Deformation structures and strengthening mechanisms in an Al-Mg-Sc-Zr alloy

The deformation structures, mechanical properties and strengthening mechanisms of an Al-5.4 Mg-0.4 Mn-0.2Sc-0.09Zr alloy subjected to equal- channel angular pressing (ECAP) for 12 passes at 573 K (300 degrees C) were studied. The yield stress (YS) increased gradually with increasing strain from 245 to 350 MPa, and the ultimate tensile strength (UTS) was nearly independent of the strain. An analysis of the strengthening mechanisms indicated that the increase in YS with the number of ECAP passes was attributable to increased contributions from dislocation and boundary strengthening. A "composite" Hall-Petch relationship, sigma(0.2) = 155+alpha MGb rho(1/2) +0.11 x d(GB)(-1/2) , where dGB is the distance between boundaries with misorientations of > 2 degrees, rho is the dislocation forest density, a is a constant, M is the Taylor factor, b is the Burger's vector, and G is the shear modulus, describes the effect of ECAP on the YS with a satisfactory accuracy. No change in the dispersion of the secondary phases during ECAP was observed; therefore, contributions from dispersion strengthening and solid solution strengthening to the overall YS were independent of the strain. (C) 2016 Elsevier B.V. All rights reserved.