Microstructure and precipitation in Al–Li–Cu–Mg–(Mn, Zr) alloys

Abstract

Hot rolled Al-6Li-1Cu-1Mg-0.2Mn (at.%) (Al-1.6Li-2.2Cu-0.9Mg-0.4Mn, wt.%) and Al-6Li-1Cu-1Mg-0.03Zr (at.%) (Al-1.6Li-2.3Cu-1Mg-0.1Zr, wt.%) alloys developed for age forming were studied by tensile testing, electron backscatter diffraction (EBSD), three-dimensional atom probe (3DAP), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). For both alloys, DSC analysis shows that ageing at 150°C leads initially to formation of zones/clusters, which are later gradually replaced by S phase. On ageing at 190°C, S phase formation is completed within 12 h. The precipitates identified by 3D atom probe and TEM can be classified into (a) Li-rich clusters containing Cu and Mg, (b) a plate-shaped metastable precipitate (similar to GPB2 zones/S''), (c) S phase and (d) δ' spherical particles rich in Li. The Zr containing alloy also contains β' (Al 3 Zr) precipitates and composite β'/δ' particles. The β' precipitates reduces recrystallisation and grain growth leading to fine grains and subgrains.

Predicting grain refinement by cold severe plastic deformation in alloys using volume averaged dislocation generation

“…Tensile tests were performed using an 8800 series Instron machine at a constant strain rate of 0.001 s -1 . Selected processing and microstructure data on the Al-Mg-(Cu)-Mn, Al-Cu-Mg and Al-Li-Cu-Mg alloys was reported before [38,39,40]. From the tensile test data K A (as defined in Section 3.2) was determined from the flow stress between 0.01 and 0.05 plastic strain.…”

Al–Mg–Cu based alloys and pure Al processed by high pressure torsion: The influence of alloying additions on strengthening

“…In these applications they derive their strength mostly from solution strengthening and strain hardening [13]. The Al-Mg-Cu alloys with higher Cu content (>2.5wt%) that are being studied in this work are applied predominantly in the aeronautical industry due to their in-service strength, which is due primarily to precipitation hardening [14,15,16,17], combined with good damage tolerance properties [18]. Recent development in these types of alloys has seen the introduction alloys with Li at relatively low levels (<2wt.…”

Editorial

“…This modified heat treatment can lead to superior mechanical properties, including fracture toughness, for a range of wrought alloys 48 and has been improved further by omitting re-aging after the lower temperature treatment 49 (whether this is commercially attractive remains to be seen). A good example of the benefits of a multi-technique approach is seen in Gao et al, 50 where various methods are used to study the precipitation sequence in AlLi-Cu-Mg alloys, with either Mn or Zr additions, subjected to multi-stage aging.…”