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Metallurgical and Materials Transactions B-Process Metallurgy and Materials Processing Science


Die soldering is the result when molten aluminum sticks to the surface of the die material and remains there after the ejection of the part; it results in considerable economic and production losses in the casting industry, and is a major quality detractor. In order to alleviate or mitigate die soldering, one must have a thorough understanding of the mechanism by which the aluminum sticks to the die material. A key question is whether the die soldering reaction is diffusion controlled or interface controlled. A set of diffusion couple experiments between molten aluminum alloy and the ferrous die was carried out. The results of the diffusion couple experiments showed that soldering is a diffusional process. When aluminum comes in contact with the ferrous die material, the iron and the aluminum atoms diffuse into each other resulting in the formation of a series of intermetallic phases over the die material. Initially iron and aluminum react with each other to form binary iron-aluminum intermetallic phases. Subsequently, these phases react with the molten aluminum to further form ternary iron-aluminum-silicon intermetallic phases. Iron and aluminum have a great affinity for each other and the root cause of die soldering is the high reaction kinetics, which exists between iron and aluminum. Once the initial binary and ternary intermetallic phase layers are formed over the die material, the aluminum sticks to the die due to the abnormally low thermal conductivity of the intermetallic phases, and due to favorable interface energies between the intermetallic layers and aluminum. The experimental details, the results of the interface reactions, and the analysis leading to the establishment of the mechanism giving rise to die soldering are reviewed discussed.





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Copyright 2002, ASM International. This paper was published in Metallurgical and Materials Transactions B-Process Metallurgy and Materials Processing Science Vol. 33 Iss. 3 pp. 465-476 and is made available as an electronic reprint with the permission of, ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.