Societies and Academies

Abstract

LONDON.Institute of Metals, Mar. 13.-P. Saldau: Special properties of eutectics and eutectoid alloys in binary metallic systems. As regards hardness and electrical resistance, the eutectic occupies an abnormal position on the property-composition curve, even in drastically annealed alloys. For coalescence to occur, an excess of one of the phases is necessary.-F. Hargreaves and R. J. Hills: Work-softening and a theory of inter-crystalline cohesion. For work-softening there must be more than one phase present and, roughly, both constituents must undergo spontaneous annealing after working at air temperature. A theory of inter-crystalline cohesion is outlined. Briefly, it postulates the existence of a transition zone between two orientations. Work-hardening and work-softening are identical phenomena concerning the early stages of the latter. The pronounced softening caused by heavy working is attributed to interphase boundary action and the retention of the individual phases in a quasi-viscous condition.-P. J. Durrant: The constitution of the cadmium-rich alloys of the system cadmium-gold. The constitution of the alloys of cadmium and gold from 0 to 48 atoms per cent of gold has been reinvestigated by thermal and micro-graphic analysis. Saldau's equilibrium diagram, published in 1915, has been modified. A new area of solid solution has been detected (phase III) which lies in the field described by Saldau as containing j8 +7. This solid solution undergoes two polymorphic changes-one at about 500° C., and the other at about 375° C., the latter being analogous to the change in the /3-phase of brass at 460° C. No evidence was obtained for the existence of the compound AuCd3 at the liquidus, but the form of the equilibrium diagram suggests the existence of two compounds, Au2Cd5 and Au2Cd3, both of which are much dissociated at high temperatures.-Marie L. V. Gayler and G. D. Preston: The age-hardening of some aluminium alloys. Five typical aluminium alloys containing copper, magnesium silicide, or both, have been examined. Changes in density and lattice parameter which take place during ageing suggest that precipitation from solid solution takes place. X-ray analysis shows also that the crystals themselves are in a disturbed state, which is gradually relieved by further ageing at high temperatures. The increase in electrical resistance on ageing corresponds to this distortion of the space lattice of the solid solution, caused by the presence of minute particles due to the decomposition of the solid solution. - Clement Blazey: Brittleness in arsenical copper (2). Under certain conditions, about 0'004 per cent of bismuth can produce a susceptibility to brittleness. The conditions are: plain melting under charcoal of arsenical copper of the quality used, followed by poling and the addition of bismuth before casting. The addition of phosphorus after bismuth destroys the susceptibility or it may be removed by remelting.-W. Hume-Rothery and E. 0. Rounsefell: The system magnesium-zinc. The equilibrium diagram of the system magnesium-zinc has been investigated in the range 0 to 70 atomic per cent magnesium. Particular attention has been paid to the structure of the solid alloys and the limits of solid solution in the various phases. The compound MgZn6, discovered by Chadwick, and MgZn2, discovered by Grube, have been confirmed. A new compound, MgZn, has been shown to exist, and this also is of fixed composition. It may be distinguished from MgZn2 by means of Benedicks' reagent. The compound is formed at 354° C. by a peritectic reaction between MgZn2 and liquid. On the practical side, the present work shows that in elektron metal, and similar alloys, any zinc present in excess of that contained in solid solution in magnesium will exist in the form of the new compound MgZn, and not, as previously supposed, as MgZna.