The structures expected in a simple ternary eutectic system: Part II. The Al-Ag-Cu ternary system

Abstract

Ternary alloys of various compositions from the aluminum rich corner of the Al-Ag-Cu system were directionally solidified at several different growth rates ranging from 6.4 × 10⁻¹ mm·S⁻¹ to 5.6 × 10⁻³ mm· s⁻¹. The region of two phase coupled growth between α-Al and CuAl₂ was determined at a growth rate of 6.4 × 10⁻¹ mm· s⁻¹. The composition range over which a fully ternary eutectic structure formed was investigated for several different growth rates. The results are found to be consistent with the predictions of the competitive growth model set out in Part I,¹ and it would seem that the ternary eutectic composition of the published phase diagram may be incorrect. Scanning electron microscopy, using the backscattered electron signal, was used, together with optical microscopy, to study the microstructures formed. The ternary eutectic between α-Al, Ag₂Al, and CuAl₂ was found to be semiregular, and the unusual morphology of the two phase dendrites between α-Al and Ag₂Al is explained.