12th International Conference on Magnesium Alloys and their Applications (Mg 2021): Deformation & Mechanical Behaviors II
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
Thursday 10:50 AM
June 17, 2021
Room: Contributed IV
Location: Virtual
Session Chair: Matthew Barnett, Deakin University
The Role of Intermetallic Particle Morphology and Position in Twin Transmission across Grain Boundaries: Benjamin Anthony1; Victoria Miller1; 1University of Florida
Deformation twins in magnesium alloys contribute to early failure during room temperature forming by providing void nucleation sites and preferential crack pathways. This is particularly true for instances of twin transmission where the stress imposed at a grain boundary by a twin nucleates a new twin in the neighboring grain, leading to thicker twins and longer continuous twin boundaries. Many commercial alloys feature coarse intermetallic particles at the grain boundaries in their as-solidified state, but the role of these particles in modifying twinning behavior has only been studied computationally. Experimental validation via electron backscatter diffraction is used to perform a statistical analysis of twinning in thixomolded AM60 with varying particle volume fractions to determine their effect on twinning behavior and transmission frequency, particularly with respect to size, aspect ratio, and distance from the impingement site.
The Role of Dislocation Climb in the High Temperature Deformation of Mg alloys AZ31B and ZK10 and the Distinctions in the Activity of Dislocations with a c-type Burgers Vector: Michael Ritzo1; Sean Agnew1; 1University of Virginia
Tensile samples of a Mg alloys AZ31B and ZK10 sheet were tested at a range of temperatures and strain rates designed to rather evenly probe a similar range of Zener-Hollomon (Z) parameter values. A version of the viscoplastic self-consistent (VPSC) code, which accounts for the kinematics of dislocation climb, is used to model the behavior. Both alloys exhibit a transition in the r-values and texture evolution at some value of Z. Below this critical value the constitutive response transitions to a power law and the modeling reveals that dislocation climb plays a significant role in strain accommodation. While the behavior of AZ31B does not demand activity of dislocations with a c-type Burgers vector, the ZK10 alloy does. TEM-based investigation of dislocations in samples deformed above and below the aforementioned transition is employed to provide an explanation for the distinct behavior of the two alloys.
Continuous ECAP Processing of Mg Alloys: Adam Griebel1; Casey Davis2; Jeremy Schaffer1; Terry Lowe2; 1Fort Wayne Metals; 2Colorado School of Mines
Nutrient metal implants designed to absorb into the body over time promise a future with fewer follow up surgical procedures and long-term complications. Alloys based on magnesium hold the most promise for widespread implementation in these applications. Absorbable magnesium devices generally benefit from materials with increased strength, ductility, and localized corrosion resistance. High shear deformation techniques like ECAP can improve properties in each of these three categories. Continuous ECAP processing offers ultrafine grain benefits of traditional ECAP, but on a production-level scale. This presentation will review the implementation to-date of continuous ECAP processing on Mg alloys.
An Investigation of the Mechanism of the Negative Strain Rate Sensitivity of Mg Alloys: Mohammed Shabana1; Laurent Capolungo2; Sean Agnew1; 1University of Virginia; 2Los Alamos National Laboratory
Many solute strengthened alloys exhibit dynamic strain aging (negative strain rate sensitivity and often serrated flow) at particular strain rates and temperatures, and Mg alloys are no exception. It has for some time been suggested that interactions between mobile and forest dislocations are required to explain these phenomena. In a seminal work published in 2004, Picu outlined a specific mechanism for the negative strain rate sensitivity of dilute solid solutions and performed a parametric investigation of the Lomer lock case relevant to FCC alloys. In the case of HCP Mg alloys, the interactions between basal and prismatic dislocations do not have any such locked configurations. Rather, annihilation and glissile junction formation are the relevant cases. A parametric study is performed in which mobile basal dislocations encounter prismatic forest dislocations and vice versa. Implications for dynamic strain aging in Mg alloys are discussed.
Effect of Gd and Nd Additions on the Mechanical Behaviors of Extruded Mg Alloys: Yuling Xu1; Shiwei Wang2; Yuye Wang2; Lü Xiao2; Norbert Hort3; 1Chongqing Academy of Science and Technology; 2Shanghai Spaceflight Precision Machinery Institute; 3 MagIC-Magnesium Innovation Center, Helmholtz-Zentrum Geesthacht
The influence of alloy elements and heat treatment on the microstructure and mechanical behaviors of four extruded Mg–Gd–Nd ternary alloys are discussed in this study. The grain sizes of extruded alloys decrease from 26 to 5 μm with alloy content increasing after extrusion. The mechanical test results show that both Gd and Nd have positive effect on the hardness, yield strength and Young’s modulus. The ultimate tensile strength (UTS) is enhanced by Gd, but decreased with Nd content. The elongation of alloys is lower with higher alloy elements. Those extruded alloys were aged for 200 h in 200℃. The Young’s moduli are decreased by ageing treatment. Combined with microstructure study, part of reinforcement which identified as Mg5(Gd,Nd) phase is solved in Mg matrix. On the other hand, the β’ precipitates were distributed in grains which leads the great improvements of yield strength.
Effect of Adding Third Element on Deformability of Mg-Al Alloy: Kazuki Senoo1; Tatsuya Nakatsuji1; Naoko Ikeo1; Masatake Yamaguchi2; Toshiji Mukai1; 1Kobe University; 2Japan Atomic Energy Agency
In recent years, magnesium is expected to be used as a structural material in vehicles. Since limited slip systems in magnesium induces marked yield anisotropy and poor deformability at room temperature, there is a certain demand for developing magnesium alloys having improved plastic anisotropy. In this study, we focused on the Mg-Al system alloy, which is widely used in commerce, and examined a third element that contributes to improve the plastic anisotropy. Generalized stacking fault energy (GSFE), which corresponds to the energy for sliding atomic layer along a slip plane, was calculated in the first-principles calculations to estimate deformability of ternary Mg-Al-X alloys adding the third element, X, to the Mg-Al binary alloy. As a result, it was suggested that the addition of zirconium contributes most to the reduction of plastic anisotropy. Mechanical characterization revealed the effect of the third element on the deformability at room temperature.