Aluminum super alloys (Like 7075 and 6061) exceed mild steel tensile strengths once precipitate hardened (heat accelerated aging) but even in it's softer forms can function quite adequately in these applications. All it takes is a thicker casting to achieve similar stiffness.
In theory the wear and friction coefficient might be a hurdle, but in the real world most folk are *never* gonna wear out a bore- especially if lubing occasionally.
So I'm generally in the same boat as Jmorris. Aluminum is a good choice to drop cost since it's very easy to cast, and cast cheaply. As long as it is properly designed to accommodate any differences in yield (not tensile) strength. Would I prefer a drop forged alloy steel press? Well, yeah. But I'd also like to have titanium wheels on my ride. The question is what will I *pay* for them!
