Aluminum also has high electronegativity. As the detail shows, there is clearly a ferrous hinge pin holding the two halves of the aluminum casting together, ensuring the kind of galvanic couple that ensures that between citrus juices and high pH-level detergents, you are going to see all sorts of exotic reactions. Geez, it's a fricking battery! While the baked enamel coating on this part was clearly intended to protect against exactly this type of thing and is harder and more wear resistant than paints, it clearly failed in its duties. Designers probably chose it because it's cheaper (it's often a one-coat process) and more decorative than paint, though, which clearly were the wrong performance trade-offs in this application! Stainless steel or some sort of filled polymer seems like it would be a better choice, or clear instructions on NOT running the part through your dishwasher.