhibited high strength. The high strength is suggested to be related to the deformation kink bands formed by the wrought process. In the present study, hot compression tests were carried out on four types of cast Mg-Y-Zn alloys with the different volume fraction of the LPSO phase. After compression tests, deformation kink bands were observed in the LPSO phases, and the morphology differed depending on the compression temperature and the volume fraction of the LPSO phase. As the results of the hardness tests, the hardness shows a tendency with the increase of compressive strain or decrease of compression temperature. We discussed the microstructure including the morphology of the deformation kink band and the hardness.
Experimental Aspects of Kink and Pre-kink Formation Process in Mg-Zn-Y Alloy with LPSO Phase: Masatoshi Mitsuhara1; Tsubasa Tokuzumi1; Shigeto Yamasaki1; Hideharu Nakashima1; Koji Hagihara2; Toshiyuki Fujii3; 1Kyushu University; 2Osaka University; 3Tokyo Institute of Technology
The kink band formation process in Mg-6%Zn-9%Y alloy with the long-period stacking ordered (LPSO) phase was investigated in detail by in-situ compressive test and observation by SEM, and it succeeded in capturing the microstructural change with no surface relief which should be called as the pre-kink band. Using the SEM and the TEM analysis, it clearly founded that the pre-kink band involves the mobile and angle-variable terminated-subgrain-boundaries which consists of edge dislocation arrays. We are now developing the formation model of the pre-kink and kink band based on the disclination motion.
Deconvolution Analysis of AE Due to Kinking in Mg-Y-Zn Alloy: Takayuki Shiraiwa1; Naoya Hamada1; Fabien Briffod1; Manabu Enoki1; 1University of Tokyo
Compression tests of directionally-solidified (DS) Mg-Y-Zn alloys with long-period stacking ordered (LPSO) phase were conducted to observe the kinking behavior by a combination of a high-speed camera and acoustic emission (AE) method. The formation and propagation of kink bands were successfully captured at a sampling rate of 5M FPS. The kink bands were generated in a time of several microseconds. In-situ observations of twinning in pure Mg were also performed for comparison. The formation speed of the kink bands was almost constant regardless of its length in DS Mg-Y-Zn alloy, whereas the formation speed of the twin band is correlated with its band sizes in pure Mg. In order to evaluate the dynamic behavior of kinking quantitatively, deconvolution analysis was conducted for AE waveforms corresponding to kink band formation. Based on the results of deconvolution analysis, the statistics of the dynamic behavior of kinking will be discussed.
Effect of Deformation Path on Work-hardening Behavior in Long-period Stacking Ordered Phase of Mg-Zn-Y Alloys: Nozomu Adachi1; Yoshikazu Todaka1; Itsuki Fukuoka1; Hidetoshi Somekawa2; Daisuke Ando3; Motohiro Yuasa4; 1Toyohashi University of Technology; 2National Institute of Materials Science; 3Tohoku University; 4Doshisha University
Magnesium alloys with long-period stacking ordered phase are well known to have superior work hardening rate comparing with conventional magnesium alloys. Plastic deformation of long-period stacking ordered phase occurs though kink deformation with suppressing formation of twins. It is generally believed that kink-interfaces act as obstacles against slip deformation resulting in high work hardening rate. Therefore, it is important to control the fraction of kink-interfaces in the alloy during production process to achieve excellent mechanical properties. In this study, we have employed high-pressure torsion process which can switch a direction of shear strain during deformation, and the effect of deformation path on the formation of kink-interfaces has been investigated.
Fatigue and Fracture Behavior of Extruded Mg-Y-Zn Alloys Containing LPSO Phase: Fabien Briffod1; Wujun Yin1; Takayuki Shiraiwa1; Manabu Enoki1; 1University of Tokyo
The present study investigates the fatigue and fracture behavior of extruded Mg-Y-Zn alloys containing various amount of long-period stacking order (LPSO) phase. To this end, strain-controlled low-cycle fatigue, load-controlled high-cycle fatigue, and three-point bending tests are carried out. The results reveal a decrease in the fatigue life against the plastic strain amplitude with the increase in LPSO phase volume fraction but also an increase in the high-cycle fatigue limit. The latter one is associated with the decreasing presence of coarse equiaxed grains due to a higher recrystallization rate with the increase in LPSO content. Finally, bending tests reveals a shift in the fracture behavior from ductile to brittle with the increase in the LPSO phase volume fraction resulting in a decrease in fracture toughness. The present results are discussed in view of the different microstructural features of the α-Mg and LPSO phases.
In-situ Observation on the Formation Process of LPSO Structure in Mg Alloy by X-ray Absorption Spectroscopy: Kakeru Ninomiya1; Kooki Itamoto1; Kohei Fujino1; Maiko Nishibori1; 1Kyushu University
Long-period stacking (LPSO) type Mg alloy has the structure modulation and concentration modulation of the atomic arrangement in a long period. The LPSO structure has a hierarchical structure, which is composed of L12 clusters regularly arranged in-plane and out-of-plane. However, the formation mechanism of the LPSO structure has not yet been clarified.In this study, we have established the analysis method for the local structure of the L12 cluster by X-ray absorption spectroscopy and spectral simulation and considered the LPSO structure formation mechanism for Mg97Zn1Gd2 alloys. In-situ observations of the X-ray absorption fine structure spectra at the Zn-K and Gd-K absorption edges were performed under isothermal conditions of 673K. As a result, it was found that the spectral change with the heat treatment time was successfully observed and that the 14H-LPSO structure of the Mg97Zn1Gd2 alloy was formed in several steps.