although thermodynamicaliy feasible in practice, magnesium metal is not used for the reduction of alumina in the metallurgy of aluminium. why?

Thanks alby Abraham

it is also because  Mg is a costly metal so it is not economically feasible.

Temperatures above the point of intersection of Al2O3 and MgO curves, In the Ellingham diagram, magnesium can reduce alumina. But the temperature required would be so high that the process will be on economic and technologically difficult

Magnesium can reduce alumina below the temperature of nearly 1350° C.But the process will be uneconomical or non profitable as: If you compare the magnesium price (about 2$ per pound) to the aluminum price (about $0.80 per pound) you can see it is unprofitable. Even considering the elements' relative atomic weight, you would still be losing money if you did that. Source:Chemistrystackexchange

If you compare the magnesium price (about 2$ per pound)  to the aluminum price (about $0.80 per pound)  you can see it is unprofitable.

Even considering the elements' relative atomic weight, you would still be losing money if you did that and metallurgy is all about business and profit, thus Mg metal is not used for the reduction of Alumina in the metallurgy of Aluminium

In the Ellingham diagram, Al2O3 and MgO curves intersect to A point at the temperature below 1623K . Hence, Mg can reduce alumina but Mg is a vostlier