PRODUCTION OF Ag-(Bi, Pb, Tl) -Al ALLOYS' FIBER AND CONTROL OF THEIR SOLIDIFICATION STRUCTURES

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The control of the solidification structure of a metal alloy that is closely connected with the mechanical property is very important. For alloys with very wide solidification temperature range above 550K such as Silver-Bismuth (Ag-Bi), Silver-Lead (Ag-Pb) and Silver-thallium (Ag-Tl) binary alloys, also the development of continuous fiber production by the In-Rotating-Water-Spinning process is very expected. Because the equilibrium phase diagrams of these three alloys show striking similarities, the standardization of the relation between the solidification microstructure and the cooling rate was tried. Aluminium improves the formability of an oxide film around the melt jet. The effect of addition of a small amount of Al into these three binary alloys on the spinnability was examined. Dendritic structures were observed in Ag-(5-30at%)Bi alloys, Ag-(5-30at%)Pb alloys and Ag-(5-30at%)Tl alloys. The relation between the secondary dendrite arm spacing and the mean cooling rates during soli … More dification interval were expressed as a function of the concentration of the solute atom that is Bi, or Pb, or Tl. The range of the secondary dendrite arm spacing was from 5 to 50mm corresponding to the cooling rates from 2 -50K/s. The dendritic structures of the ternary alloys containing Al were observed more clearly. The solidification temperature ranges of these three ternary alloys containing under 2at% Al decreased but those of the alloys containing over 5at% Al increased. The Micro-Vickers hardness of these three binary alloys decreased from 50 to 10 with increasing the concentration of the solute atom that is Bi, or Pb, or Tl in each binary alloy. Ag-Bi-5at%Al, Ag-Pb-5at%Al and Ag-Tl-5at%Al ternary alloys were superior to the binary alloys that do not include Al in spinnability. In the case of (Ag-5Pb)-5at%Al alloy, the continuous fiber of about 1m in length was produced at the spinning conditions of 0.075mm in nozzle diameter and of about 0.53rad in ejection angle of the melt jet into the rotating water layer. However in other spinning conditions and in other alloys, the maximum length of the obtained fiber was about 200mm. Less