Through-thickness heterogeneity and in-plane anisotropy in creep aging of 7050 Al alloy

Abstract

During creep aging (CA), through-thickness heterogeneity and in-plane anisotropy in creep and mechanical properties affect the shape forming and performance tailoring. The specimens are first machined from the surface (t1), subsurface (t2) and center (t3) layers along the thickness direction of the 7050 Al alloy plate. Then in the rolling plane of each layer, the specimens are taken along the angles of 0° (L0), 45° (L45) and 90° (L90) to the rolling direction. After CA, the creep strain shows the trends of t1 > t2 > t3 along the thickness direction and L45 > L90 > L0 for in-plane directions, while the yield strength (YS) shows t1 > t3 > t2 and L90 > L0 > L45, respectively.Before CA, the low-angle grain boundaries (LAGBs) increase along the thickness direction, leading to a reduced creep strain. After CA, through-thickness heterogeneous LAGBs contributes to the above trend of YS. After L45 and L90 loading, S, Brass and Copper textures are obviously weaker than that under L0 loading, and show the largest equivalent Schmid factor (ESF) for L45 loading, and that for L0 and L90 conditions are approaching; while the equivalent slip system number (ESSN) shows L90 > L0 > L45. Both ESF and ESSN determine the in-plane anisotropy by affecting dislocation slip, but ESF plays a dominant role.