Effect of 3.5 wt% NaCl and Cathodic Charging on the Atomic Strain Distribution of a Plastically Deformed AA 7004

Abstract

The effects of environments in altering the atomic strain distribution in AA 7004 while subjected to slow strain rate testing to environmentally assisted cracking are investigated. Two different temper conditions—one where predominantly G.P. zones are present and the other with predominantly η′/η precipitates were chosen for the present study. Three different test environments—glycerol (Gly), 3.5 wt% NaCl (OCP), and 3.5 wt% NaCl with 100 mV cathodic charging vs. open-circuit potential (CP) were used. Under the above environmental conditions, the alloy aged at 140°C for 24 h, containing predominantly G.P. zones, showed the existence of the tensile nonshear components of the strain. On the other hand, the alloy aged at 140°C for 48 h, containing predominantly η′/η precipitates, showed only one of the two nonshear strain components that were tensile in nature, with a simultaneous reduction in the shear component of strain. The work highlights that the effects of the environment on the deformation behavior of the alloy are evident by way of alterations in strain distribution at the atomic level, which could possibly explain the increase in dynamic recovery for the microstructure containing primarily the G.P. zones, and the decrease in dynamic recovery for microstructures consisting predominantly of η′/η precipitates.