Kinetics of the portevin-le chatelier effect in Al 6061 alloy

Tensile tests were performed on commercial Al 6061 alloys using a tensile system designed to minimize its mechanical resonances. Strain in the test alloys was measured with a fast-response capacitance strain transducer. Plastic strain bursts exceeding the imposed elongation rate of 0.83 μm/s were detected between 273 and 373 K. These bursts produced stress serrations of types B and C on the load-elongation curves. The magnitudes of the types B and C serrations for long aging times were found to have the same analytic dependence on stress, strain, and work hardening. The durations of the type B and C strain events obey the same Arrhenius expression with activation energy of 0.6 eV. The difference between type B and C serrations arises from the plastic deformation occurring between the abrupt strain events. The serrations are attributed to a collective motion of dislocations where the rate-controlling process is the cutting of forest dislocations by moving dislocations that have become free of segregated solutes. The disappearance of the stress serrations for T < 273 K is caused by the slowness of the segregation of solutes to momentarily arrested dislocations. The disappearance of the serrations for T > 373 K occurs because the imposed deformation rate can be accommodated by a population of solute-dragging dislocations.