Internal stress relaxation and load redistribution during the twinning–detwinning-dominated cyclic deformation of a wrought magnesium alloy, ZK60A

Abstract

A study of the internal strain (stress) evolution during cyclic deformation dominated by { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 1 〉 twinning and detwinning mechanisms within a magnesium alloy, ZK60A, was conducted using in situ neutron diffraction. It is shown that once the matrix grains twin, the (00.2) matrix and twin grains are relaxed relative to the neighbors. This load redistribution between the soft- and hard-grain orientations is a result of plastic anisotropy. The twins which formed during the initial compression sustain a tensile stress along the c-axis, when the applied compressive stress is less than ∼80 MPa upon unloading. This local (intergranular) tensile stress is hypothesized to be effective for driving the detwinning event under a macroscopic compressive field along the c-axis. The activation stresses, 15 and 6 MPa, respectively, for the { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 1 〉 extension twinning and detwinning, are approximated, based on the relaxation of the internal stresses in the matrix and twin grains.