Structure, microhardness, and strength of a directionally crystallized Al-Ge alloy

The structure, microhardness, and strength of binary directionally crystallized aluminum alloys with 35, 43, 53, 57, and 64 wt % germanium have been investigated. It has been shown that the eutectic microhardness is constant in the composition region under study. The microstrength of primary crystals of the solid solution of germanium in aluminum with the dendrite structure increases with increasing germanium concentration. However, the difference in the microhardnesses of the eutectic and dendrites, which was determined for each of compositions on the same specimen, does not exceed the measurement error. It has been assumed that the change in the strength of the alloy having the composition in the hypoeutectic region is determined by the redistribution of the volume fractions of the eutectic (alpha-Al and eutectic germanium) and the domains of primary crystals of the solid solution. This dependence can be described by the mixture rule. Above the eutectic composition, the alloy decomposes in a brittle manner; its strength is likely dependent not only on the content of the components, but also on the form and orientation of primary germanium crystals.