A little word about aluminum skid plates vs. steel skid plates courtesy of skidplates.com:
Q: Why not make skid plates from lighter weight aluminum?
A:If you're building a competition vehicle where every pound counts, aluminum makes sense. Unfortunately, aluminum tends to gouge more easily than steel, and from our experience doesn't hold up as well in the long run. Quite of few of our customers have replaced their aluminum skid plates with steel ones because the aluminum skids didn't last. Why not buy steel skids to begin with?
Taken from here: http://www.skidplates.com/SkidPlatesQA.asp
Q: Why not make skid plates from lighter weight aluminum?
A:If you're building a competition vehicle where every pound counts, aluminum makes sense. Unfortunately, aluminum tends to gouge more easily than steel, and from our experience doesn't hold up as well in the long run. Quite of few of our customers have replaced their aluminum skid plates with steel ones because the aluminum skids didn't last. Why not buy steel skids to begin with?
Taken from here: http://www.skidplates.com/SkidPlatesQA.asp