Effects of homogenisation treatment on microstructure and hot ductility of aluminium alloy 6063

Abstract

Several homogenisation treatments were applied to direct chill (DC) cast ingots of aluminium alloy 6063, in order to analyse the resulting microstructures developed from these diverse conditions and their effects on the hot ductility of this alloy. Imaging was performed using scanning electron microscopy (SEM) and a focused ion beam (FIB) instrument. These techniques identified variations in distribution and morphology of second phase particles (AlFeSi and Mg 2 Si). FIB results for the various AlFeSi particles correctly identify their shapes in three dimensions (3D). The particles were identified by energy dispersive spectroscopy (EDS) in the SEM, and by X-ray diffraction (XRD) for bulk samples. Hot tensile testing (HTT) was conducted between 470 and 600uC to asses the hot ductility for each condition. The inferior ductility of as cast samples was due to the poor bond strength of the b AlFeSi phase at the grain boundaries. Homogenised samples, which contain a AlFeSi, exhibited improved ductility. Samples that were water quenched following homogenisation were absent of Mg 2 Si precipitates, when these elements remained in solid solution. These exhibited the highest ductility.

The Sequence of Intermetallics Formation during the Solidification of an Al-Mg-Si Alloy Containing La

“…This observation, although firmly supported by the EDS and XRD results, is in conflict with the fact that the b-AlFeSi is known to be the dominant Fe-bearing intermetallic in the direct chill (DC) cast 6xxx series alloys with a low Mn concentration. [5,27,28] This discrepancy can be explained if it is recalled that the cooling rates employed in this work were much lower than values typical of DC casting (~10 K/s). It seems that the formation of the b-AlFeSi phase is facilitated at high cooling rates.…”

Evolution of Fe Bearing Intermetallics During DC Casting and Homogenization of an Al-Mg-Si Al Alloy

“…[6] Therefore, a post-cast homogenization heat treatment is used commercially to encourage transformation of b to a to allow: (a) more reliable downstream deformation, typically by extrusion, (b) improved mechanical properties, especially toughness and elongation to failure, and (c) improved surface finish. [5,[10][11][12][13][14][15][16] Despite the apparent maturity of AA6xxx alloys, there is a significant on-going effort to optimize homogenization conditions in terms of properties, while also minimizing the homogenization time. Among the factors that govern the homogenization response, the initial cast microstructure and the alloy chemical composition play key roles.…”

Influence of quench rate and microstructure on bendability of AA6016 aluminum alloys

“…The a particles have a more globular morphology than the interconnected plate-like b particles, which are known to degrade the formability of these alloys by promoting the formation of voids during deformation [7,8,14,15]. The formability can thus be improved by promoting the formation of a particles instead of b particles when the alloy is homogenized; this can be accomplished by increasing the temperature and/or time of homogenization [10,14,15] or by adding a-stabilizer elements such as Mn [8,[15][16][17][18]. Regardless of particle type, alloys with a high content of Fe [2,3,5,[19][20][21] or Si [20,22,23] are generally recognized to have a poorer formability due to a higher quantity of intermetallic particles; however, we note that Davidkov et al [24]considered recently that large micron-size Mg 2 Si particles formed on grain boundaries are the critical parameter promoting fracture of alloy AA6016 during bending, rather than large AlFeSi intermetallic particles [24].…”

“…Depending on alloy composition, Mg 2 Si or Si particles about 100 nm wide can be found in 6xxx series aluminum alloys [8,11,12,18]. Their presence can be reduced with increased solution treatment time [25] or subsequent cooling rate [4,26].…”