Influence of Fe-rich phases and precipitates on the mechanical behaviour of Al-Cu-Mn-Fe-Sc-Zr alloys studied by synchrotron X-ray and neutron

Abstract

A multiscale methodology using scanning and transmission electron microscope, synchrotron X-ray nano-tomography and micro-tomography, small angle neutron scattering, and in situ synchrotron X-ray diffraction has been used, to reveal the effect of Fe-rich phases and precipitates on the mechanical behaviour of an Al-Cu-Mn-Fe-Sc-Zr alloy. The α-Al grains size is reduced from 185.1 μm (0 MPa) and 114.3 μm (75 MPa) by applied pressure. Moreover, it has been demonstrated that suitable heat treatments modify the 3D morphology of Fe-rich phases from interconnected to a disaggregated structure that improves the mechanical properties of the alloy. The size and morphology evolution of fine precipitates under different ageing temperature and time are revealed. At ageing temperature of 160 °C, the precipitates change from GP zones to θ' (around 75 nm in length) with ageing time increasing from 1 h to 24 h; the Vickers hardness increases from 72.0 HV to 110.7HV. The high ductility of the Sc, Zr modified Al-Cu alloy is related to the complex shape and the loss of interconnectivity of the Fe-rich particles due to the heat treatment. The evolution of the crystal lattice strains in α-Al, and β-Fe calculated during tensile test using in-situ synchrotron X-ray diffraction corroborates the influence of the microstructure in the ductility of the modified alloy.