Microstructural and mechanical characterisation of an Al-21.8 wt.% Ge brazing alloy with a globular morphology of the primary Al-rich phase

This paper is concerned with the microstructural and mechanical characteris ation of a hypoeutectic Al-Ge alloy designed to join the plasma facing comp onents of thermonuclear fusion reactors to permanently cooled substrates. T he alloy was prepared from pure aluminium and germanium by casting, hot rol ling and heat treatment above the eutectic temperature. This treatment lead s to a globular morphology of the primary Al-rich phase provided that the t hickness reduction during rolling is sufficient, about 20%. Increasing the rolling reduction, however, leads to liquid entrapment in the globules, the amount of which depends on the temperature in the semisolid range. The mec hanical behaviour of the material was determined in tensile tests at room a nd elevated temperature after various heat treatments in the semisolid stat e and compared with the mechanical properties after hot rolling. In additio n, compression tests were also carried out in the semisolid state. These te sts show that the globular materials deform under very low stresses without segregation of the liquid. A comparison is made with non-globular material s obtained simply by partial remelting of the as-cast alloy. (C) 1999 Elsev ier Science S.A. All rights reserved.