Magnesium Technology 2020: Thermomechanical Processing
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
Wednesday 8:30 AM
February 26, 2020
Room: 6C
Location: San Diego Convention Ctr
Session Chair: Christopher Barrett, Mississippi State University; Vineet Joshi, Pacific Northwest National Laboratory
8:30 AM Invited
Deformation Driven Precipitation in Binary Magnesium Alloys: Timothy Weihs1; Suhas Eswarappa Prameela1; 1Johns Hopkins University
Unlike Al alloys, precipitation strengthening of Mg alloys has proven challenging. Precipitate density is typically too low and precipitate size is often too large and elongated to enhance the resistance to plastic deformation significantly. Mimicking recent work in Al alloys, we are exploring how low temperature plastic deformation can enhance both the density, size, and morphology of common intermetallic particles and thereby lead to significant hardening in Mg alloys. The low temperatures tend to favor nucleation over growth while the deformation provides vacancies and dislocations that can assist nucleation. Using equal channel angular extrusion, simple compression, and moderate temperatures, we explore the processing and thermodynamic factors controlling nucleation and growth of precipitates in Mg-Al and Mg-Zn binary alloys and we compare the resulting intermetallic particles with those that are generated through conventional aging.
9:00 AM
Effect of Second Phase Particle Size on the Recrystallized Microstructure of Mg-Al Alloys Following ECAE Processing: Suhas Eswarappa Prameela1; Peng Yi1; Vance Liu1; Beatriz Medeiros1; Laszlo Kecskes1; Michael Falk1; Timothy Weihs1; 1Johns Hopkins University
Mg alloys are excellent candidates for structural applications, given their high strength to weight ratios. Grain boundaries and precipitates can both contribute to strengthening in Mg alloys, but the design of high strength Mg alloys is challenging due to Mg’s anisotropic crystal lattice and yield asymmetry. Herein, we focus on thermomechanical processing that involves grain refinement in the presence of precipitates. We seek an understanding of how small and large Mg17Al12 intermetallic particles impact recrystallization and discontinuous precipitation in Mg-Al alloys. We do so by processing solution-treated and peak-aged Mg-9Al (wt.%) alloys using equal channel angular extrusion (ECAE) along the 4Bc route at 150 oC. We find that the fine nano precipitates that nucleate within the solutionized grain interiors during ECAE processing lead to finer Mg grains in the recrystallization regions compared to those in the presence of the long lathlike precipitates produced during peak aging prior to ECAE processing.
9:20 AM
Relating Texture and Thermomechanical Processing Variables in Mg-Zn-Ca Alloys: Tracy Berman1; John Allison1; 1University of Michigan
It is well known that the strong basal texture that is commonly produced in magnesium alloy sheets leads to poor formability at room temperature. A sizable body of work has explored how changing the alloy composition and rolling conditions can yield more desirable textures. However important thermomechanical variables, such as the feed rate during rolling, are often not included in the literature, making it difficult to correlate how changes in processing affect the final crystallographic texture. This work explores the texture evolution and recrystallization behavior in Mg-Zn-Ca alloys during plane strain compression using a Gleeble thermomechanical simulator. This instrument allows for precise control and capture of the thermomechanical history of the sample. The texture and grain morphology of the compressed samples was then studied using Electron Backscatter Diffraction. The texture results are used to identify which alloys and processing conditions should be scaled up for future rolling studies.
9:40 AM
Variation of Extrusion Process Parameter for the Magnesium Alloy ME21: Gerrit Kurz1; Maria Nienaber1; Jan Bohlen1; Dietmar Letzig1; Kainer Karl Ulrich1; 1Magic-Magnesium Innovation Centre
Extrusion is an economic production process for the generation of semi-finished magnesium products that can be used for biomedical and automotive applications. This paper reports on the variation of process parameters (temperature and extrusion speed) in the aluminum-free magnesium alloy ME21 (2 wt% Mn and 1 wt% RE) during extrusion in order to investigate their influence on strength, ductility of the produced profiles. The influence of the varied process parameters on the microstructure before and after heat treatment is shown. Furthermore, the mechanical properties of the extruded profiles are presented and discussed with respect to arising textures. The results of this work are used to discuss how to tailor the mechanical properties of the magnesium alloy ME21 during the extrusion process.
10:00 AM Break
10:20 AM Invited
Fundamental Deformation Mechanisms During Solid Phase Processing of Mg Alloys: Suveen Mathaudhu1; 1University of California, Riverside
Magnesium alloys have shown enhanced properties when process through approaches where the liquid phase is avoided, i.e. solid phase processing (SPP). Technologies include methods such as friction stir processing /welding, friction extrusion, cold spray, shear assisted processing and extrusion (ShAPE) and others. This talk will present unique aspects of deformation and microstructural evolution that occur during SPP events, with a specific eye towards mechanisms promoting pathways to metastable states with enhanced properties.
10:50 AM
Asymmetric Rolling of TZ73 Magnesium Alloy to Improve Its Ductility: Krishna Verma1; Satyam Suwas1; Subodh Kumar1; 1Indian Institute of Science
Asymmetric rolling, i.e., upper and lower rolls having different circumferential speeds, is a novel technique to improve ductility of Mg alloys. A newly developed TZ73 Mg alloy was squeeze cast, homogenized at 300oC for 24 h, rolled at 350oC by symmetric and asymmetric rolling, and annealed at 215oC for 30 minutes. The microstructure was characterized by X-ray diffraction, scanning electron microscope equipped with energy dispersive X-ray spectroscopy and electron backscattered diffraction. A weakening of basal texture with a concomittent increase in ductility was observed for asymmetrically rolled sheet, while retaining the same strength as in symmetrically rolled sheet. Thus, tensile properties of 0.2% PS = 290 MPa, UTS = 332 MPa and El = 13% in hot-rolled, and 0.2% PS = 182 MPa, UTS = 282 MPa and El = 21% in annealed conditions were obtained for asymmetrically rolled sheet, which are extremely good for a rolled Mg alloy sheet.
11:10 AM
Friction Stir Processing of Magnesium Alloy with Spiral Tool Path Strategy: Abhishek Kumar1; Aarush Sood1; Nikhil Gotawala1; Sushil Mishra1; Amber Shrivastava1; 1Indian Institute of Technology Bombay
Friction stir processing is a relatively new technique for microstructural modification to improve the mechanical properties of materials. Previous works have been primarily focused on the processing of the small regions. The objective of this work is to study the effect of tool design, tool rotation direction and tool overlap between passes on the processed region. A spiral tool path strategy is employed to process the complete blanks of a Magnesium alloy. Three tool designs: tool with hexagonal, tapered and threaded pin are used. Further, tool rotation direction and tool overlap between passes are varied across the experiments. The material flow and defects formed in the processed region are characterized. Preliminary results show that tool rotation direction and tool overlap significantly affect the defects formed in the processed region. The present work identifies the processing condition for defect free processed region and refined microstructure of the Magnesium blank.
11:30 AM Invited
Joining Dissimilar Materials via Rotational Hammer Riveting Technique: Tianhao Wang1; Scott Whalen1; Piyush Upadhyay1; Keerti Kappagantula1; 1Pacific Northwest National Laboratory
Friction stir interlocking (FSI) and rotating hammer riveting (RHR) are emerging dissimilar material joining processes demonstrating hybrid features of mechanical fastening and lap welding, simultaneously. In these techniques, shear processing is used to integrate magnesium rivets/pins into a joint assembly. Riveting using magnesium was previously challenging owing to the its low workability at room temperature. In this presentation, an introduction to these processes and their advantages in joining metal and polymer plates will be demonstrated. Focus will be placed on the microstructural evolution of the components during processing and the micro-to-mesoscale features that are critical for ideal joint performance. Mechanical performance of FSI and RHR joints will be evaluated and contrasted with currently available industry standards. Finally, the importance of such processes in the context of developing reliable dissimilar high-specific-strength material joints for achieving lightweighting without compromising component performance and safety in the automotive industry will be presented.