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I have been researching on how to form AZ91 Common Magnesium Alloy which consists of 90% Mg, 9% Al, 1% Zn, 0.3% Mn. Referring to the article at here, I have read and highlighted important text and trying to picture it in the Mg_Al Phase Diagram, but it looks very weird because the final composition should consist of 90% Mg which is in hyper-eutecoid region which is not mentioned in the text. Can anyone show a formation of AZ91 Magnesium Alloy using the Mg-Al phase diagram as shown?

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  • $\begingroup$ In the real world it will likely be solution annealed and age hardened . Rapidly cooled from 415 to give a relatively uniform material , then aged. $\endgroup$ Commented Nov 4, 2022 at 0:42

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The explaining text is horrible.

The hypo/hyper refers to the amount of Al in the Mg relative to the eutectic point, so mentally flip the diagram if you want. "Hypo" is compositions to the right of the eutectic, "hyper" to the left.

The solidification discussed is starting up near the Mg melt point at nearly pure Mg composition, and coming down the solidus until the eutectic temperature is reached (but way over at the pointy bit on the Mg phase). This leads to the increasing percentage of Al in the solid with time. At that point, any remaining liquid solidifies into (Mg) + ($\gamma$-Mg$_{17}$Al$_{12}$). Until that point, all the solidified material has an Al composition below that of the eutectic. Only the Mg$_{17}$Al$_{12}$ exceeds the eutectic composition.

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