New Yielding Phenomenon in Some Aluminium Alloys at High Temperatures

DOI Web Site 被引用文献16件 参考文献15件 オープンアクセス
  • Horiuchi Ryo
    Institute of Space and Aeronautical Science, University of Tokyo
  • Yoshinaga Hideo
    Institute of Space and Aeronautical Science, University of Tokyo
  • Hama Shigeo
    Institute of Space and Aeronautical Science, University of Tokyo

書誌事項

公開日
1965
DOI
  • 10.2320/matertrans1960.6.123
公開者
社団法人 日本金属学会

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説明

A new type yielding phenomenon was observed in Al-Mg and Al-Cu alloys which were pulled at high temperatures above about 350°C. In order to determine characteristics of this high temperature yielding phenomenon, several binary aluminium alloys were investigated by tensile tests at various temperatures from room temperature to 500°C and at various strain rates from 4×10−4 to 4×10−2 sec−1. The results were as follows: (1) This yielding was observed only in Al-Mg and Al-Cu alloys which were relatively large in the size difference between solute and solvent atoms, but it was not shown in pure aluminium and its alloys such as Al-Ag, Al-Li and Al-Zn which were relatively small in the atomic size difference. (2) This yielding was observed to occur from a lower temperature with the increase of the solute concentration and the decrease of the strain rate. (3) Work hardening after the yield drop was practically zero. (4) The stress drop in this high temperature yielding was not so rapid as those in usual yielding phenomena, but it proceeds relatively slowly. The pre-yield strain in this yielding was fairly large. (5) Under a condition where this type of yielding was observed,the flow stress was severely affected by the test temperature and the strain rate. The temperature and strain rate dependences of the flow stress can be expressed by the state equation<BR>\dotε=Aσnexp(−U0⁄kT).<BR>In Al-5.5 at% Mg, n=2,8∼3.3 and U0=1.4 eV. In Al-2.2 at% Cu, n=4.5 and U0=1.5 eV. (6) This yielding reappeared by annealing at the test temperatures. (7) No heterogeneous deformation related to this yielding phenomenon took place, the flow stress was independent of grain size.<BR>From these experimental results it may be concluded that under the condition where the high temperature yielding occurs, the plastic deformation is controlled by the viscous motion of dislocations which drag the solute atmosphere around them and thereby the increase in the mobile dislocation density during plastic deformation causes a remarkable yield drop, as proposed by Johnston.

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