In order to clarify the yielding mechanism and the character of threshold stress for high temperature deformation of dispersion strengthened alloys, three kinds of Al-Mg-Mn alloys with different dispersion parameters were prepared. Their deformation behavior and threshold stresses were analysed by means of tensile and stress relaxation tests during the steady state deformation at strain rates from 3 × 10-5 s-1 to 3 × 10-3 s-1 at 673 K. Their threshold stresses were very close to the calculated Orowan stresses. The dependence of the threshold stress on the interparticle spacing was quite similar to the dependence of the Orowan stress. However, from the analysis of their deformation behavior and microstructure after deformation, it is found that the threshold stress is not determined by the Orowan mechanism but determined by the attractive interaction of dislocations with dispersed particles.
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