Metals combine with oxygen to form metal oxides. For example iron wool burning in oxygen produces iron oxide
The chemical equation.
Iron + Oxygen –> Iron oxide
Aluminium + Oxygen –> Aluminium oxide
Aluminium is reactive enough to chemically combine with oxygen atoms that are already attached to another metal atom.
Aluminium + Iron oxide –> Aluminium oxide + iron
This is known as a thermite reaction . A huge amount of heat is given out and the iron formed is molten. The reaction has been used by NZ rail to weld continuous sections of line together.