Rapid Solidification of an Aluminum-Neodymium Alloy
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RAPID SOLIDIFICATION OF AN ALUMINUM-NEODYMIUM ALLOY
S. J. SAVAGE AND F. H. FROES Materials Laboratories, Aeronautical Force Wright Air Structural Metals Branch, Wright-Patterson AFB, OH 45433
Laboratory,
ABSTRACT A rationale for rapid solidification processing of aluminum-lanthanide alloys is given, and preliminary results of microstructural studies on an aluminum-neodymium alloy Three distinct types of microstructure are are presented. seen in the as-cast rapidly solidified material, which are still evident after heat treatment at 350*C for 1 hour. Microhardness measurements indicate each microstructure has a different response to isochronal heat treatments.
INTRODUCTION in recent The development of rapid solidification processing (RSP) value for years has allowed alloy systems previously thought to be of little Because of their low solubility structural materials to be reexamined [1]. the lanthanides in aluminum fall in this category. The equilibrium phase diagram [2] for the aluminum-neodymium system typical for all the aluminum-lanthanide systems, (Figure 1), which is different from the melting point of indicates a eutectic at 637°C; little pure aluminum. Beyond the eutectic composition, the temperature of the liquidus line does not increase rapidly. At the eutectic temperature, the liquid solubility of neodymium is high, about 30 wt %. The solid solubility at the eutectic temperature is low, about 0.04 wt %, and decreases to The equilibrium intermetallic negligible levels (0.005 wt %) at 500*C. compound formed, assumed to be Nd 3 A11 1 , contains a high proportion of aluminum. Relative to a conventionally cast material, RSP can generate highly in which gross intermetallic particles are refined microstructures For such a eliminated and finely dispersed phases may be formed [1]. microstructure to be useful it should also be stable, and the properties of the dispersion such as to enhance the mechanical properties of the matrix. To date, little is known of the aluminum-lanthanide intermetallic compounds, although they are in general hard phases, Nd 3 A1 1 1 , having a Vickers hardness of 3,500MPa [3]. The diffusion coefficients of the lanthanides in aluminum appear to be considerably lower than for solutes, such as the transition metals manganese and iron which are known to live stable dispersions in 7 0 cm s-1 in the range 450-630 C aluminum [4]. For neodymium, D = 4.8 x 10[5]. The other major factor influencing stability is solubility, and as discussed above, this is low -- again favorable for a stable dispersion. an investigation of the On the basis of these characteristics aluminum-lanthanide systems by RSP is in progress [6]. Preliminary results of this work, on an aluminum-neodymium alloy will be presented in this paper.
Mat. Res. Soc.
Symp.
Proc. Vol.
28 (1984)
Published by Elsevier Science Publishing Co.,
Inc.
330
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