Magnesium Technology 2017: Solidification and Processing II
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
Wednesday 8:30 AM
March 1, 2017
Location: San Diego Convention Ctr
Session Chair: Norbert Hort, Helmholtz-Zentrum Geesthacht; Tracy Berman, University of Michigan
Processing of Mg-sheet via Twin Roll Casting: Dietmar Letzig1; Roland Hoppe1; Jonas Isakovic1; Gerrit Kurz1; 1MagIC - Magnesium Innovation Centre, Helmholtz-Zentrum Geesthacht
Twin roll casting (TRC) is an effective and therefor cost saving method for production of Mg sheet material. This is essential for widening the areas of application of magnesium especially in the automotive sector. Part of the ongoing project SubSEEMag which is focused on the substitution of rare-earth elements in Mg wrought alloys is the improvement of the TRC process. One problematic aspect of processing magnesium strip material in the TRC process is based on the temperature profile of the melt inside the tip. This could result in freezing of the melt inside the tip and its destruction. For resolving this problem various coated and non-coated ceramic materials were inspected regarding their thermal isolation capability and their durability in contact to molten Magnesium. For improving the flow behavior a new geometry of the tip was developed based on numerical simulations.
Effects of Mn and Zn Solutes on Grain Refinement of Commercial Pure Magnesium: Jian Gu1; Yuanding Huang1; Mingxing Zhang2; Karl Ulrich Kainer1; Norbert Hort1; 1Magnesium Innovation Centre, Helmholtz-Zentrum Geesthacht; 2School of Mechanical and Mining Engineering, The University of Queensland
The effects of Mn (peritectic system) and Zn (eutectic system) on the grain refinement of commercial pure Mg were investigated. Interdependence model and solute paradigm theory were applied to evaluate the grain nucleation and growth for these two alloy systems. Both Mn and Zn can refine the grain of pure Mg. Compared to Mg-Zn, the nucleant particles in Mg-Mn alloys are more potent, but the relatively activated number of nucleation sites is much fewer. Zn with relatively high value of growth restriction factor increases the initial rate of development of the constitutional supercooling (CS) zone at the earliest stage of grain growth, which plays a key role in determining the final grain size. Moreover, heavy segregation of Zn during solidification provides a driving-force to activate further nucleation in the CS zone, which may trigger some unknown native nucleation particles to sever as nuclei.
Experimental Investigation of Continuous Magnesium Production by Carbothermal Reduction: Boris Chubukov1; Scott Rowe1; Aaron Palumbo1; Illias Hischier1; Alan Weimer1; 1CU-Boulder
Magnesium production by carbothermal reduction (CTR) has the potential to significantly reduce operational costs relative to reduction by ferrosilicon or magnesium chloride electrolysis. As magnesium is gaseous at CTR reaction temperatures the challenge remains effective separation of magnesium vapor and CO by-product, which can recombine unproductively. Our preliminary investigations focused on carbothermal kinetics and magnesium yield in batch reactions at isothermal and isobaric conditions. To simulate continuous production, magnesium metal was boiled in a thermogravimetric system and mixed with CO in a tubular condenser. Monitoring of the CO signal by IR allowed for determination of the extent of reversion, and analysis of deposits revealed the purity of the product Mg. The effect of pressure and temperature were investigated in both systems. Based on these results a continuous moving bed condenser was fabricated to determine the feasibility of vapor product capture from CTR.
Grain Refinement of Mg-Gd-Y-(Zr) Alloys through Squeeze Casting: Cunlong Wang1; Kaka Ma2; Enrique J. Lavernia2; Guohua Wu1; Wencai Liu1; Wenjiang Ding1; 1Shanghai Jiao Tong University; 2University of California, Irvine
The Mg-10Gd-3Y (GW103) alloy and Mg-10Gd-3Y-0.5Zr (GW103K) alloy were successfully fabricated by squeeze casting (SC) under various applied pressures. The results show that grain size of both alloys was gradually refined through increasing the applied pressure. The grain refinement effect in the Zr-free alloy is limited, while the grain refining effect can be enhanced by combined applying of pressure and addition of Mg-Zr master alloy. Tensile test results show that both the yield strength and ultimate tensile strength are increased for both alloys when increasing the applied pressure. The strength enhancement for squeeze cast Mg alloys were mainly ascribed to the refinement of grain size and reduction of micro-pores.
Precipitation Behavior of Mg-Al-Sn-Zn(-Na) Alloys: Sumi Jo1; Yohan Go1; Kwang Seon Shin2; Bong Sun You3; Young Min Kim3; 1Korea University of Science and Technology; 2Seoul National University; 3Korea Institute of Materials Science
Mg-Sn-Zn(-Na) alloys (Sn: >8wt.%) with high yield strength were recently developed via extrusion process. According to previous results, Sn is known as a strong precipitation hardening element through the formation of fine Mg2Sn precipitates, and the dilute addition of Na can promote precipitation kinetics for Mg2Sn and increase their number density by means of providing Sn-Na clusters. In contrast, however, the role of Sn in Mg-Al-Zn-Sn system, of which major second phase is Mg17Al12, has not been clearly understood, and furthermore the effect of Na is still questionable in high-Al containing alloys. In the present study, therefore, we investigated the effect of the addition of Sn or Na on precipitation behavior of Mg-Al based alloys. The results of TEM analyses showed that in Mg-Al-Sn-Zn alloys (Al: 6~8wt.%) Mg17Al12 precipitates formed first inside grains during artificial aging treatment provided nucleation sites for Mg2Sn. Detailed results will be shown at the presentation.
10:10 AM Break
Study on the Direct Oxidation Thermal Decomposition of Magnesium Chloride Byproduct in the Sponge Titanium Production Process to Prepare Magnesium Oxide: Liping Niu1; Zhang Ting'an1; Guozhi Lv1; Aiping Zhou1; 1Northeastern University
The companies sell the molten MgCl2 as a kind of waste at low price after cooling. This causes the waste of resource and energy. A new method named of “situ pyrolysis of molten magnesium chloride”was proposed to solve this problem. The molten MgCl2 produced by vacuum distillation in magnesium thermal reduction process was treated by the direct oxidation thermal decomposition method to produce ultrafine MgO with high purity and chlorine gas. The magnesium produced by thermal reduction of MgO can return to the boiling chlorination of high titanium slag. So, the new cycle of magnesium and chloride in titanium sponge production can be achieved. Based on the thermodynamic analysis of the gas phase reaction between O2and MgCl2, this paper contains the single factorexperiments. The optimal reaction condition was determined and the impact of each factor on the pyrolysis process was studied
Thermal Decomposition Kinetics of Pre-prepared Pellets for the Novel Silicothermic Process: Lukui Guan1; Zhang Ting'an1; Zhihe Dou1; Daxue Fu1; Ming Wen1; 1Northeastern University
A novel silicothermic process was put forward in order to solve the problems in Pidgeon process, including a loss of five percent fine powder produced during the calcination of dolomite and the easily deliquescence for calcined dolomite. For this method, pre-prepared pellets, which consist dolomite, ferrosilicon, fluorite and binder, are prefabricated before calcination, and then the calcined pellets are used directly for magnesium production. The difference of decomposition behavior and thermal decomposition kinetics between pre-prepared pellets and pure dolomite have been studied by thermogravimetry (TG) and differential thermal analysis (DTA) under non-isothermal conditions at different heating rates (4, 8, 16, and 30K/min). The thermal decomposition data were analyzed using some isoconversional methods. The decomposition temperature of pre-prepared pellets was lower than pure dolomite due to the higher thermal conductivity of ferrosilicon. The activity energy of decomposition of dolomite in pre-prepared pellets was lower than pure dolomite.
Thermal Stability of Cryomilled Mg Alloy Powder: Dikai Guan1; Mark Rainforth1; Joanne Sharp1; Junheng Gao1; 1University of Sheffield
In this paper, the thermal stability of cryomilled nanocrystalline AZ31 powder was evaluated by annealing at elevated temperature ranging from 350 °C to 450 °. There were two separate growth stages with a transition point at around 400 °C. More specifically, between 350 and 400 °C, NC Mg grains were stable at approximately 32 nm, even after 1h annealing. At 450 °C, the nano grains grew to 37 nm in the first 5 minutes and grew quickly to approximately 60 nm after 15 minutes. However, the grain growth was limited when the annealing time was increased to 60 minutes. The average grain size remained stable less than approximately 60 nm even after long anneals at temperatures as high as 450 °C (0.78 T/TM), indicating an outstanding degree of grain size stability. This excellent thermal stability can be mainly attributed to solute drag and Zener pinning.
Thermomechanical Processing of Thixomolded Alloys: Raymond Decker1; Stephen LeBeau1; Tracy Berman2; Tori Miller3; Wayne Jones2; Tresa Pollock4; Nir Moskovich5; Boris Bronfin5; 1Thixomat, Inc/nanoMAG LLC; 2Univ of Michigan; 3North Carolina State University; 4Univ of California Santa Barbara; 5ICL Magnesium
A wide variety of Mg alloys have been processed by Thixomolding® followed by thermomechanical processing (TMP) - to increase tensile, creep and fatigue strength, ductility and formability. These alloys encompass variations in Al, Zn, Ca, Mn, Sr, Y, Zr and Rare Earths (RE) in the Mg base. Due to the fine microstructure and low porosity rendered by Thixomolding, TMP has been feasible using high strain warm rolling and warm pressing. Thus, grain size is further reduced and texture can be moderated. Data will be presented on the above alloys along with more extensive information on the commercial alloys AM60 and AZ61; but also the newly developed AZ70L-TH and AXJ810-TH alloys. Friction stir welding, to join Thixomolded plates before TMP, afforded larger final sheet sizes. In discussing the above processing, properties will be related to microstructures. This research was sponsored by NSF STTR Project No. 0847198 and BIRD Foundation Contract 1243.