Solute micro-segregation profile and associated precipitation in cast Al-Mg-Si alloy

The micro-segregation in as-cast AA6082 aluminum alloy were investigated across length scales using a combination of analytical electron microscopes. It is found that the micro-segregation bands form an inter-connected network following grain boundaries and inter-dendritic channels. The micro-segregation can be divided into major micro-segregation and minor micro-segregation; the
former is mainly on the grain boundaries consisting of Fe-bearing intermetallic; the later occurs both, along the grain boundaries and inter-dendritic channels, consisting mainly of Mg and Si alloying elements. The atomic-scale imaging reveals that in the minor-segregation bands, the increased supersaturated solute concertation has formed precipitates that had either nucleated heterogeneously on the dislocation network or homogeneously inside the aluminum matrix. The heterogeneously nucleated precipitates in the dislocation lines are composed of a mixture of phases down the precipitation sequence meanwhile, the homogenously grown ones are discrete phases that appear at the early stages of the precipitation sequence.