The cyclic strain behaviour of crystals of aluminum-4 wt.% copper-i. the bauschinger effect

Abstract Single crystals of Al-4 wt. % Cu with a 〈112〉 axis, containing G.P. zones, or θ′', θ′' or θ precipitates, have been subjected to tensile flow followed by compressive flow at 293°K and 80°K, in an Instron modified to ensure axial strain and negligible hysteresis and back-lash. The Bauschinger effects observed have been analysed in terms of current theories of alloy strengthening. The results allow some assessment of the relative importance of the various proposed contributions to precipitation hardening in Al-4 wt. % Cu. It is concluded that most of the Bauschinger effect in crystals containing coherent precipitates can be accounted for by normal work-hardening in the matrix, but that there is a small additional effect associated with the disordering of G.P. zones. The very large Bauschinger effect which appears in crystals containing precipitates which are not coherent can be attributed to internal stresses continuing to build up at the particles during forward flow.