Uniaxial and Biaxial Superplastic Deformations in Al Alloy

• Main Authors: Lee, Sei-Ching, 李詩欽
• Other Authors: Yang, Chih Fu
• Format: Others
• Language: en_US
• Published: 1994
• Online Access: http://ndltd.ncl.edu.tw/handle/17699442843449068000

碩士 === 大同工學院 === 材料科學(工程)研究所 === 82 === In this study the uniaxial superplastic (SP) roperties were examined and correlated to the biaxial gas blowing in a 7475 Al alloy. Results show that the biaxial forming behaviors predicted using materials parameters from uniaxial tensile tests agree well the experimental observations only for the low applied forming pressure, in which the effective flow stress as well as the corresponding forming strain rate are found to fall in the superplastic deformation range in most of its forming process. Anisotropy in superplastic behavior was studied using commercial available 7475 and 8090 Al alloys. The step-change variable pressure forming processes proposed in this study, which involve steps of isobaric forming with the strain rates kept within the superplastic region, not only can shorten the forming time spans for specific amounts of deformation, but also result satisfactory thickness profile. A significant improvement of forming efficiency has been demonstrated in the 3-step bulge forming process. Cavitation and the suppression of cavities in the 7475 Al alloy were examined. It was found that the superplastic formability in the 7475 Al alloy was improved by imposing hydrostatic back pressures. In addition, hipping eliminates the cavities of SPFed 7475 Al alloy effectively at 510℃ in half an hour.