Effect of Modification of Rare Earth Elements on the Morphology of Silicon Precipitates in the ZnAl40Cu3Si Alloy

Abstract

Properties of the alloys Zn-Al-Cu can be improved by partial or total replacement of copper with silicon. The previous studies of the current authors have shown that in alloys with silicon addition its precipitates are not evenly distributed. This can lead to uneven wear of parts made of the Zn-Al-Cu alloy. The study of phenomena occurring during the crystallization of the ZnAl40Cu3Si alloy with ATD methods have shown that silicon does not form compounds and solid solutions with Zn and Al. In the examined alloy silicon is released as the primary even before the actual solidification of dendrites. It is not possible to reduce the uneven distribution of precipitates through heat treatment. Therefore it is important to assure the uniform distribution of precipitates of silicon already on the crystallization stage, e.g. by addition of rare earth elements. The purpose of this study was to determine the effect of rare earth elements on the morphology of silicon precipitates in the ZnAl40Cu3Si alloy. The investigated material were alloys containing 40 wt% Al, 3 wt% Cu and 1.5 wt% Si (Zn - remaining). The samples have been taken from the top, middle and bottom of the ingot. In order to determine the morphological characteristics of silicon precipitates a computer program Met-Ilo developed in the Department of Materials Science, Silesian University of Technology was used. Changes of the volume fraction and shape of precipitates in particular areas of the ingot were the subject of analysis in this work.