good work sunny :_)
cast steel is better than cast iron, and steel better than alu.
just for general fyi (though there are other factors!)
Steel generally has yield strengths ranging from 30,000 - 150,000 psi, and ultimate strengths ranging from 50,000 - 200,000 psi.
Aluminum generally has yield strengths ranging from 15,000 - 70,000 psi, and ultimate strengths ranging from 30,000 - 90,000 psi.
So, there is some overlap, but in general, steel is stronger.
Aluminum in general is a third as light and half as strong as steel, or the inverse, steel is twice as strong but three times as heavy. It is also softer and more prone to fail over less deflection.