Effect of alloying elements on the solidification characteristics and microstructure of Al- Si- Cu- Mg- Fe 380 alloy
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I.
INTRODUCTION
THE AI-Si-Cu ternary alloy system represents the greatest volume of aluminum alloys used by the diecasting industry. The most popular alloy in this system is the 380 alloy. 11'2'31 This combines the best of both AI-Cu and A1-Si binary alloys as copper alone does not render die-casting ability to aluminum, but in conjunction with silicon, enhances the strength of the diecastable A1-Si alloys. Other alloying elements present relatively in considerable amounts are zinc, iron, magnesium, and manganese. Chromium may also be present. Each of these elements confers a particular property: copper improves room and elevated temperature properties; tl,41 magnesium makes the alloy strong, hard, and responsive to heat treatment; tS-lz] iron gives strength and also prevents adhesion to steel dies (die soldering); t~-3'13] while manganese (depending on the amount) iron content, and cooling rate can prove to be beneficial or harmful. The impurities and the alloying elements partly go into solid solution in the matrix and partly form intermetallic compounds during the solidification of the metal. The properties of the 380 alloys are determined by the fineness of the microstructure and the distribution of the phases. Two major factors which affect these are the alloy solidification rate and the alloy composition. Alloy solidification rate controls the fineness of the structure and is governed by the casting process used, i . e . , sand, permanent mold, die casting, etc. The form and distribution of the phases is controlled by the concentration of the main alloying elements and impurities present. Composition variation within the specification can have a significant effect on the microstrncture and, hence, the properties. Also, the solidification sequence is influenced to a considerable extent by the interaction of the alloying elements like iron, silicon, manganese, copper, zinc, and magnesium. S. GOWRI, Research Associate, and F.H. SAMUEL, Research Professor, are with the Department of Applied Sciences, University of Quebec at Chicoutimi, Chicoutimi, PQ, Canada. Manuscript received April 21, 1993.
METALLURGICAL AND MATERIALS TRANSACTIONS A
The presence of a high amount of alloying elements in 380 alloys complicates the solidification process, and there is a need to understand the role of each element and how it affects the properties and the interrelationship between these elements to achieve optimum properties. The purpose of this study is to evaluate the effect of varying the major alloying elements within the specification limit and solidification rate on the solidification behavior, microstructure, and distribution of phases in 380 alloys. The alloying elements investigated are copper, zinc, magnesium, manganese, and iron, and the cooling rates are 0.4 and 10 ~ Studies of this nature are not available in literature. The only published work of this type to the authors' knowledge is that of Backerud et al. [14] They studied the solidification behavior of about twelve 380-type alloys, collected from various sou
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