Mahle Gmbh

Heinz Wimmer

Karlheinz Bing

Martin Ruhle

Detlef Schlosser

Fritz Warth

Rudiger Herrmann

Piston with cooling channel

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.

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Leonberg, Germany

Heinz Wimmer