1997 TMS Annual Meeting: Monday Abstracts

LIGHT WEIGHT ALLOYS FOR AEROSPACE APPLICATION IV: Session II: Al Alloys

Session Chairperson: W.E. Frazier, Code 4342, Naval Air Warfare Center, Patuxent River, MD 20670

THE DEVELOPMENT OF TEXTURE IN AlLi 2195 ALLOY DURING RING ROLL FORGING: Lan Zhang, Peter N. Kalu, Department of Mechanical Engineering, FAMUFSU College of Engineering, Tallahassee, FL 32310

This study presents results of texture and microstructural development in AlLi 2195 alloy processed by near-net-shape roll forging method. The manufacturing technique is a multistage process that combines conventional ingot conversion, back extrusion, and ring rolling to produce a heavy walled cylindrical forging preform. The preform is then rolled to nearfinal diameter using contoured rolling mandrels. A combination of optical microscopy, Orientation Distribution Function (ODF) and Orientation Imaging Microscopy (O1M) was used in this investigation. At the early stage of processing, (110) fiber texture was predominant. Following the second stage of processing, the texture was similar to characteristic fcc rolling texture. At the conclusion of processing, {001}<110> and {112}<110> shear components were developed at the expense of Brass ! component. The possible mechanisms responsible for the texture changes are discussed in relation with the microstructural evolution.

2:25 pm

ALLOY COMPOSITION EFFECT ON THE GLASS FORMING ABILITY AND THERMAL STABILITY OF THE Al86Mm4Ni10-xFex AMORPHOUS ALLOYS: H.W. Jin, Y.J. Kim, C.G. Park, Center for Advanced Aerospace Materials, Pohang Univ. of Sci. & Tech., Pohang 790784, Korea; M.C. Kim, Research Inst. of Industrial Science and Tech., Pohang 790600, Korea

Amorphous aluminum alloys show an attractive combination of high tensile strength and low density. The commercial applications of these alloys, however, have been restricted due to relatively poor thermal stability and glass forming ability (GFA). The GFA and the thermal stability of Al86Mn4Ni10-xFex alloys have been investigated with various alloy composition. Amorphous ribbons with the thickness from 20pm to 30µm were prepared by single roll melt-spinner. The microstructural evolution upon heating was observed by using X-ray diffraction and transmission electron microscopy (TEM). The GFA of the present alloys decreased with the increase of Fe content. However, the first (lowest) crystallization temperature, Txl, increased with increasing Fe content. The effects of alloy composition on the GFA and the thermal stability will be discussed in terms of the atomic bonding and electronic structure of the amorphous alloy.

2:50 pm

EFFECT OF STRETCHING PRIOR TO AGING ON MECHANICAL PROPERTIES AlCuLi (2195) ALLOY: Z.X. Li1, R A. Mirshams1, E.A. Kenik2, P.J. Hartley3 ;1Department of Mechanical Engineering, Southern University, Baton Rouge, LA 70813; 2Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831; 3Lockheed Martin Manned Space Systems, New Orleans, LA 70189

The Al-Cu-Li (2195) alloy was stretched uniaxially from 0% to 15% of plastic deformation prior to aging. The tensile properties of naturally and artificially aged specimens in 0, 45, and 90 degrees with respect to the pre-stretching direction were evaluated and their microstructures were characterized via TEM. The results indicated that the naturally aged specimen exhibited mainly ' (Al3Li) precipitates whose size appeared to be insensitive to pre-stretching. The moderate increase in yield strength by prestretching was attributed to work hardening effect. On the other hand, it was found that the precipitates of the artificially aged (at 180°C) specimen were primarily T1 (Al2CuLi) phase. The size of the T1 precipitates decreased with increasing amount of pre-stretching. A pronounced increase in yield strength by pre-stretching was observed with the presence of fine T1 precipitates. The relationship between mechanical properties and microstructures will be discussed. This work was sponsored partially by the Louisiana Board of Reagent and DOE-SHaRE program at Oak Ridge National Laboratory.

3:15 pm

CONTROL OF PROPERTIES BY RE (RARE EARTH METALS) ADDITION IN HIGH Mg CONTAINING Al ALLOYS: S.D. Park, J.H. Jung, H.K. Cho, Departments of Metallurgical Engineering, Kyungpook National University, Taegu 702-701, Korea

Recently, there is a great deal of interests in Al-Mg alloys due to their good combinations of strength and formability. To further improve their properties, high Mg containing Al alloys have been studied although serious problems associated with the precipitation of (Mg5Al8), such as low thermal stability and poor corrosion resistance, are generated with higher Mg concentration. In the present study, changes in precipitation behavior and mechanical properties by RE addition in high Mg containing Al alloys have been investigated. It has been shown that the precipitation of phase is restrained and mechanical properties are improved by RE addition.

3:40 pm

EFFECT OF COMPOSITION AND TEMPERATURE ON THE STRENGTH AND FRACTURE TOUGHNESS OF AL-CU-LI-AG ALLOYS: Cynthia L. Lach, NASA Langley Research Center, Mail Stop 188A, Hampton, VA 23681; Richard P. Gangloff, Department of Materials Science and Engineering, Thornton Hall, University of Virginia, Charlotttesville, VA 22903

The use of Al-Cu-Li-Ag-Mg-Zr alloys for fabricating aerospace vehicle components can potentially reduce system weight. For damage tolerant analysis, it is important to characterize and understand alloy strength and fracture toughness, particularly as affected by minor changes in composition and test temperature. The uniaxial tensile deformation, plane strain fracture toughness, and plane stress tearing resistance of two precipitation hardened alloys, AA2095 and AA2195, were examined as a function of Cu and Li levels and temperature from -185°C to 135°C. As temperatures decreased, the crack initiation toughness of AA2095 declined mildly while the toughness of AA2195 increased mildly. Alloy AA2195 demonstrated superior toughness in all cases. For each alloy the elastic modulus, yield strength and work hardening coefficient increased with decreasing temperature, while ductility declined from 135°C to -185°C. A plastic strain-critical distance-based micromechanical model utilized these properties to predict that KICI increased mildly with declining temperature for each alloy. The slope of this trend was in good agreement with measurements for AA2195, but less so far AA2095. In all cases fracture occurred without delamination and by microvoid nucleation, growth and coalescence involving second phase particles which were particularly large in the higher Cu/Li variant (AA2095). This difference, along with separate relationships between nearest-neighbor particle spacing and the critical microstructural distance from the model explain the higher toughness of AA2195.

4:05 pm

EFFECT OF Be ADDITION ON THE PRECIPITATION AND MECHANICAL PROPERTIES OF Al-Cu-Li-Mg-(Ag)-Zr ALLOYS: D. S. Chung, S. H. Cho*, H. K. Cho*, Dept. of Metallurgy, Changwon Industrial Master's College, Changwon 641772, KOREA ; * Dept. of Metallurgical Engineering, Kyungpook National University, Taegu, 702701

The effect of Be addition on the precipitation and mechanical properties of Al-Cu-Li-Mg-(Ag)-Zr alloys has been investigated by detailed transmission electron microscopy and hardness and tensile tests. It has been shown that the Be addition accelerates the aging response and improves the ductility while maintaining the strength of Al-Cu-Li-Mg-(Ag)-Zr alloys. Such improvements in mechanical properties are due to changes in precipitation behavior of Al-Cu-Li-Mg-(Ag)-Zr alloys by Be addition.

4:30 pm

MICROSTRUCTURAL EVOLUTION AND GRAIN DISTRIBUTION IN SUPERPLASTICALLY FORMED AlLi 8090 ALLOY: Peter N. Kalu, H. Garmestani, Department of Mechanical Engineering, FAMUFSU College of Engineering, 2525 Pottsdamer St., Tallahassee, FL 32310

With the advent of new analytical tools to study microstructures and microtexture, it is now necessary to re-characterize materials with complex structures. Using Orientation Imaging Microscopy (OIM), several microstructural parameters were obtained for superplastic Al-Li 8090 alloy deformed in tension. Grain orientation and distribution as well as the effective grain size based on standard definition of large angle grain boundaries were determined as a function of strain. The data was correlated with various models for superplasticity. The implications of the results on the deformation mechanisms operating during superplastic deformation is discussed.

4:55 pm

DISLOCATION STRUCTURES PRODUCED DURING HIGH TEMPERATURE DEFORMATION OF ALLI AA8090 ALLOY: W. Fan, M.C. Chaturvedi, Department of Mechanical and Industrial Engineering, University of Manitoba Winnipeg, Manitoba, Canada, R3T 2N2; N.C. Goel, N.L. Richards, Bristol Aerospace Ltd, Winnipeg, Manitoba, Canada, R3C 2S4

Deformation microstructures of an aluminum-lithium AA8090 SPF grade sheet have been studied by TEM. The alloy was deformed in tension at the superplastic deformation temperature of 530°C and at a strain rate of 1x10-3/sec. The tensile testing machine was fitted with a specially designed in-situ water quenching apparatus to preserve the deformation microstructure produced at the temperature of testing. The TEM thin foils were made from samples deformed and in-situ quenched from different strain levels. Most of the thin foils were prepared with the surface parallel to the through thickness cross-section of the sheet, rather than parallel to the rolling plane. Dislocation pairs and dislocation networks were observed in the deformed samples even when deformation was as large as 475%. The observed characteristics of dislocation configuration suggest that dislocation interactions take place during superplastic deformation, in which grain boundary sliding is considered to play a dominant role and the role of dislocations is mainly to accommodate grain boundary sliding. In this paper, the possible implications of dislocation interactions and the mechanism of superplastic deformation in aluminum-lithium alloy AA8090 are discussed.