There was a thread done on this already. Try the search. Nothing might come up (the seach is erratic sometimes) but if anyone finds the link, post it and I'll be happy to merge them.
But no, he doesn't have iron, he's all plastic, but he's not the best attacker and would have a hard time hurting Mags.
Magneto could encase him in a force field and shoot him into orbit.
Magnetos force fields can contain plastic man despite there being no metal in his form. His forcefields can contain and shunt away non metallic objects . (As shown in X-men the time Zaladane had absorbed Magnetos powers and there was an avalanche in her base)