High resolution transmission electron microscope observation of the metastable phase in an aged commercial AA6063

We have investigated the morphology of AlFeSi intermetallic compounds and the effect of Fe on the crystal structure of the metastable phase in a commercial 6063 alloy by transmission electron microscope(TEM). As the result, we could recognize a monoclinic structure β-AlFeSi and a hexagonal structure α'-AlFeSi in a commercial 6063 alloy. And there were many precipitates that the bright dots in the cross sections array irregular and parallelogram until the hardness achieves to a maximum value. At a later stage of aging, lots of them array hexagonal. Moreover, the number of precipitates per unit area has a relationship with hardness up to peak hardness.