1997 TMS Annual Meeting: Tuesday Abstracts

SYNTHESIS OF LIGHT-WEIGHT METALLIC MATERIALS II: Session III: Metallic Composites III: Alloying, Thermomechanical Processing and Microstructural Control

Session Chairpersons: D. Tsakiropoulos, Dept. of Materials Science and Engineering, University of Surrey, Guildford, Surrey, GuZ 5XH, UK; D. Upadhyaya, University of Idaho, Institute for Materials and Advanced Processes, Mines Bldg 204, Moscow, ID 83844-3026

8:30 am

THERMODYNAMICS OF VACUUMTHERMIC REDUCTION OF LIGHTWEIGHT MAGNESIUM-LITHIUM ALLOY: Dajian Wang, Department of Metallurgy, Kunming University of Science and Technology, Kunming, Yunnan 650093, China

The principles of preparation of light weight alloy of Mg-Li alloy with a low-density less than 1g/Cm3 with vacuumthermic reduction are described according to the preliminary laboratory-scale results. The process involves the use of ferrosilicon and aluminium to reduce magnesia and lithium oxide concurrently in a vacuum furnace to mixing gas of metallic magnesium and lithium due to the higher pressures for both magnesium and lithium. The metallic vapours are cooled at the lower temperature part of the furnace. Thermodynamic analysis of related reactions and their equilibrium constants revealed the probabilities of reactions and preferable reductants of ferrosilicon or aluminium. The alloying effects at low pressure of reduced magnesium and lithium and their evaporation may significantly dominate the progress of the process. Based on the calculation determination of activity coefficients of components in Mg-Li binary, the thermodynamic aspects for both reduction process and vaporisation process are systematically analysed in the paper.

THE FOLLOWING PRESENTATION IS WITHDRAWN
8:50 am

STRESS RELIEVING METHODS FOR THICK ALUMINIUM ALLOY PLATE: EVALUATION BY X-RAY DIFFRACTION RESIDUAL STRESS MEASUREMENT: Bernt Jaensson, CSM Materialteknik AB, Box 13200, S-58013 Linköping, Sweden; Alfred Heinz, Hoogovens Aluminium Walzprodukte GmbH, Postbox 920, D-56009 Koblenz

In the design of metallic structural parts for aircraft there are, basically, two approaches that can be taken: either the part is built up from a number of individually formed elements which are joined by riveting or adhesive bonding, or the part is sculptured from a single forging or piece of plate. In this situation, designers of small aircraft tend to use the first approach, while integrally machine parts are dominant in the structure of large aircraft. However, the balance between the two options is also changing with time, in that present-day aircraft engineers are increasingly favouring the sculpturing method. Contributing to this trend is the availability of numerically controlled high-speed milling machines, as well as forgings and plate with low levels of residual stress. The choice between a hand forging/die forging or plate is often dictated by the height of the final part. Since plate can be more efficiently stress relieved - by stretching - it is the preferred choice whenever the thickest available plate can accommodate the part. In the last couple of years, plate producers have strived to raise the upper limit of the thickness range from, say, 150 mm to 250 - 300 mm. In so doing, might exceed the capacity of existing stretching presses, which necessitates the use of an alternative stress-relieving method e.g. stepwise cold compression. With respect to the resulting residual stress level, one could ask the question to which extent the relative advantage of plate over forging is preserved in this case. An earlier investigation of the relationship between stress-relieving of die forgings, residual stresses and distortion during machining is recapitulated to give a background to the present work, which involves measurement of through-thickness stress variations in 100 and 150 mm thick plate, stress relieved by stretching, and in cold compressed plate of 200 mm thickness.

9:10 am

TEXTURE CONTROL OF ALUMINUM ALLOY SHEETS: C.-H. Choi, K.-H. Kim, D.N. Lee, School of Materials Science and Engineering and Center for Advanced Materials Research, Seoul National University, Shinrimdong, Kwanak-ku, Seoul 151-742, Korea

In order to achieve good deep drawability it is imperative to obtain well developed {111}texture which gives rise to the higher plastic strain ratio. It is difficult to obtain the texture from conventional rolling and annealing processes. Therefore an unconventional rolling process which causes shear deformation has been introduced in addition to the conventional rolling process. Various combinations of the conventional and unconventional rolling processes and the annealing process have been theoretically and experimentally studied to obtain the well developed {111}texture which in turn gave rise to a substantial increase in the plastic strain ratio.

9:30 am

THERMO-MECHANICAL BEHAVIORS OF Al-Ni-Mm AMORPHOUS ALLOYS: S.J. Hong, H.S. Kim, C.W. Won, S.S. Cho, B.S. Chun; Department of Metallurgical Engineering and RASOM, Chungnam National University Kung-dong, Yuseong-gu, Tacjeon 304-750, KOREA; P.Warren, B. Cantor, OCAMAC, Department of Materials University of Oxford Parks Road, Oxford, OX1 3PH, UK

The Al-M-Mm (Mm=misch metal) alloys have been produced by a gas atomization, a sing roll melt spinning and a twin roll spinning methods. These alloys have amorphous structure, finely mixed structure consisting of aluminium phase, intermetallic compounds homogeneously embedded in the ultrafine "rained aluminium matrix and intermetallic compounds in the large "rained aluminium matrix depending on the process variables. The alloy powders and ribbons have been warm compacted to various relative densities at various temperatures. The cylindrical and ring shapes compacts have been upsetted at various temperatures and the plastic deformation behaviours have been investigated using TEM, DSC and XRD. The density distribution, load, deformed geometry, friction coefficient, interparticle bonding behavior have been compared with the theoretically calculated ones. The forming limit diagrams have obtained from the ring compression tests.

9:50 am

MICROSTRUCTURES AND MECHANICAL PROPERTIES OF AZ91 AND AM60 MG ALLOYS BY TWIN ROLL PROCESS: S.S. Cho, B.S. Chun, C.W. Won, B.S. Lee, H. Baek, K.H. Yim, Department of Metallurgical Engineering and RASOM, Chungnam National University Kung-Dong, Yusong-gu, Taejon 304-750, KOREA F.H. Froes, Institute for Materials and Advanced Process, University of Idaho, Mines Building, Room 321 Moscow, Idaho 83844-3026

It is well known that Mg alloys are quite attractive for structural use in aerospace and automotive industry due to the light weight. The properties of RS AZ91 and AM60 Mg alloys by twin roll cast will be compared with commercial ingot metallurgy alloys. The process including flake production, degassing, cold compaction and hot consolidation will be discussed. The Corrosion behavior will be also discussed.

10:10 am BREAK

10:30 am

MECHANICAL PROPERTIES OF Mo-Al ALLOYS BY TWIN ROLL PROCESS: S.S. Cho, B.S. Chun, C.W. Won, S.D. Kim, B.S. Lee, H. Baek, Department of metallurgical Engineering and RASOM, Chungnam National University Kung-Dong, Yusong-gu, Taejon 304-750, Korea; F.H. Froes, Institute for Materials and Advanced Process, University of Idaho, Mines Building, Room 321 Moscow, Idaho 83844-3026

Rapid solidification processing(RSP) has been exploited to improve mechanical properties of materials. This study will focus on the process including the production of flake by twin roll cast, degassing, cold compaction and hot extrusion. The properties of experimental Mg-AI alloys are compared with ingot metallurgy alloys. The corrosion and wear behavior will be discussed.

10:50 am

NUMERICAL ANALYSIS OF MICROSEGREGATION IN AL ALLOY WELD METALS: C.H. Lee, E.P. Yoon; RASOM, Dept. of Met. Eng., The Hanyang University, Seoul, Korea, 133-791

During solidification of alloys under rapid thermal excursion of welds, the solute redistribution brings out microsegregation. The microsegregation causes the formation of non-equilibrium second phases, shrinkage and porosity degrading properties and forming solidification crack. Therefore, it has been required to predict microsegregation quantitatively. To predict the degree of microsegregation, more exact and appropriate computer simulation technique has been being actively used during last two decades. In this study, an advanced two dimensional model was suggested on the basis of the previous one and two dimensional models. In the new model, both primary and secondary arm regions were defined for the analysis region. Before calculation of microsegregation, the analysis region was determined by the theoretical equation for the primary and secondary arm spacing. The growth in the primary arm region was assumed to be a planar for effective calculation. Especially, for the growth of a secondary arm, a simple and effective mathematical function was established to show the growing pattern(polynomial interface). The solute diffusion in the solid phase was calculated by finite difference method (FDM). The solid-liquid interface movement was considered to be in local equilibrium state indicated by the phase diagram.

11:10 am

PHASE STABILITY OF Ab66Mn9(Ti, Zr)25-DISPERSION-STRENGTHENED Al ALLOY: Seung-Zeon Han, Seong I. Park, Seon-Jin Kim, Hyuck-Mo Lee, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Kusung-Dong 373-1, Yusung-Gu, Taejon, Korea 305-701; Department of Materials Engineering, College of Engineering, Hanyang University, Hacngdang-Dong 17, Seongdong-Gu, Seoul, Korea 133-791

The addition of Mn to the tetragonal Al3(Ti1-xZrx) phase produced cubic Ll2-type Al66Mn9(TiZr)25 phase with a small amount of second phases such as Al8Mn5 and Al2Zr, still existing in the as-cast state. Second phases disappeared when intermetallic compounds were homogenized at 1000°C for 24 hours. After homogenization, intermetallic compounds were mixed with pure A1 in the form of powder by attritor mill and then vacuum hot pressed. IDS (intermetallic-dispersion-strengthened) Al alloys prepared in this way were analyzed in terms of phase stabilities and microstructures through XRD, SEM and TEM methods.

11:30 am

EFFECTS OF MICROALLOYING WITH Ce, Ni AND Si ON THE BEHAVIOUR OF INGOT ALUMINIUM ALLOY: C912 (A1-Zn-mg-Cu): Y.L. Wu, G.G. Li, F.H. Froes and J. Liu, BIAM, PO Box 81, Beijing 100095, China; IMAP, University of Idaho, Moscow, Idaho 83844-3026; Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069-0001

The present paper will discuss the effects of microalloying with Ce, Ni and Si on the behaviour of the ingot aluminium alloy C912 (A1-9Zn-2Cu-2Mg). The relationship between the chemistry, processing, microstructure and mechanical behaviour will be present for direct chill cast ingots which were subsequently extruded. Preliminary results show that this alloy class can exhibit attractive combination of strength and corrosion resistance.

11:50 am

SOLIDIFICATION PROCESSING FOR THE PRODUCTION OF FINE GRAIN ALUMINUM ALLOY MATERIALS: Akira Sato, Garo Aragane, Yoshiaki Osawa, and Susumu Takamori; National Research Institute Far Metals, Tsukuba, Ibaraki 306 Japan

It is well-known that metallic materials having fine grain crystal structures possess high mechanical properties, ie., high strength and at the same time high toughness. A new process named "Rapid solidification with vigomus agitation" is developed to produce large ingots having fine grain and homogeneous structures. The molten alloys are rapidly solidified with watercooled copper molds and at the same time stirred vigorously by graphite rods during falling down of the melt through the gap between the mold and the rod. The results obtained using Al-Si alloys are as follows. The mean grain size of primary crystals in slurry become smaller with increasing the intensity of cooling and the rotation speed of stirring rod. Primary and eutectic Si grains are not only small but also globular when the agitation is strong enough.