The squeeze casting of hypoeutectic binary Al-Cu
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I.
INTRODUCTION
SQUEEZE casting is a method of producing near-netshape components. Unlike high-pressure die casting where the melt enters the casting chamber at a high velocity, greater than 10 ms21, squeeze casting uses a much slower rate of injection, typically less than 0.5 ms21. At this low rate of mold filling, the casting is less inclined to experience turbulent flow and associated surface breakup and casting defects.[1] There are two methods of squeeze casting, horizontal and vertical, depending on the direction that the pressurizing ram directs the melt charge or shot into the die cavity. Horizontal squeeze casting shares much in common with pressure die casting, where a metered shot is thrust into the die via a horizontally acting ram (Figure 1). In squeeze casting, however, the shot speed is low and the internal soundness of the casting is greatly improved, thus allowing postsolidification heat treatments. There are two types of vertical squeeze casting, direct and indirect. Indirect vertical squeeze casting uses a ram to push the melt upward into the die chamber (Figure 2), where the melt speed and even the rate of feeding may be controlled by varying the ram velocity. Alternatively, direct vertical squeeze casting uses a ram and an open-faced die assembly (Figure 3). In this case, a metered amount of metal is poured into the die and a downward acting ram impacts upon it. Commercially, direct squeeze casting predominates.[2] It is common for the squeeze-casting pressure to be continuously applied until it reaches a limiting upper value, usually in the order of 100 MPa. At this level of pressurization, a variety of useful effects are produced. The applied pressure increases the heat-transfer coefficient between the die and the casting,[3] and this leads to comparatively short M. GALLERNEAULT, formerly Nato Research Fellow with the Oxford Centre for Advanced Materials and Composites, Department of Materials, Oxford University, is Senior Scientist with Alcan International Ltd., Kingston, K7L 5L9, ON, Canada. G. DURRANT, Research Fellow, and B. CANTOR, Head of the Department of Materials, are with the Oxford Centre for Advanced Materials and Composites, Department of Materials, Oxford University, Oxford OX1 3PH, United Kingdom. Manuscript submitted February 14, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS A
solidification times, high cooling rates, and fine-scale microstructures. In addition, the applied pressure is high enough that alloys that are not usually considered shape castable, such as those with long freezing ranges, high viscosities, and large surface tensions, may be successfully cast.[4,5] The process can be easily modified for the infiltration of fiber preforms for the production of locally reinforced metal matrix composites.[6,7] Provided the die cavity and feeding system are correctly designed, the applied pressure is large enough to feed shrinkage porosity fully and to reduce or eliminate the development of gas porosity.[8] Hence, squeeze-cast parts tend to have very low levels of poros
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