Microstructure mapping of a friction stir welded AA2050 Al–Li–Cu in the T8 state

Abstract

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Microstructure distribution in an AA2050 T34 friction stir weld and its evolution during post-welding heat treatment

“…When studying the ageing kinetics, some T3W samples were also subjected to other ageing times at this temperature of 155°C from 0 h to 1000 h. Some results are finally compared to a weld realized with the same parameters, on a 2050T8 material, thus heat treated before welding. This last weld, called T8W, is described in detail in a previously published paper [26].…”

“…The SAXS patterns were interpreted following the same procedure as in [26]. Since the expected phases are either plate-like (essentially T 1 , GP-zones, h 0 ) or spheroidal (solute clusters), the signal has been interpreted as the sum of the contribution of spherical precipitates (of radii <10 Å) and flat cylinder particles.…”

“…Indeed, a large variety of precipitates can be observed in these alloys [13][14][15][16][17], from the Al-Li binary system (d 0 phase), from the binary Al-Cu system (GP zones, h 00 and h 0 phases), form the Al-Cu-Mg system for Mg-containing alloys (GPB zones, S 0 /S phases) and other phases from the Al-Cu-Li system (T 2 , T B ). Joining Al-Cu-Li alloys by friction stir welding has received some attention, both from the viewpoint of the resulting microstructure [18][19][20][21][22][23][24][25][26][27][28], mechanical properties [29][30][31][32][33] and corrosion behavior [34][35][36]. Most welded in the T8 temper, whose precipitate microstructure mainly consists of very thin platelets of T 1 particles and some h 0 as well as GP zones [9].…”

“…Depending on the welding conditions, the precipitate microstructure in the weld nugget has been shown to either consist of a population of T 1 , h 0 and T B particles [18,19], or of a full solid solution [21][22][23]. Intermediate zones (TMAZ, HAZ) consist of partially dissolved, coarsened T 1 precipitates, whose distribution have been mapped in the weld cross-section by spatially-resolved small-angle X-ray scattering (SAXS) [23,26]. Very little work has been devoted so far to Al-Cu-Li welds performed in the T3 state, although they show a very homogeneous hardness distribution [33].…”

“…More precisely, the aim is to understand the controlling parameters that explain the different levels of microstructure heterogeneity that develop during welding and during the post-welding heat treatments. For this purpose, we have performed systematic microstructure mapping by SAXS, which has been shown to be particularly powerful to obtain a complete view of the microstructure distribution in friction stir welds [4,6,23,26,37]. These microstructure maps have been compared to similar maps of microhardness, and complemented by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC).…”