The microstructures and properties of an al- 12 wt pct
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I.
INTRODUCTION
RAPID solidification is well known for having the merits of grain refinement, extension of solid solubility, and reduction of segregation and particle size. In exploiting these merits to promote the properties of materials, the powder metallurgy (PM) process is usually considered as a typical route in which the melt is first disintegrated into fine particles, filaments, or ribbons and then consolidated as a form of bulk materials. 1~-Sj However, due to many extra steps required in this process and the high surface/volume ratio involved, it is difficult to avoid serious contamination and oxidation. This, in turn, creates a big problem for achieving high-quality PM alloys, t~l In view of the above disadvantages, many efforts have been exerted on developing a new rapid solidification technique for producing bulk materials directly. The spray deposition method t6'7'8~ and vacuum evaporation method t9,~~ are typical examples. The former method is the impinging of liquid jets or molten drops on a substrate and obtains a deposit of bulk material. It can reach a cooling rate of 103 K / s and yield a lower oxygen content than PM. The mechanical properties were also reported to be better than the PM process. The latter method heats the molten alloy in vacuum and lets the vapor deposit upon a substrate to build up a bulk material. It can produce aluminum alloys with large supersaturation, fine constituents, and subsequently attractive mechanical properties. In the present work, a new rapid solidification process for directly producing bulk materials was developed based on the hammer-and-anvil concept, tIll In this method, a melt-supply system and hammer-quench system were designed to operate in cyclic mode, so that bulk material in the form of slab can be created layer by layer. In consideration of the nice fluidity, weldability, and dispersion hardening potential, AI-12 wt pct Si alloy was chosen JIEN-WEI YEH, Associate Professor, and CHUN-HUEI TSAU, Graduate Student, are with the Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China. Manuscript submitted January 5, 1990. METALLURGICAL TRANSACTIONS A
as the experimental material. For evaluating the new process, microstructures and mechanical properties were investigated in comparison with those of conventional ingot process. II.
EXPERIMENTAL PROCEDURE
A. The Layer-Deposition Process The experimental equipment developed for producing layer-deposited bulk alloys is shown in Figure 1. It consists of a hammer-quench system and melt-supply system. The hammer-quench system has three parts, a refractory anvil, a water-cooled copper hammer 150 mm in diameter, and an air cylinder. The copper hammer is connected with the cylinder and is able to reciprocate motion against the anvil. The melt-supply system is a zirconia-coated stainless steel crucible with a flowpipe in the bottom. In order to control the amount of melt injecting on the anvil in each cycle, a stopper was designed to be adjustable in stroke
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