Composition: Al-6.7%Si-0.37%Mg-0.15%Fe-0.15%Ti.

Processing: Semisolid casting (Rheocasting).

Etching: 10-15s immersion in 0.5% HF.

The micrograph shows a globular structure of the primary α-Al phase. This is the result of semisolid processing where stirring breaks up the dendrites when they are still surrounded by liquid. This refined microstructure shows that the α-Al+Si eutectic in between the globules has a fibrous or modified morphology. At high magnification, two intermetallics are visible: β-AlFeSi (needles/plates) and π-AlFeSiMg (chinese-script). When compared with the A361 alloy it is evident that semisolid processing transforms the primary phase and refines the eutectic, which results in improved mechanical properties.

Al-Si diagram

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