Abstract: The aim is to improve the strength of an intermetallic bond between engine component made from an aluminium alloy and a reinforcing element made from austenitic cast iron. For that purpose, the reinforcing element is annealed in a decarbonising atmosphere before the known prior art alfin process is carried out, in order to obtain an alfin layer largely free of graphite scales.

Abstract: In a reinforcing component made from austenitic iron which is bonded intermetallically with an engine component made from an aluminium-base alloy, in particular a piston, the aim is to improve the strength of the bond irrespective of the graphite configuration in the base material. For that purpose, the structure at least on areas of the reinforcing component surface in the vicinity of the intermetallic bond is austenitic-ledeburitic.

Abstract: For a piston consisting of an Al-Si alloy having a mean linear grain diameter of the Silicon eutectic of more than 3 .mu.m for combustion engines and provided with a hard-oxidized top, the structure of the base material to be oxidized is subjected to a grain refinement in the depth to be oxidized so that the silicon eutectic has a mean linear grain diameter of less than 3 .mu.m, preferably less than 2.5 .mu.m. By this means, the resistance to erosion of the hard-oxide layer is improved. The grain refinement may be effected in the respective zones during the casting of the piston or thereafter by re-melting those zones prior to oxidizing. If the risk of erosion exists only in specific locally limited zones of a relatively large hard-oxide surface, then a grain refinement confined to these zones is sufficient.