Magnesium Technology 2017: Mechanical Behavior: Twinning, Plasticity, Texture, and Fatigue III
Sponsored by: TMS Light Metals Division, TMS: Magnesium Committee
Program Organizers: Kiran Solanki, Arizona State University; Dmytro Orlov, Lund University; Alok Singh, National Institute for Materials Science; Neale Neelameggham, Ind LLC

Thursday 2:00 PM
March 2, 2017
Room: 5B
Location: San Diego Convention Ctr

Session Chair: Christopher Barrett, Mississippi State University; Vineet Joshi, Pacific Northwest National Laboratory

2:00 PM  
Microstructure and Texture Evolution during Hot Deformation of Cast-Homogenized ZK60 Magnesium Alloy: Amir Hadadzadeh1; Sugrib Shaha1; Mary Wells1; Hamid Jahed1; Bruce Williams2; 1University of Waterloo; 2CanmetMATERIALS, Natural Resources Canada
    Forgeability of cast ZK60 magnesium alloy was investigated by isothermal uniaxial hot compression of cylindrical samples using the Gleeble 3500 thermal-mechanical simulation testing system. Computational thermodynamics predictions (by FactSage™) along with differential scanning calorimetry (DSC) experiments showed incipient melting of low melting temperature precipitates in the as-cast material at around 340C. Therefore, the as-cast material was subjected to homogenization heat treatment at 400C for 4 hours. Hot compression test were then conducted at 400 and 450C using a variety of strain rates (0.001-1.0s-1). The microstructure of the samples deformed at low strain rates consisted of dynamically recrystallized (DRXed) grains. By increasing the strain rate, the volume fraction of the DRXed regions reduced. The material also exhibited sensitivity to deformation temperature in terms of DRX volume fraction. Texture of the deformed samples was also characterized using the XRD method to investigate the effect of hot deformation conditions on the texture evolution.

2:20 PM  
Microstructure Evolution during Tensile Tests and Its Correlation with Ductility of Mg Sheets: Zhuoran Zeng1; Mingzhe Bian1; Shiwei Xu2; Chris Davies1; Nick Birbilis2; Jian-Feng Nie1; 1Monash University; 2Baosteel Group Corporation
    Hot-rolled sheets of dilute Mg-Zn-Ca alloys are promising for automotive applications because of their low cost and better ductility than AZ31 sheets. However, the origin of their better ductility is controversial, primarily due to the lack of direct observations of microstructure evolution in these sheets during tensile tests. In the present study, the Mg-0.3Zn-0.1Ca, Mg-0.4Zn and Mg-0.1Ca (all in at. %) sheets are hot-rolled at 450C and annealed at 400C. Their ductility is measured by tensile tests at room temperature. It is found that the ductility of the ternary alloy sheet is much better than those of binary alloys. To understand the difference in ductility of these alloy sheets, their microstructures, such as traces of dislocation slips, twinning, cracking, and texture at different stages of tensile testing are systematically monitored using a quasi-in-situ EBSD method, and results are compared. The correlations between microstructural evolution and alloy ductility will be discussed.

2:40 PM  
Effect of Ca on the Microstructure, Texture and Mechanical Properties in Mg-Zn-Mn Based Alloy: Byeong-Chan Suh1; Taisuke Sasaki1; Taiki Nakata2; Shigeharu Kamado2; Kazuhiro Hono1; 1National Institute for Materials Science; 2Nagaoka University of Technology
    In order to broaden the applications of magnesium alloys, there is a strong demand for the development of Mg alloy sheets deformable at room temperature. We investigated the effect of Ca addition on the microstructures and mechanical properties of Mg-4Zn-0.4Zr (ZK40) (wt.%) hot-rolled sheets. The solution treated ZK40 and ZKX400 alloys exhibit bimodal grain structures. While coarse unrecrystallized grains remain in the ZK40, fully recrystallized grain structure is formed in the ZKX400. The addition of Ca results in texture weakening with substantial decrease in the maximum (0001) pole intensity from 13.4 to 4.8. This leads to a substantial improvement of index Erichsen value from 3.5 to 7.5 mm. The tensile yield strength of ZKX400 is 176 MPa, which is higher than that of ZK40, 160 MPa. Since Mg-Zn based alloys are precipitation hardening system, further compositional optimization is expected to increase the strength of the deformed sheet by artificial aging.

3:00 PM  
Evaluation of In Vitro Fatigue Properties of Biodegradable Mg-0.3at.%Ca Alloy: Naoko Ikeo1; Akihito Taguma1; Taichi Uemura1; Toshiji Mukai1; 1Kobe University
    Recently, biodegradable bone fixation devices have been demanded when considering the patient's QOL. During the fracture healing, the devices must support the repeated load due to daily performance. At the same time, surface of the magnesium devices was affected by body fluid. Thus in this research, in vitro fatigue properties of biodegradable Mg-0.3 at.% Ca alloy was evaluated by using simulated body fluid. Though there was fatigue limit when the test was conducted under the ambient condition, it cannot be confirmed during the test in the simulated body fluid. Inspection of fracture surface revealed that crack propagated along the grain boundary after both the fatigue tests.

3:20 PM  
Mechanical Properties and Fatigue Strength of Extruded Cobalt-containing Magnetic Magnesium Alloys: Christian Demminger1; Christian Klose1; 1Leibniz Universitaet Hannover
    Magnetic magnesium alloys have inherent magnetic properties due to cobalt, which is used as an alloying element here. The magnetic properties mainly originate from Co-rich precipitates and the mechanical properties are significantly influenced by the alloys’ microstructures. Previous works showed comparatively weak mechanical strength of magnetic magnesium specimens produced by gravity die-casting due to the precipitation structure. In this work, the influence of extrusion on the mechanical properties and the microstructure of magnetic magnesium alloys is investigated. Extrusion billets were manufactured from a Mg-Co-Zn alloy by means of a gravity die-casting method. The billets were then extruded to circular bars and a water-air spray cooling was used to affect recrystallization processes during extrusion. Afterwards, the mechanical properties were examined by tensile and rotation-bending tests and correlated with micrographs. For technical applications, the fatigue strength is of major importance, hence the results are discussed and compared with literature.

3:40 PM Break

4:00 PM  
Neutron Diffraction and Acoustic Emission Measurement during Loading and Unloading of Magnesium Aluminium Binary Alloys: Jan Čapek1; Kristian Mathis1; 1Charles University in Prague
    The neutron diffraction and acoustic emission were measured during compression loading-unloading tests in randomly textured cast magnesium and magnesium 2 wt.% and 9 wt.% aluminium binary alloys. The anelastic behavior and the change of twinned volume related to the detwinning phenomena can be observed during the unloading. The decrease of twinned volume fraction during unloading is most pronounced for Mg 9 wt.% Al.

4:20 PM  
Texture Weakening and Grain Refinement by High Speed Rolling and Annealing of an AZ31 Magnesium Alloy: Jing Su1; Stephen Yue1; 1McGill University
    It is well known that formation of the strong basal textures in Mg alloy sheets is detrimental to the formability of the sheets during further forming process. Texture randomization by adding rare earth (RE) elements (e.g. Gd, Ce) in Mg alloy has shown potential to improve the ductility and formability. This is related to the unique basal textures with double poles splitting along both the rolling direction (RD) and transverse direction (TD) of the Mg-RE alloys sheets, instead of the single peak basal texture formed in conventional Mg alloys. In the present study, by applying normal-rolling and cross-rolling with intermediate annealing at 200C, RE-texture components were produced in an AZ31 alloy with a relatively low intensity of the texture. In addition, the final microstructure was uniform and fine with the average grain size of 4 m.

4:40 PM  
The Relative Contributions of Deformation Modes to AZ31 Rolling Textures in Different Temperature Regimes: Matthew Steiner1; Jishnu Bhattacharyya1; Sean Agnew1; 1University of Virginia
    The {0001}〈11 ̅20〉 texture in warm-rolled Mg alloy AZ31B, recently discovered to strongly evolve during grain growth annealing, is the result of a grain size advantage that emerges during recrystallization; where grains closer to the {0001}〈11 ̅20〉 orientation are larger on average than competing {0001}〈10 ̅10〉 oriented grains. Starting from EBSD data of recrystallized microstructures, Potts Monte Carlo methods are used to model textural evolution due to grain growth that arises from this orientation-size interdependence in the recrystallized microstructure. To highlight the significant role that recrystallization conditions play in the subsequent grain growth microstructure, five AZ31B samples were recrystallized at conditions between 250C and 450C and exposed to an identical week long heat treatment at 400C, with their microstructures analyzed by EBSD before and after heat treatment. The first several minutes of recrystallization are shown to have a large effect on the resulting textural evolution during subsequent grain growth.

5:00 PM  
Effects of Texture and Triaxiality on the Plasticity of Magnesium Alloys: Balaji Selvarajou1; Shailendra Joshi1; Amine Benzerga2; 1National University of Singapore; 2Texas A & M University
    Understanding the role of triaxiality is key in the damage evolution of engineering alloys. In low symmetry materials, e.g. magnesium, the role of triaxiality in damage evolution is complicated by the presence of protean deformation mechanisms, which exhibit high crystallographic plastic anisotropy. We present the results of detailed finite element study of smooth and notched round bar polycrystalline specimens of magnesium, subjected to quasi-static tensile loading. Initial simulated textures mimicking and deviating from typical rolled Mg sheet textures are adopted. Using three-dimensional HCP single crystal plasticity, the effect of these textural variations is highlighted. The role of out-of-plane textural variation is compared to the in-plane variation, and the analysis indicates that out-of-plane deviations in result in subtle changes to the macroscopic deformation anisotropy and the underlying microscopic deformation slip and twin activity. The role of these textures in the activation of twinning mechanisms is discussed. These results, in conjunction with our recent works, help develop a systematic understanding of the texture-triaxiality-anisotropy interaction in magnesium alloys.