Modification of Outer Layer of Al-Si Alloys by Doped Fe Atoms

Abstract

The modification of the outer layer of Al-Si alloys doped with iron atoms was examined. The samples both were taken from automotive pistons and they also were prepared in the laboratory. In any case, they were used as basic raw materials for examination. It was found that the structure and properties of these alloys are very much dependent on the cooling rate, composition and heat treatment. The iron atoms are usually doped, in order to diminish and stabilize the thermal expansion coefficient of the alloys. However, this process makes the alloys to become harder and harder; thus leading the alloys to a degradation of their mechanical behavior at elevated temperatures. Optical Microscope observations, SEM analysis of the interactive surface layers and XRD measurements were performed on tested samples. At elevated temperatures a large homogenized zone extended to about 500 (μm) without an apparent distribution of the silicon dendrites or faceted crystals was formed. Moreover at the surface of the so called homogenized zone a layer of about 35 (μm) was formed inside of which iron atoms were migrated. This layer is mainly responsible for scuffing phenomena.