Heterogeneity in deformation and twinning behaviors through the thickness direction in E-form Mg alloy sheets during an Erichsen test

Singh, Jaiveer,Kim, Min-Seong,Lee, Seong-Eum,Kim, Eun-Young,Kang, Joo-Hee,Park, Jun-Ho,Kim, Jae-Joong,Choi, Shi-Hoon Elsevier 2018 Materials science & engineering. properties, micro Vol.729 No.-

<P><B>Abstract</B></P> <P>The heterogeneity of both deformation and twinning behaviors through the thickness direction in E-form Mg alloy sheets was investigated via conventional Erichsen testing at room temperature (RT). The microtexture heterogeneity through the thickness direction of the E-form Mg alloy sheets deformed by different punch strokes (PSs) is discussed in terms of deformation twinning and de-twinning. The evolution of the microtexture, twin and KAM (kernel average misorientation) of E-form Mg alloy sheets deformed by different PSs was analyzed via electron back-scattered diffraction (EBSD) technique. A crystal plasticity finite element method (CPFEM) based on a random mapping (RM) scheme was used to simulate the heterogeneities of the strain/stress states of E-form Mg alloy sheets through the thickness direction during an Erichsen test. The evolution of the strain/stress that developed in E-form Mg alloy sheets during Erichsen testing was analyzed for different regions through the thickness direction under different PSs. EBSD analysis revealed that tension (TTWs), compression (CTWs) and double (DTWs) twins were the main deformation mechanisms in the upper portions. However, in the lower portions, a change in the sign of strain/stress components during Erichsen testing resulted in a significant formation of TTWs in the early stages and in a de-twinning of TTWs in the later stages.</P>

Microstructure evolution and deformation behaviors of E-form and AZ31 Mg alloys during <i>ex-situ</i> mini-V-bending tests

Singh, Jaiveer,Kim, Min-Seong,Lee, Ji-Hyun,Guim, Hwanuk,Choi, Shi-Hoon Elsevier 2019 Journal of Alloys and Compounds Vol.778 No.-

<P><B>Abstract</B></P> <P>Microstructure evolution in E-form and AZ31 magnesium (Mg) alloys was studied via <I>ex-situ</I> mini-V-bending tests. Initially, the E-form and AZ31 Mg alloys had different crystallographic textures and average grain-size distributions. Direct observation of microstructural evolution during the <I>ex-situ</I> mini-V-bending tests was experimentally observed via electron back-scatter diffraction (EBSD) technique. The EBSD results revealed how twin bands (TBs) developed at different punch strokes (PSs) in the deformed grains made a significant contribution to the localized deformation zones in both Mg alloys under the mini-V-bending process. Eventually, the TBs and grain boundaries (GBs) in the localized deformation zones were responsible for crack initiation sites in the tension region. At lower PSs, compression (CTW) and double (DTW) twins were more prominent in E-form than in AZ31 under the mini-V-bending process. High-resolution cross-sectional t-EBSD analysis showed that surface relief allowed the grains residing on the free surface to be less affected by stress concentration while the sub-surface grains were more affected by stress concentration, which promoted the development of twinning.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Microstructure evolution were studied via <I>ex-situ</I> mini-V-bending tests. </LI> <LI> Direct observation during the <I>ex-situ</I> mini-V-bending tests was conducted via EBSD technique. </LI> <LI> TBs and GBs in the localized deformation zones were responsible for crack initiation sites in the tension region. </LI> <LI> CTW and DTW were more prominent in E-form Mg alloy than AZ31 Mg alloy under the mini-V-bending process. </LI> <LI> High-resolution t-EBSD was conducted to reveal the deformation behavior of the grains residing on the free surface. </LI> </UL> </P>

The effect of strain heterogeneity on the deformation and failure behaviors of E-form Mg alloy sheets during a mini-V-bending test

Singh, Jaiveer,Kim, Min-Seong,Choi, Shi-Hoon ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.708 No.-

<P><B>Abstract</B></P> <P>Deformation and failure behaviors of E-form magnesium (Mg) alloy sheets were investigated using a mini-V-bending test. The evolution of the microstructure and microtexture of the deformed E-form Mg alloy sheets (before and after failure) was analyzed via an electron back-scattered diffraction (EBSD) technique. Finite element analysis (FEA) was used to capture the heterogeneous distribution of longitudinal-strain components through the thickness direction under mini-V-bending at different punch strokes. The relationships between punch stroke, bending radius and longitudinal-strain at the tension and compression zones were established. EBSD analysis revealed that shear localization by dislocation slip along with compression and double twins were the main deformation mechanisms in the tension zone while tensile twins were a main deformation mechanism in the compression zone in E-form Mg alloy sheets during mini-V-bending. The effect that deformation twinning had on the crack propagation sites in E-form Mg alloy sheets was also investigated. The networks of compression { 10 1 ¯ 1 } and double { 10 1 ¯ 1 } − { 10 1 ¯ 2 } twins in the tension zone of E-form Mg alloy sheets were closely related to the crack propagation during mini-V-bending at near room temperature (RT).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Strain heterogeneity in bended E-form Mg sheets induces microtexture heterogeneities. </LI> <LI> The networks of compression and double twins are related to crack propagation during mini-V-bending. </LI> <LI> FEA captured the heterogeneous distribution of the longitudinal strain component in a bended specimen during mini-V-bending. </LI> <LI> Intragranular cracking was a dominant mechanism for failure in the tension zone during mini-V-bending. </LI> <LI> Localized deformation zones were mostly confined to the twin and grain boundaries. </LI> </UL> </P>

Mesoscale Simulation of Deformation Behaviors of E‑form and AZ31 Mg Alloys During Ex‑Situ Mini‑V‑Bending Tests

Jaiveer Singh,Min‑Seong Kim,Joo‑Hee Kang,Shi‑Hoon Choi 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3

Mesoscale simulations based on the resolved shear stress (RSS) analysis and the crystal plasticity finite element method(CPFEM) simulations were used to elucidate the deformation behaviors of E-form and AZ31 magnesium (Mg) alloys andthe evolution of tension twin (TTW) and compression twin (CTW) variants during mini-V-bending. RSS analysis, which isbased on the Schmid tensor, was used to calculate the type of twin variants and the number of TTW and CTW variants thatevolved in the deformed Mg alloys. However, RSS analysis considers neither the critical resolved shear stress (CRSS) oftwin systems nor the interaction with neighboring grains, and it failed to accurately predict the twin behaviors of deformedgrains. This study simulated the spatial distributions of the relative activities of different deformation modes, accumulatedtwin fractions, accumulated plastic strains, and effective stresses via CPFEM. Compared with the RSS analysis, CPFEMsimulation precisely explained the twin behaviors observed in both E-form and AZ31 Mg alloys.

The effect of initial texture on micromechanical deformation behaviors in Mg alloys under a mini-V-bending test

Singh, Jaiveer,Kim, Min-Seong,Choi, Shi-Hoon Elsevier 2019 International journal of plasticity Vol.117 No.-

<P><B>Abstract</B></P> <P>Micromechanical deformation behaviors of E-form fine grain (EFG), E-form coarse grain (ECG), and AZ31 magnesium (Mg) alloys were investigated and compared using a mini-V-bending test. EFG and ECG Mg alloys with a weaker texture showed better bendability compared with AZ31 alloy that has a stronger texture. The evolution of the microstructure and microtexture during the mini-V-bending process was experimentally analyzed via an electron back-scattered diffraction (EBSD) technique. This study was focused on the effect that deformation twinning exerts on the strain localization and crack initiation. The twin bands (TBs) developed in the tension zone of bent specimens found to be closely related to the strain localization and crack initiation during the mini-V-bending process. A resolved shear stress (RSS) criterion and microstructure based crystal plasticity finite element method (CPFEM) were used to theoretically predict the activation of { 10 1 ¯ 2 } tension (TTW) and { 10 1 ¯ 1 } compression (CTW) twins in Mg alloys under a mini-V-bending process. RSS analysis indicated that EFG and ECG Mg alloys are more favorable for the activity of TTW and less favorable for the activity of CTW when compared with AZ31 Mg alloy during a mini-V-bending process. However, RSS analysis was not effective in quantitatively predicting twin development. The relative activities of six deformation modes, accumulated twin fractions, and accumulated plastic strains were simulated via microstructure-based CPFEM modeling. Compared with RSS analysis, CPFEM precisely explained the twin behavior that has been experimentally observed in ECG and AZ31 Mg alloys.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effects of initial texture and grain size in Mg alloys under mini-V-bending tests were investigated. </LI> <LI> The micromechanical deformation behavior was studied using EBSD analysis, RSS criterion, and mesoscale CPFEM modeling. </LI> <LI> Deformation twinning was more prominent in ECG and EFG Mg alloys than in AZ31 Mg alloy during the mini-V-bending. </LI> <LI> In contrast to the RSS criterion, CPFEM modeling more accurately described the twin behavior observed in the experiments. </LI> <LI> The primary deformation mode in ECG and AZ31 Mg alloys was basal '> a and pyramidal '> c + a slip, respectively. </LI> </UL> </P>

Mini V-bending 시험 시 Mg합금 판재의 굽힙성에 관한 연구

김민성,Jaiveer Singh,최시훈 한국소성가공학회 2017 한국소성가공학회 학술대회 논문집 Vol.2017 No.5

Mini V-bending 시험 시 Mg합금의 굽힙성에 미치는 이방성의 영향

김민성,Jaiveer Singh,이성음,박준호,김재중,최시훈 한국소성가공학회 2018 한국소성가공학회 학술대회 논문집 Vol.2018 No.5

Effect of microstructure on the hardness heterogeneity of dissimilar metal joints between 316L stainless steel and SS400 steel

Jahanzeb, Nabeel,Shin, Ji-Hwan,Singh, Jaiveer,Heo, Yoon-Uk,Choi, Shi-Hoon Elsevier Sequoia 2017 Materials science & engineering Structural materia Vol.700 No.-

<P><B>Abstract</B></P> <P>The dissimilar weld joints between 316L austenitic stainless steel and SS400 ferritic steel were used to investigate the effect that microstructure exerts on hardness heterogeneity in weld joints. In order to identify the constituent phases and deformation mechanisms in the dissimilar weld joints, microstructure characterization of undeformed and deformed specimens was conducted via optical microscope (OM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM) techniques. Micro-hardness measurements across the different weld regions and mini-tension testing combined with digital image correlation (DIC) were conducted to evaluate the mechanical properties of the base metals (BMs), the weld zone (WZ), and the heat-affected zone (HAZ). Local strain heterogeneity on deformed specimens was also explained by microstructure heterogeneity in terms of grain morphology and constituent phases. Non-uniform enhancements of the strain distributions were distinct in the WZ, which consisted of a dendritic structure with a irregular morphologies. Uneven patterns of a martensite transformation from γ to α′ in the 316L contributed to localized heterogeneity in the strain distribution.</P>

Texture Control Techniques for Improving Room Temperature Formability of Mg Alloys including Pre-twinning: A Review

Mahesh Panchal,K. R. Ravi,Lalit Kaushik,Rajesh Khatirkar,Shi‑Hoon Choi,Jaiveer Singh 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.12

Magnesium (Mg) alloys are the lightest among the structural metallic materials and have attracted great interest due to theirhigh specific strength and specific stiffness. However, Mg alloys show poor formability particularly at room temperature(RT), due to the development of strong basal texture and thus limiting their structural applications. Therefore, many techniquesbeing constantly proposed to alter the crystallographic texture in Mg alloys, such as microalloying, especially withrare-earth (RE) elements, severe plastic deformation (SPD), thermomechanical processing (TMP), pre-twinning/stretchingin the recent past. Pre-twinning remains the most effective technique that controls the crystallographic texture in Mg alloysby introducing 1012 extension twins (ETs) which work out for alloys prepared through various prior processing conditionsand compositions. Interestingly, only a small fraction of ETs during pre-twinning imparts significant improvement in the RTstretch formability. Therefore, this manuscript critically reviews the underlying mechanisms of pre-twinning and texturecontrol via practical pre-twinning methods such as in-plane compression and compares its effectiveness with other texturecontrol methods through alloy design, TMP, and SPD processes. In addition, the effect of initial microstructure and variousdeformation conditions on the contribution of twin, twin-orientation control during thermal treatment and also their influenceon the RT stretch formability are discussed.