A weak texture dependence of Hall–Petch relation in a rare-earth containing magnesium alloy

Abstract

• The Hall–Petch slope k of a RE-containing Mg alloy shows a texture-independence. • The weak texture dependence of k is related to the activation of additional deformation mode. • The previously developed equation k = 2 σ d m ′ − 1 r 1 / 2 can predict the texture independence of k . Hall–Petch slope ( k ), an important parameter in Hall–Petch relation, describes the efficiency of strengthening effect by grain boundaries. Previously, a highly texture dependent k for Mg alloys is frequently reported, but, in the present study, we report a weak texture dependence of k in a rare-earth containing Mg-2Zn-1Gd plate with two peaks of (0002) poles inclining approximately ± 30 ° away from the ND toward the TD. Although there is a strong mechanical anisotropy between tension along the TD and RD, the k for TD-tension (280 MPa μm 1/2 ) is quite similar to that for RD-tension (276 MPa μm 1/2 ). Here, RD, TD and ND refer to the rolling direction, transverse direction and normal direction of the plate, respectively. The weak texture dependence of k is well predicted by the compound use of the activation stress difference between neighboring grains (ΔStress) and the geometric compatibility factor ( m ′ ). By analyzing how the texture affects the values for ΔStress and m ′ , the mechanism for this texture independence of k is ascribed to the activation of a high fraction of additional deformation mode, besides the predominant one for both RD-tension and TD-tension, namely, prismatic slip accompanied by a high fraction of basal slip for RD-tension and basal slip accompanied by a high fraction of prismatic slip for TD-tension. This will lead to multiple deformation transfer modes and, consequently, the effect of texture on the ease of deformation transfer across grain boundaries is weakened. As a result, there is a similar k for TD-tension and RD-tension.