Well ridgid wrenches are all cast (either iron, or in this case aluminum), if that helps any.
I've never seen a pipe wrench handle machined from billet, but the ampco pipe wrenches I have, have a machined head (the ell part at the top, not just the jaws), where every other one I've seen has that part made from cast iron (even when the handle is aluminum).
BUT, if the wrench is actually a RIDGID brand, you might want to know that its covered by a lifetime warranty.
Have a look at:
http://www.ridgid.com/Tools/RIDGID-Warranty/index.htmHand tools (pipe wrenches etc.) should be returned to the place of purchase.
BTW, if your local supplier won't take it back, try a Home Depot. They're pretty good at warranty replacements.
-- Robert