Homogenization of direct dill cast AlSi1MgMn billets

The homogenization practice for direct chill cast AlSi1MgMn billets was investigated. It takes 8 h at 570 degrees C and at least 4 h at 580 degrees C to even out the Mg and Si distribution in the aluminium matrix and to obtain relatively small discrete alpha(c)-Al-12(Fe,Mn)(3)Si particles with a "necklace" configuration. Once Mg and Si are solutionized, the equilibrium beta-Mg2Si phase precipitates during post-soaking cooling at >= 500 K h(-1) beta'-Mg2Si precipitates are also identified in samples cooled at <= 250 K h(-1). Hardness produced in this cooling rate range is relatively lower suggesting improved extrudability. These billet samples are fully solutionized at 500 degrees C during billet pre-heating. Typical press exit temperatures may suffice for adequate age hardening in billet samples soaked at 580 degrees C for 8 h and subsequently cooled at 250 K h(-1). This is a very attractive feature as it implies a full age hardening capacity even without the need for a separate solution heat treatment.