Morphology and Phase Formation During the Solidification of Al-Cu-Si and Al-Ag-Cu Ternary Eutectic Systems

Carina Morando,Osvaldo Fornaro

doi:10.1590/1980-5373-mr-2017-0930

Abstract

The microstructure of ternary alloys in the Al rich corner of the Al-Cu-Si and Al-Ag-Cu systems were analyzed in order to determine the solidification path in the different structural regions expected from the equilibrium phase diagram. The analysis was based on theoretical models developed in the literature for solidification of ternary eutectic system alloys under simple lever rule assumptions. Optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDAX) were used to study the microstructure formed in each case. The observations were consistent with model predictions: Al-Cu-Si system showed two binary eutectics: non faceted-non faceted (nf-nf) AlCu and faceted-non faceted (f-nf) AlSi, Al-Ag-Cu system showed 2 binary regular eutectics (nf-nf) and a ternary semi-regular Brick type eutectic. The results provided an example of a methodology for use in ternary and multicomponent alloys.

Highlights

Primary manufacturing processes such as ingot casting, continuous casting, squeeze and pressure casting and secondary manufacturing processes such as welding and soldering, involve solidification as an important stage of the process[1]
The alloys selected for the present work were chosen as representative examples of different structural regions as predicted in the work of McCartney et al.[5,6] for a simple hypothetic ternary eutectic system taking into account the solidification path according to the equilibrium diagram
The richer liquid falls close to the ternary eutectic composition, and the solidification ends in the coupled zone, where a binary reaction could be absent

Summary

Introduction

Primary manufacturing processes such as ingot casting, continuous casting, squeeze and pressure casting and secondary manufacturing processes such as welding and soldering, involve solidification as an important stage of the process[1]. Many commercial materials are multicomponent alloys, whose mechanical or functional properties are determined by the microstructure that develops during the solidification and subsequent processing stages. One of the essential challenges to materials science is to understand how solidification microstructures form and how they can be controlled by selecting the alloy composition and processing parameters. Fundamental knowledge on solidification has been developed mainly for pure materials and for binary alloys exhibiting single phase growth (solid solution) and/or two phase growth in eutectic and peritectic class reactions[3]. The classical analytical description for steady-state eutectic growth in binary alloys, developed by Jackson and Hunt[3], describes the relationship among the undercooling ∆T in front of the isothermal interface, the growth velocity V and the lamellar spacing λ in the case of regular (i.e non faceted-non faceted) growth at low velocity for phases with similar densities: DT

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