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Session Chairperson: K. Jata, WL/MLLM, Wright Patterson Air Force Base, OH 45433
EFFECT OF PROCESSING VARIABLES ON MECHANICAL PROPERTIES OF RHEOCAST AZ9ID Mg ALLOYS: C.D. Yim, K.S. Shin, School of Materials Science and Engineering and Center for Advanced Aerospace Materials, Seoul National University, Shinrim-dong, Seoul, Korea
Rheocast ingots of an AZ9 ID magnesium alloy were produced with different processing conditions. Processing variables included stirring rate (Vs) and stirring temperature (Ts). The microstructures of the rheocast AZ9lD magnesium alloys were similar to those of composite materials consisted of soft primary particles distributed in the hard matrix. A detailed examination was made on the relation between processing variables and mechanical properties. With increasing Vs and Ts, the size and the solid volume fraction of the soft primary particles decreased and the hardness and the UTS of the rheocast alloys increased. The mechanical properties of the rheocast alloys were analyzed quantitatively as a function of microstructural parameters such as the size and the solid volume fraction of the primary particles.
DEFORMATION MECHANISMS AND MECHANICAL BEHAVIOR OF A NOVEL IN-SITU Be-Al COMPOSITE: X.D. Zhang1, J.M.K. Wiezorek1, G. Meyrick1, F.C. Grensing2, H.L. Fraser1, 1Department of Materials Science and Engineering, The Ohio State University, 2041 College Rd., Columbus, OH 43210; 2Brush Wellman, 14710 West Portage River South Rd., Elmore, OH 43416
There has been considerable interest in the production of light weight composite materials for aerospace applications. One of the promising candidates is an in-situ composite consisted of Be and Al. This material combines a high elastic modulus, low density with a relatively high melting point. Unlike the brittle Be, which does not undergo extensive plastic deformation prior to failure, the Be-Al alloys examined in the present study exhibit a remarkable formability. Both extruded and rolled products have been prepared successfully. However, the mechanisms responsible for these attractive characteristics of the Be-Al alloys have not yet been identified. Thus, it is timely and important to ascertain the active deformation modes governing the deformation charac teristics of Be when present in a continuous matrix of aluminum. Furthermore, it is necessary to examine the effect of the aluminum on the inhibition of initiation of cleave in the Be-Al alloys. In the present paper, we will present the results on the microstructural characterization of mechanically tested samples using SEM and TEM. The deformation behavior has been studied by SEM based fractography and TEM based on defects analyses. The observed fracture mechanisms will be discussed in terms of dislocation mobilities in the Al and the BE phase respectively.
EFFECT OF ALLOYING ELEMENTS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF SQUEEZE CAST MgAl ZnX ALLOYS: Jae Joong Kim, Do Hyang Kim*, Sang Hyuk Kim, Nack J. Kim, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790784, Korea, *Dept. of Metallurgical Eng., Yonsei Univ., Shinchondong, Seodaemunku, Seoul, Korea
Mg alloys offer the potential for significant weight savings in aerospace components because of their low density. Nevertheless, there is a strong need for Mg alloys with much improved mechanical properties. The main objective of the present research is to improve the mechanical properties of Mg alloys by squeeze casting and by alloy modification. The addition of Si results in the formation of Mg2Si in two morphologies; polygon and chinese script. While the polygonal Mg2Si improves the mechanical properties of Mg alloys, the chinese script Mg2Si promotes the brittle fracture along the Mg2Si/matrix interface, resulting in poor ductility. Microalloying elements have been added to modify the morphology of chinese script Mg2Si. It has been shown that the additions of Ca or P eliminate the chinese script Mg2Si so that all of the Mg2Si particles are present in polygonal form, resulting in the improvement of mechanical properties.
PHENOMENOLOGICAL MODELING OF SUPERPLASTICITY: F. Booeshaghi, H. Garmestani, P. N. Kalu, Department of Mechanical Engineering, FAMUFSU College of Engineering, Tallahassee, FL
There has been an increased interest in the mechanics and materials field to improve the constitutive relations for the superplastic deformation of advanced materials. This interest has been stimulated partly due to the discovery of high strain rate superplasticity, and partly due to the availability of powerful computers. In this paper, an attempt was made to develop new type of constitutive relations to elucidate superplasticity. Although the model was derived from Hart's model, it incorporates detailed microstructural parameters and can be extended to multiaxial deformation. An attempt was made to use the model to explain the deformation mechanisms in superplastic AlLi 7475 and Al-Li 8090 alloys. Load relaxation and jump strain rate tests were employed in this investigation. Microstructural characterization was carried out by optical nicroscopy and orientation Imaging Microscopy.
WATERJET ABRASIVE APPLICATIONS FOR LIGHT WEIGHT ALLOYS: Lin Zhong Lee, Laser Applications, Inc., Westminster, MD 21157
As the aerospace applications of light weight alloys expand, waterjet abrasive process is a viable approach to manufacturing. This technology utilizes high pressurized water and an abrasive passing through a nozzle that is capable of cutting most materials up to 9" thick. It provides precision cutting of any contour, shape, and size which will allow engineers and designers the freedom to create more complex designs. The main components of a waterjet system consist of an ultrahigh pressure intensifier, a cutting head, and a CNC controller. The jet parameters consist of the water pressure, orifice size, nozzle size, abrasive type, abrasive flow rate and cutting head feedrate. The kinetic energy is created from the mass of the water and abrasive exiting the nozzle at twice the speed of sound. At this high velocity, the jet stream acts like a solid medium that erodes the material. The efficiency of the waterjet is dependent on the initial energy leaving the nozzle and the energy required to remove the material. Therefore, it is easier to cut a soft and thin material than a hard and thick material. Through this process, superior edge quality is achieved with no heat affect zone (HAZ), no metal contamination, no distortion, no slag, and no delamination.
MICROMECHANICAL ANALYSIS OF ADHESION STRENGTH FOR A BRITTLE FILM COATED SUBSTRATE: Jeunghyun Jeong, HaeSeok Park, JeongHoon Ahn and Dongil Kwon, School of Materials Science and Engineering, Seoul National University, Seoul 151742, Korea
In this work, we attempted to estimate the interface adhesion strength through the stress analysis in a brittle film coated substrate by two methods: scratch method and film cracking method. Firstly, in a scratch test, the critical load used as a qualitative estimate of adhesion is converted into work of adhesion by analyzing the stress field beneath the indenter, which results from three contributions, i.e., the static indentation added by the blister stress field, the friction between the indenter and film, and the residual stress. Secondly, in uniaxial loading of a brittle film coated soft substrate, the adhesion dependency of the development behavior of the transverse film cracks is analyzed specifying the film tensile stress and the interface shear stress which induce film cracking and interface failure, respectively. Then, the interface adhesion is quantified as interface shear strength because the stoppage of film cracking with further straining means the interface failure by the excessive interface shear stress, and the saturated value of crack spacing and strain can be used for the qualitative comparison of adhesion.
ELECTROMAGNETIC PULSED CALIBRATION OF THIN ALUMINUM ALLOYS SHELLS: Sergey F. Golovashchenko, Moscow State Technical University, visiting at Ford Motor Company Scientific Lab Material Science Department, 20000 Rotunda Dr., P.O.Box 2053,MD3182, SRL, Dearborn, MI 481212053
Pulsed electromagnetic field have been used to size thinwalled shells inside calibration dies. This works even when the shell have been formed by bending sheet metal and closed by a welding seam. Deformation is accomplished by a highvoltage discharge of capacitors through a coil inside the shell. Experimental results for AlCuFeM high strength alloy rings are presented. They show a significant improvement of the accuracy of shell dimensions with increasing pressure amplitude. Results of the numerical simulation of the shell-die contact interaction are obtained assuming that shell is elastoplastic and the die is elastic. Solid mechanics equation of motion and elastoplastic flow rule have been used to simulate this process. This simulation takes account of multiple impacts, spring back, stress waves in shell and die and has been experimentally validated.
THERMAL ANALYSIS OF AGED BINARY Al-Li ALLOYS: Sedat Ozbilen, Gazi University, Faculty of Technical Education, Metal Educational Department, Teknikokullar, Ankara, Turkey
Al-Li binary alloys with nominal Li contents of 0.1, 1.0, 2.8 (in wt%) were aged naturally (for 3 months) and artificially (not only for 2 months both at 65% and 100°C but also for 2 days at 190°C) after water quenching to 25°C following solutionizing at 530°C for 20 minutes. Aging behaviour of these binary alloys were studied by Vicker's Hardness measurements and DSC/DTA thermal analysis. The results of this investigation will be presented.
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