Work hardening by deformation induced vacancies in low temperature deformed aluminium single crystals

Al-monocrystals with single slip orientation of two different purities were deformed at 77 K by a certain prestrain γ, arriving at a resolved shear stress τ (strengthening coefficient Θ). Then the crystals were annealed at Ta = 293 K for different annealing times and re-deformed at 77 K, in order to study the effect of annealing to the new resolved shear stress τa (strengthening coefficient Θa). Anomalous maxima could be observed in the isotherms of (τa −τ), Θa/Θ which shift to smaller annealing times with increasing γ, but to larger ones with increasing impurity content. By comparing these results with those from quenched samples, and with isochrones of electrical residual resistivity performed in parallel, it is concluded that the anomalous hardening effects arise from vacancy agglomerates being formed during deformation, similarly to Cu and Zn previously studied by the authors.