To form a hardened build-up layer having large peeling resistance and practically sufficient thickness of the surface by integrally forming the hardened friction build-up layer on the thermal-sprayed layer on the surface of an aluminum product.

For example, a rod material 3 of ferrous hardened metal, etc., is pressure-welded to the thermal-sprayed layer 2 on the aluminum product 1 and friction heat in generated by rotating the rod material and the build-up layer 4 is obtd. to the necessary position while moving this rod material 3. Pressing force applied to the rod material 3 at this time, this rotating speed and further, moving speed are properly selected under consideration of the hard metal as the rod material 3, the composition of the thermal-spraying layer 2 and the necessary thickness of the build-up layer 4, etc., Further, as for the build-up layer, the necessary position of formed beforehand as e.g. the part of difference in level, and also the build-up position is formed as the flat surface as the whole surface of the aluminum product 1. In such a way, the surface condition after build-up can be made various.