Intergranular fracture caused by trace impurities in an Al-5.5 mol% Mg alloy

A coarse-grained Al-5% Mg alloy, which does not show high temperature embri ttlement, is successfully prepared using high purity raw materials and a gr aphite crucible. By preventing the contamination of sodium and hydrogen, it becomes possible to examine separately the effects of various trace elemen ts on hot ductility in the Al-5% Mg alloy. Sodium, calcium, or strontium of 2 mol ppm brings about the high temperature embrittlement based on intergr anular fracture, while lithium of 4 mol ppm does not. Sodium is the most hi ghly embrittling among such detrimental elements. The detrimental effect of such impurity is due to its segregation to grain boundaries. Further, the embrittlement caused by sodium or strontium of 2 mol ppm is greatly suppres sed by an addition of more than 1000 mol ppm of silicon which scavenges tho se detrimental elements from grain boundaries. (C) 2001 Acta Materialia Inc . published by Elsevier Science Ltd. All rights reserved.