Transmission electron microscopy on the microstructure of 7050 aluminium alloy in the T74 condition

The microstructure of 7050 aluminium alloy in the T74 condition has been investigated by transmission electron microscopy. It was found that the alloy contains the superlattice Al₃Zr phase, η′ phase and Al₇Cu₂Fe constituent phase. The η′ phase is proposed to have an orthorhombic crystal structure witha=0.492 nm,b=0.852 nm andc=0.701 nm. The orientation relationship between the matrix and η′ phase is [11−2]_m//[100]_η′; [1−]_m//[010]_η′;[−1−1−1]_m//[001]_η′. The phases on the small-angle grain boundary are found to be mainly η′ phase and Cu/Si-rich phase, whereas on the large-angle grain boundary there is only η phase.