Tension characteristics of notched specimens for Al-Li-Cu-Zr alloy sheets with various cerium contents
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I.
INTRODUCTION
THE A1-Li based alloys have the prospect of applications in aircraft structures to reduce the structural weight. However, these alloys must achieve an acceptable balance of engineering properties, at least equivalent to those of aluminum alloys,tq Unfortunately, by comparison with conventional aluminum alloys, the present generation of A1-Li based alloys still has some unsatisfactory sides in engineering propertiesY 7] Therefore, for widespread application of A1-Li based alloys in aircraft structures, particular attention has been paid to improvements in their engineering properties. Some trace elements or rare earth elements such as cerium, scandium, and lanthanum could be utilized as the beneficial alloying additions in A1-Li based alloys to improve their microstructures and mechanical properties38-~9~ If an AI-Li based alloy modified by microalloying of rare earth elements is intended for practical applications in aircraft structures, the behavior of the alloy in the presence of high stress concentrations must be understood because the cracks often start at the places of stress concentrations such as fastener holes, whose presence is usually unavoidable in practical structures such as fuselage skins or wing skins. It is known that the notch strength (O'x) may be utilized as a measure of mechanical behavior under stress concentrations for a metallic material, and it has played an important role in conventional aluminum alloys.t20.2~.221 Accordingly, accompanied with the damage tolerance engineering properties such as fatigue resistance and fracture toughness, crN should be also taken as an important parameter for the quality control in the products made up of the A1-Li based alloy L. MENG, Associate Professor, and X.L. ZHENG, Professor, are with the Department of Materials Science and Engineering, Northwestem Polytechnical University, Xi'an, 710072~ People's Repubhc of China Manuscript submitted July 18, 1995. METALLURGICALAND MATERIALSTRANSACTIONS A
contained with the rare earth elements. However, the effect of the rare earth modification on the stress concentration characteristics or notch strength for AI-Li based alloys under monotonic tensile loading, to the best of the authors' knowledge, has not been investigated and reported in the open literature, although the results of preliminary research on the notch strength of alloy 2090 t231 and some notch fatigue tests for some of the modem A1-Li based alloys have been reported. {~~ It is therefore the objective of the present study to examine the stress concentration sensitivity for a high strength A1-Li-Cu-Zr sheet alloy containing various contents of a rare earth element, Ce, by means of the monotonic tensile test to the notched specimens of different K, values. The test results have been also quantitatively analyzed to give an expression for predicting the notch strength of the A1Li-Cu-Zr alloy sheets by Ce modification.
II.
EXPERIMENTAL PROCEDURES
A. Preparation of Test Materials The test materials were melted in a vacuum induction furna
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