On the Mechanisms of Plastic Deformation of SAP-Type Alloys
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SAP-type alloys, which are obtained directly by powder metallurgy, consist of a dispersion of alumina particles in a polycrystalline aluminum matrix.
The kinetics of the deformation of these alloys has been studied by tensile tests. These tests, classical and differential, permit the determination of the activation energy and of the activation volume over a wide range of temperatures and stresses.
At low temperatures, from —196 to 20°C., the deformation mechanism is the thermally activated intersection of dislocations in the aluminum matrix. The density of dislocations increases rapidly with the strain and leads to high strain-hardening rates. At higher temperatures the dislocations move by cross-slip and by self-diffusion in the matrix. For temperatures above 350°C the apparent activation energy increases to very large values. Two models are proposed to explain this phenomenon: (1) a pinning of dislocations by the alumina particles; (2) reactions of attractive dislocations in those grains where there is still a high dislocation density. The grain size seems to have no influence.
KeywordsApplied Stress Apparent Activation Energy Activation Volume Pure Aluminum Alumina Particle
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