In order to investigate the effect of grain size, tensile tests were performed for Al-7 mass%Mg alloys having various grain sizes.
Results obtained are as follows:
(1) In the lower temperature range, the activation energy for onset of serrated yield is found to be about 23 kJ/mol and does not depend on the grain size.
(2) In the relatively high temperature range, strain for onset of serrated yield (ε
c) becomes larger with rising temperature in the grain size range from 20 to 800 μm.
While, in the specimen having 1300 μm of grain size, serrated yield occurs at an early stage in the plastic deformation, and the value of ε
c is almost independent of deformation temperature.
In the grain size range from 20 to 400 μm, the relation between grain size (d) and stress (σ
c) required for the onset of serrated yield is expressed as follows:
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\
oindentwhere σ
0 is a frictional stress of mobile dislocation and
Kc is a constant.
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