Grain Boundary Deformation and Fracture of a Fine Grained, High Purity Al-2% Mg Alloy at 150° C (423K)

Abstract

Intercrystalline deformation and fracture at elevated temperatures are well established phenomena, and are relatively well defined in terms of temperature, stress and grain size. Grain boundary sliding, leading to intercrystalline fracture, is usually considered to be an embrittling behavior, and worsens with decreasing strain rate, decreasing grain size and increasing temperature. Very coarse grained metals and alloys avoid intercrystalline failures even at very high temperatures by undergoing slip and slip band deformation, even up to the melting temperature. Based on the rule that the slip band spacing is inversely proportional to the stress, coarse grained structures can accommodate coarse slip band spacings to very high temperatures. Following this reasoning, a high purity Al-2% Mg alloy, prepared with a grain size finer than about 10 mm, undergoes grain boundary sliding, minor grain boundary migration, and intercrystalline cracking at 150° C (423K). The extent of grain boundary sliding and cracking are a function of the grain size and the stress.