銀-アルミニウム系合金の燒戻硬化に就て

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The equilibrium diagram for the silver-rich Ag-Al system has been studied by several persons, but little is known on its hardening characteristics. In the present paper, the temper hardening of these alloys is mainly dealt with, and some particular points as to the equilibrium diagram, which are necessary for our investigation, are examined. From the results of the examination of the Ag-Al system regarding the thermal expansion, differential dilatation and microscopic structure, it is concluded that the boundary line between α+γ and γ somewhat differs from that which was given in previous papers, and it lies virtually on the ordinate of about 7.7% aluminium. Specimens quenched from the α+γ range and etched by a solution of twenty parts of water and one part of saturated solution of chromic acid in sulphuric acid, distinctly show their eutectic structures. The temper-hardening of these alloys occurs in a range from 5.6 to 9.5% of aluminium in silver, and if the alloys are quenched at a temperature between 450°and 720℃. and tempered at a temperature from 200℃. to 350℃., a Vickers hardness numbers from 300 to 365 is obtained. The hardening velocity of the alloys containing aluminium of more than 7.7% which corresponds to the constituent of Ag_3Al differs from that of the alloys containing aluminium of less than that value; the former rapidly reached the maximum hardness after tempering, whilst the latter requires at least several hours. The alloy quenched from a temperature over 600℃., after having been reasonably tempered, has a hardness higher than that quenched from a temperature lower than 600℃., presumably, owing to refining of grains due to the eutectic reaction. The hardening of the alloy in question is caused by the hard constituent of β' which is produced by the reaction between α and γ due to tempering, whilst α and γ are obtained by quenching. On the other hand, the increase in hardness caused by the precipitation out of supersaturated solid solution is not likely to occur, though it is the most general case.
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銀-アルミニウム系合金の燒戻硬化に就て

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