Microstructure mapping in friction stir welds of 7449 aluminium alloy using SAXS

Abstract

This paper describes the microstructural response of an age-hardenable, high-strength 7449 aluminium alloy to friction stir welding. Plates in the naturally aged (T3) and over-aged (T79) conditions were welded using two weld tool translation speeds. Maps of precipitate volume fraction and size were obtained by spatially resolved small-angle X-ray scattering over a cross-section of the welded plate, complemented by direct observations made by transmission electron microscopy. The spatial variations of precipitate volume fraction and size were assessed quantitatively for the characteristic zones of the welds, and supported by complementary hardness measurements. The effect of initial microstructure and welding speed, in particular in the heat-affected and thermomechanically affected zones, is discussed.

The strength of friction stir welded and friction stir processed aluminium alloys

“…Optimisation of strength of FS welds of heat treatable alloys can be sought with several complementary strategies. For example, minimizing the duration of the temperature spike (for instance by cooling of the weld or increasing welding speed) will generally increase the strength in the weakest section of the welds [36] both by limiting the time available for coarsening of phases and by reducing the time at the nose of the TTT diagram where detrimental precipitates form during cooling. Alternatively, we can attempt to modify alloy chemistry to provide precipitates that are more resistant to coarsening.…”

Coupled precipitation and yield strength modelling for non-isothermal treatments of a 6061 aluminium alloy

“…parabolic growth: R / t 1/2 ), which can give satisfactory results for isothermal treat- From the experimental point of view, transmission electron microscopy (TEM) has been widely used to validate or calibrate KWN-based models [5,6,12] because it provides information on the chemistry and morphology of precipitates. As far as volume fraction is concerned, small-angle X-ray/neutron scattering (SAXS/SANS) can be used as a complementary bulk analysis technique [19,7,21,22].…”

Characterising precipitate evolution in multi-component cast aluminium alloys using small-angle X-ray scattering

“…The Guinier approximation was used, since it is a well-established analysis method in metallic systems [12,15,17,19,26,27]. The precipitate parameter that can be extracted is called the radius of gyration (Rg).…”

“…AA2000 and 7000 series alloys) with low volume fractions of micron-sized constituent particles (i.e. those formed from Al and the impurity elements Fe and Si) [15][16][17][18][19][20][21][22][23][24][25][26][27]. Work on alloys that form a low volume fraction (~1 vol%) of trialuminide precipitates (dispersoids) has been limited to high purity Al-Zr-Sc alloys with ppm levels of Fe and Si [28,29], but not on casting alloy systems.…”