Simple switch has two pieces called "contact" metal, second contact current loops, two contacts do not touch current when open. Should be considered when selecting contact metal against corrosion degree as most metal oxidises to form insulating oxides, contact does not work. Select the contact metal would also need to consider the electrical conductivity, hardness, mechanical strength, low cost and toxicity, and other factors.
Sometimes at the contact corrosion resistance of electroplated metal. General plating in contact contact surface in order to avoid affecting its performance because of the oxide. Sometimes interface will use non-metallic conductive materials such as conductive plastic.