Electrochemical investigation of localized deformation of metals and the effective ductility of passive films of aluminium and its alloys

Studies have been made of the current transients when potentiostated pre-anodized metals are strained in 1% (NH4)2B4O7. Anodized films between 43 and 1000 Å have been studied on pure Al, alloy 7075 (typically, in wt-%, 5·5 Zn, 2·2 Mg, 1·2 Cu, 0·1 Cr, balance Al), in variously stress-corrosion-susceptible tempers, pure Al-7·5 Zn-2·5 Mg and pure Al-4 Cu·. Currents on Al and AlCu start to increase only on bulk plastic deformation. Currents on 7075 and AlZnMg increase immediately on straining. Thicker oxides on Al appear more brittle than thinner oxides. There is little variation with thickness in apparent oxide ducitility on 7075, however. This is because the oxide rupture is caused by localized metal deformation (microslip) even in the bulk plastic range. Apparent oxide brittleness correlates with stress-corrosion susceptibility for 7075 but not for AlZnMg or AlCu. In no case is susceptibility to oxide rupture per se the direct cause of susceptibility to stress corrosion. © 1971.

Duke Scholars

Author F. Hadley Cocks Thomas Lord Department of Mechanical Engineering and Materia ...