Potassium, calcium, sodium, magnesium, aluminum, zinc, iron, tin, lead, copper, mercury, silver, platinum, gold, this is order sheet metal activities, from here you can find gold properties of aluminum than zinc is strong, so the same material in the galvanic cell anode, aluminum, zinc do when the cathode, lose the ability of electrons to be stronger than zinc aluminum, which means reducing is stronger than zinc aluminum, In fact, in industry or life to protect the metal is generally iron, and both can play a protective role, to say the difference, it seems not big