They are probably aluminum and are not dishwasher safe. Found that out this morning when I went to make cookies after putting my beater in the dishwasher. It oxidized and turned gray with a black residue. I've had my KitchenAid for years since my children were babies. They are in in their thirties. Very upset  this replacement didn't hold up to KA reputation. I got my children KA for wedding gifts....need to warn them of this problem. Shame on you KA!