Abstract
The homogenization practice for direct chill cast AlSi1MgMn billets was investigated. It takes 8 h at 570 °C and at least 4 h at 580 °C to even out the Mg and Si distribution in the aluminium matrix and to obtain relatively small discrete αc-Al12(Fe, Mn)3Si particles with a “necklace” configuration. Once Mg and Si are solutionized, the equilibrium β-Mg2Si phase precipitates during post-soaking cooling at ≥ 500 K h–1. β′-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 °C during billet pre-heating. Typical press exit temperatures may suffice for adequate age hardening in billet samples soaked at 580 °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.
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