Morphologies, orientation relationships, and evolution of the T-phase in an Al-Cu-Mg-Mn alloy during homogenisation

摘要

The evolution of morphologies, orientation relationships (ORs), and twinning behaviours of the T-phase in Al-Cu-Mg-Mn alloys were investigated, during homogenisation at 485 degrees C for times ranging from 0.5 to 1000 h, by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). Results shows that the T-phase takes on a rod-like shape elongated uniformly parallel to the < 010 >(Al) direction. Four different shape categories of cross-sections of the T-phase (T-CSs) and three different types of ORs between the T-phase and Al matrix were identified. The T-CS has a clear relationship with the ORs of the T-phase. When the T-CS is a parallelogram (P) shape, the OR of the T-phase is OR-II, and an irregular-polygon (IP) shape, the ORs of the T-phase contain both OR-I and OR-II, while a shell (S) or decagon (D) shaped T-phases have all three ORs. During homogenisation, the P-shaped CS is gradually transformed to the IP-shape, followed by transformation to the S- or D-shapes. Anti-phase boundaries (APBs) along {101}(T) planes exist extensively in the T-phase, especially for that with a P- shaped CS. With the increase of homogenisation time, the number of APBs in the T-phase decreases and that of its T-twins increases. (C) 2017 Elsevier B.V. All rights reserved.