J. Phys. Colloques
Volume 48, Numéro C3, Septembre 19874th International Aluminium Lithium Conference
|Page(s)||C3-269 - C3-275|
J. Phys. Colloques 48 (1987) C3-269-C3-275
THE EFFECT OF GRAIN BOUNDARY PRECIPITATION ON THE SUPERPLASTICITY OF Al-Li ALLOYSH. YOSHIDA1, S. HIRANO1, Y. BABA1, T. TSUZUKU2 et A. TAKAHASHI2
1 Technical Research Laboratories, Sumitomo Light Metal Industries, Ltd., 1-12 3-Chome, Chitose, Minato-ku, Nagoya, 455, Japan
2 First Engineering Department, Nagoya Aircraft Works, Mitsubishi Heavy Industries, Ltd., 10 Oye-cho, Minato-ku, Nagoya, 455, Japan
The conditions of thermomechanical treatment to obtain superplasticity at high strain rate,~ 10-3 s-1 in 8090 ( Al-Li-Cu-Mg-Zr) and 2090 (Al-Li-Cu-Zr) alloys were investigated and the mechanism of superplasticity is discussed from the metallurgical point of view. It is found that 2090 alloy has excellent superplasticity in an as hot-worked condition compared with 8090 one. In 2090 alloy, the elongation in superplastic deformation increases with decreasing the temperature of hot working to 673K or less, at which temperatures substructures are developed during hot working by acceleration of precipitation. These substructures result in the formation of fine grains, during superplastic deformation. Whereas 8090 alloy has less superplasticity in an as hot-worked condition. In this condition, grain growth is apt to occur during heating or superplastic deformation. To obtain excellent superplasticity in 8090 alloy, it is necessary to homogenize at 793K and cold-work at the reduction of 90% in addition to hot working at a low temperature. This process stabilizes the substructures and inhibits recrystallization. Fine grains form by dynamic recrystallization. After the formation of fine grains, it is important to inhibit the grain boundary precipitation and grain growth in order to improve superplasticity further.