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 characterisation of a hypoeutectic Al-Ge alloy designed to join the plasma facing components of thermonuclear fusion reactors to permanently cooled substrates. The alloy was prepared from pure aluminium and germanium by casting, hot rolling and heat treatment above the eutectic temperature. This treatment leads to a globular morphology of the primary Al-rich phase provided that the thickness 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 mechanical behaviour of the material was determined in tensile tests at room and elevated temperature after various heat treatments in the semisolid state and compared with the mechanical properties after hot rolling. In addition, compression tests were also carried out in the semisolid state. These tests show that the globular materials deform under very low stresses without segregation of the liquid. A comparison is made with non-globular materials obtained simply by partial remelting of the as-cast alloy.