PURPOSE: To improve the durability of a material having upgraded high- temperature corrosion resistance by taking advantage of the formation of an intermetallic compound such as Ni3Al to clad the material with Al2O3.

CONSTITUTION: A clad metal is obtained by cladding at least one face of a base metal 1 with an Al sheet 3 and a Ni (or Nb) sheet 2A in a manner that the latter sheet lies between the first two. The clad metal is annealed in a vacuum and then heated in an oxidizing atmosphere to form one intermetallic compound layer of Ni3Al (or Nb3Al) 4 and/or another of NiAl (or NbAl) 5 between the Al layer 3B and the Ni (or Nb) layer 2B and simultaneously an Al2O3 layer 6 on the surface. All the intermetallic compounds such as Ni3Al, NiAl, Nb3Al and the like are superior in heat resistance and corrosion resistance, capable of protecting the underlying base metal without permitting the underlying base metal to be corroded even if there occur miniscule cracks on the Al2O3 layer cladding the surface.