Magnesium Technology 2020: Alloy Design and Solidification
Sponsored by: TMS Light Metals Division, TMS: Magnesium Committee
Program Organizers: J. Brian Jordon, Baylor University; Victoria Miller, University of Florida; Vineet Joshi, Pacific Northwest National Laboratory; Neale Neelameggham, IND LLC
Tuesday 8:30 AM
February 25, 2020
Room: 6C
Location: San Diego Convention Ctr
Session Chair: Matthew Kasemer, The University of Alabama
8:30 AM Invited
Insights on Solidification of Mg and Mg-Al Alloys by Large Scale Atomistic Simulations: Mohsen Asle Zaeem1; Avik Mahata2; Sepideh Kavousi1; 1Colorado School of Mines; 2Missouri University of Science and Technology
Solid-liquid interface properties and rapid directional solidification of Mg and Mg-Al alloys are studied by large scale molecular dynamics (MD) simulations. Second nearest neighbor modified embedded atom method (2NN-MEAM) interatomic potentials are utilized to describe the atomic interactions at high temperatures. The anisotropy of the hexagonal close-packed (HCP)-liquid interface free energy is studied utilizing the capillary fluctuation method, and the solid–liquid coexisting approach is used to accurately determine the melting point and melting properties. The first preferred dendrite growth direction in solidification of Mg is predicted as [112-0], which is in agreement with experiments. At the initial stages of rapid directional solidification, several solidification defects such as twins and stacking faults form. As directional solidification progresses, grains elongate along the solidification direction and form a few layers with lamellar like structures. The directional solidification in Mg-Al alloys consists of considerable amount of heterogeneities including formation of Mg17Al12 precipitates.
9:00 AM
CALPHAD Modeling and Microstructure Investigation of Mg-Gd-Y-Zn Alloys: Janet Meier1; Joshua Caris2; Alan Luo1; 1The Ohio State University; 2Terves LLC
In this study, the predictive capabilities of CALPHAD (CALculation of PHAse Diagrams) modeling were used to design and optimize Mg-Gd-Y-Zn alloys containing long period stacking order (LPSO) phases. The selected compositions were evaluated using scanning electron microscopy, electron dispersive spectroscopy, and x-ray diffraction to determine the volume fractions of major phases. It was seen that LPSO 14H formed at the grain boundaries and a filament-type LPSO 14H formed in the Mg grains. As the RE and Zn concentration increased, eutectic Zn rich intermetallics and RE rich phases formed along grain boundaries. With annealing an increase in hardness was observed due to the increase in intermetallic volume fraction, decrease in bulky LPSO volume fraction, and increase in filament-type LPSO. These results indicate the present CALPHAD databases well represent the Mg-Gd-Y-Zn system studied and can be used to tailor the microstructure to potentially improve the strength and ductility in these alloys.
9:20 AM
Intermetallic Phase Formation in Mg-Ag-Nd (QE) and Mg-Ag-Nd-Zn (QEZ) Alloys: Rainer Schmid-Fetzer1; Jian-Feng Nie2; Xiaojun Zhao3; Houwen Chen3; 1Clausthal University of Technology; 2Monash University; 3Chongqing University
The intermetallic phase in the solution-treated microstructure of commercial magnesium alloy QE22 (Mg-2.5Ag-2.0Nd-0.7Zr, wt.%) has been investigated using scanning electron microscopy, electron diffraction, atomic-resolution scanning transmission electron microscopy (STEM) and thermodynamic modeling. In contrast to previous reports the orthorhombic structure (space group Cmcm, a = 1.02 nm, b = 1.18 nm, c = 1.00 nm) and a composition of NdAgMg11 are determined. The present experimental data are used to construct a thermodynamic description of the Mg-Ag-Nd system which is embedded in a multicomponent Mg alloy database. Implications on the formation temperature range and thermal stability of this phase and alloy solidification are discussed based on the calculated Mg–Nd–Ag phase diagram and Scheil solidification paths of alloys. The impact of Ag-replacement in such QE alloys by Zn-addition in the Mg-Ag-Nd-Zn (QEZ) alloy system is elaborated using appropriate thermodynamic simulations to reveal the competition with other intermetallics.
9:40 AM
Recrystallization Effects on the Forming Behaviour of Magnesium Alloy Sheets with Varied Calcium Concentration: Jan Bohlen1; Huu Chanh Trinh2; Klaus Rätzke2; Sangbong Yi1; Dietmar Letzig1; 1Magic-Magnesium Innovation Ctr; 2Christian-Albrechts-University
The formation of strong textures with a preferential alignment of the basal planes in the sheet plane were an important disadvantage for the formability of magnesium alloy sheets. Rare earth or calcium alloying concepts allow significant texture changes during rolling, resulting in weaker textures and thus improved formability. Such a texture development has also been associated with retarded recrystallization. However, this retardation affects the formability during sheet forming operations at elevated temperature.The wrought alloy AZ31 and its Ca-modified counterpart AZX310 are used for Nakajima forming tests at different temperatures and deformation rates. The influence of recrystallization on the sheet formability is demonstrated along different strain paths including local microstructure analysis. The weaker texture due to the addition of Ca allows maintaining the improved formability, which is counteracted by retarded recrystallization. A balance of both effects is discussed.
10:00 AM
Towards the Development of High Ductility Mg-Al Based Alloys Through Second-phase Refinement with Trace Yttrium Additions: Konstantinos Korgiopoulos1; Mihriban Pekguleryuz1; 1Mining and Materials Engineering, McGill University
Magnesium alloys are attractive lightweight materials for transport industry as they offer a viable approach for reduced CO2 emissions and fuel economy. The most widely used alloys for automotive applications are based on the Mg-Al system where the principal second phase β-Mg17Al12 provides strengthening but reduces ductility. A key factor in widening the use of magnesium in crashworthy components such as vehicle body applications is the availability of cost-effective Mg casting alloys with improved ductility. Modification of the Mg17Al12 in Mg-Al alloys via trace additions is a promising approach to enhance the ductility while maintaining the strength. Our research has found that only trace levels of yttrium (Y) can modify the Mg17Al12 and improve the ductility of Mg-6Al alloy by 63%. To elucidate the mechanism of this refinement, different methods are used including thermodynamic calculations, image analysis, scanning and transmission electron microscopy.
10:20 AM Break
10:40 AM
Effects of Zn Additions on the Room Temperature Formability and Strength in Mg-1.2Al-0.5Ca-0.4Mn Alloy Sheets: Zehao Li1; Taisuke Sasaki1; Kazuhiro Hono1; Mingzhe Bian1; Taiki Nakata; Shigeharu Kamado1; Yu Yoshida1; Nozomu Kawabe1; 1NIMS
Recent studies have suggested that the Mg-Al-Zn-Mn-Ca system is promising to conquer the strength-formability trade-off dilemma. In this work, the role of Zn in the microstructure and mechanical properties in the Mg-1.2Al-0.5Ca-0.4Mn-xZn (wt.%, x=0, 0.8 and 1.6) alloy sheets is clarified based on the detailed microstructure characterization. The room-temperature stretch formability of the solution-treated sheet is improved with increasing the Zn content. The Mg-1.2Al-0.5Ca-0.4Mn-1.6Zn alloy shows an excellent stretch formability with the largest Index Erichsen (I.E.) value of 8.2 mm due to a weak transverse direction split texture. Subsequent artificial aging at 170 °C for 2h (T6) leads to substantial increase in strength without the loss of ductility. The peak-aged Mg-1.2Al-0.5Ca-0.4Mn-1.6Zn alloy exhibits a high tensile yield stress of 210 MPa with a good elongation of 30.1% because of a dense dispersion of Guinier-Preston (G.P.) zones within the Mg matrix.
11:00 AM
Application of Three-phase Miscibility Gap Formation Mechanisms in Mg Alloys: Shuanglin Chen1; John Morral2; 1CompuTherm LLC; 2The Ohio State University
Spinodal decomposition is one of the strengthening mechanisms in Mg alloys. Binary two-phase miscibility gaps and spinodal lines are well known and can be found in textbooks. Three-phase miscibility gaps can also form in ternary and higher order systems from a thermodynamic standpoint. Mechanisms to form three-phase miscibility gaps will be summarized based on the work by Gibbs, Schreinemakers and Meijering. Three-phase miscibility gaps, spinodal lines and critical points will be calculated to illustrate how they change with temperature and compositions. Examples in Mg alloys will be presented to demonstrate how the calculated miscibility gaps and spinodal lines can help us better understand phase stabilities and spinodal decomposition during heat treatment process of the alloys.
11:20 AM Cancelled
Investigation of the Microstructure and Mechanical Properties of Mg–Gd–Nd Ternary Alloys: Yuling Xu1; Lixiang Yang2; Weili Liu3; Jingli Sun; Lu Xiao3; Xianquan Jiang1; Norbert Hort4; 1Chongqing Academy of Science and Technology; 2Shanghai Jiaotong University; 3Shanghai Spaceflight Precision Machinery Institute; 4Helmholtz Zeetrum Geesthacht
The present work deals with microstructure and mechanical properties of Mg–xGd–yNd (x = 10, 15; y = 2, 5) ternary Alloys. Hardness, tensile and compressive properties are measured on the as-cast alloys and the alloys after solid solution treatment (T4 state). The hardness, tensile yield stress (TYS) and ultimate tensile stress (UTS) are increased with increasing of alloy elements for both as-cast and T4 state alloys. The elongations (El) of alloys are lower with higher Nd content. The compressive properties of all studied alloys are increased by T4 treatment. With increasing of alloy concentration, both compressive yield stress (CYS) and ultimate compressive stress (UCS) of alloys are enhanced, but the compressibility is decreased. Intermetallic compounds which appear along the grain boundary are reduced after T4 treatment for alloys with 2% Nd. However, large amount of intermetallic with high Nd concentrations remains on the grain boundary of Mg–xGd–5Nd alloys.
11:40 AM Cancelled
Design of Heat Dissipating Mg–La–Zn Alloys based on Thermodynamic Calculations: Hui Shi1; Qun Luo1; Qian Li1; Jieyu Zhang1; Kuo-Chih Chou2; 1State Key Laboratory of Advanced Special Steel & Shanghai Key Laboratory of Advanced Ferrometallurgy & School of Materials Science and Engineering, Shanghai University & Shanghai Institute of Materials Genome & Materials Genome Institute; 2Shanghai University
In this study, nine heat dissipating alloys were designed by thermodynamic phase diagram calculations in Mg–La–Zn system. The temperature dependence of thermal conductivities of as-cast Mg–xLa–yZn (x=0.17–0.57at.%, y=0–3.43at.%) alloys were investigated using flash method. Phase compositions and microstructure of Mg–La–Zn alloys were also analyzed using X-ray diffraction and scanning electron microscopy. Considering the thermal conductivity of single phase LaMg12 alloy and single phase τ1-(Mg, Zn)0.92La0.08 alloy measured in the present work, the thermal conductivities of Mg–La–Zn alloys in the two-phase regions (α-Mg+LaMg12 or α-Mg+τ1) were evaluated using the CALPHAD method. Results indicated that the Mg–La–Zn alloys with secondary phase (LaMg12) exhibited higher thermal conductivity than those with τ1, and the high solid solubility of Zn in α-Mg was detrimental to heat dissipation of Mg alloys. Meanwhile, the calculated thermal conductivities show good agreements with the corresponding experimental values.