Crystallization studies in the aluminum-rich corner of the aluminum-iron-manganese system
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I.
INTRODUCTION
A S noted by Phillips ~the eutectic trough between the fields of primary aluminum and (FeMn)AI6 crystallization "sets a limit to the amount of iron that can be tolerated in commercial aluminum-manganese alloys." This observation has even more relevance today since the steadily increasing recycle of scrap aluminum may be expected to cause higher manganese and iron levels by selective oxidation of aluminum during melting. Because preliminary crystallization studies using recycle can scrap aluminum containing low magnesium and silicon contents indicated that the eutectic trough involving (FeMn)A16 and aluminum crystals may be much closer to the composition of pure aluminum than reported by Phillips, it was decided to reinvestigate the aluminum-rich region of the A1-Fe-Mn system. Although Phillips ~ had used thermal analyses with 200 g samples and separate quenching experiments, the authors combined these two methods using a single apparatus. Mehrabian and Flemings 2 showed that vigorous agitation led to the growth of relatively large and rounded crystals of aluminum from an alloy containing 8.5 pct Si, 3.5 pct Cu, and 1 pct Fe. It was therefore decided to use a relatively large bath of the aluminum alloy concerned, to produce crystals by cooling while stirring, and to obtain samples of the slurry by sucking approximately 1 g of the slurry into a silica tube and quenching in water. Preliminary experiments confirmed the growth of large rounded aluminum crystals and also showed that the polygonal intermetallic crystals ((FeMn)A16 and FeAI3) grew to a relatively large size. The large size of the primary crystals compared to the fine dendrites formed as a result of rapidly quenching these small samples enabled the identity of the crystals formed at temperature to be preserved during quenching. The nature of the primary crystals formed by crystallizing an alloy of known composition was determined by metallographic examination and/or electron probe analysis of a series of quenched samples taken throughout the course of each experiment. Timetemperature records were also made for each run to provide guidance in the selection of samples for examination.
W.T. DENHOLM, Section Leader, J.D. ESDAILE, Senior Principal Research Scientist, and N.G. SIVIOUR and BRUCE WARD WILSON, Experimental Officers, are all with the CSIRO Division of Mineral Engineering, P, O. Box 312, Clayton, Victoria, 3168, Australia. Manuscript submitted June 28, 1983. METALLURGICALTRANSACTIONS A
The phase diagram resulting from the present work is illustrated in Figure 1. This shows the two eutectic troughs represented by the lines originating from the eutectic point V of the A1-Mn system and from the eutectic point T of the A1-Fe system, and these lines terminate at the ternary eutectic point S. The line TS representing the upper eutectic trough separates the areas of primary crystallization of FeAI3 and AI, and the lower line SV separates the areas of primary crystallization of AI and (FeMn)AIo.
II.
EXPERIMENTAL
The apparatus used for t
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