The characterization of the A1-12 Wt Pct Si flake powder produced by a double-disk process
- PDF / 1,428,226 Bytes
- 11 Pages / 613 x 788.28 pts Page_size
- 28 Downloads / 150 Views
I.
INTRODUCTION
ALUMINUM flakes with a thickness of about 0.1 to 3.0 /xm are typically converted from the gas-atomized powder by a ball-milling process. They have found applications as pigment in industrial paints, roof coatings, paper coatings, and printing inks) ~1A new kind of aluminum flakes with dimensions one to two orders larger than conventional flakes has been developed during the past 2 decades, as produced directly from the melt by rapid solidification techniques. These techniques can be divided into two categories. One category involves atomizing the melt into fine droplets by an external force and then allowing them to come into contact with a solid substrate. Each droplet subsequently spreads into a liquid film and solidifies as a flake. For example, ALCOA* *ALCOA is a trademark of the Aluminum Company of America, Pittsburgh, PA.
Splat processt2~ allows air-atomized droplets to spray onto a water-cooled rotating drum, thereby producing aluminum flakes with a pancake shape. The method developed by Jones and Burden ~31 permits centrifugally atomized droplets to come into contact with the chamber wall and produce pancake-shaped flakes. The other category entails causing the melt to come into contact with the serrated surface of a rotating drum and form flakes on serrations. Melt spinning and melt extraction14j are two typical examples of methods for producing aluminum flakes. The aluminum flakes, as formed under a KUANG-YUAN SHUE, Graduate Student, and JIEN-WEI YEH, Professor, are with the Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China. Manuscript submitted December 17, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS A
cooling rate of 105 to 106 K/s, have a much finer ascast microstructure than that obtained by the conventional ingot casting method. A typical application of these aluminum flakes is as a starting material to be consolidated to form structural materials by powder metallurgy process. The materials thereby produced often have superior properties to those produced by ingot metallurgy, tsj Besides, a highly promising application in EMI shielding materials has already been developed, tr~ The aluminum flakes are added into polymers to produce composite materials. When the addition exceeds a critical concentration, the flakes interconnect with each other to form a conductive network and permit the composites to be conductive and have an electromagnetic shielding capability. Aluminum flakes have been verified to be the most economically feasible type in making conducting composites among the many varieties of conductive fillers, e.g., carbon black, stainless fiber, and metallized glass fiber.trl An electromagnetic shielding capability of 50 dB has been achieved by incorporating 40 wt pct of Transmet's aluminum flakes (with an aspect ratio of 40) into a plastic matrix. However, a demand still persists in reducing the critical concentration of aluminum flakes. The reduction will lessen the fabrication difficulty and the mechanica
Data Loading...
