Does the subject want to ask "which metal materials must be released through nickel"? Iron, zinc.

1. Iron: Iron can react with nickel, and iron atoms can replace nickel atoms in nickel alloys, so that nickel elements can be released from nickel alloys.

2. Zinc: The standard electrode potential of zinc is more negative than that of nickel. Zinc can make nickel in nickel alloy gain electrons and be released, which belongs to the spontaneous release of nickel caused by the strong reduction of zinc.