Abstract
The effects of twenty-one kinds of less than 0.5 at% additional elements and heat treatments on the fracture characteristics of Al-2.5 at% Zn-2 at% Mg alloy were mainly studied by the measurements of tensile properties and resistance to stress-corrosion.
The additions of more than 0.01 at% In and 0.03 at% Cd weaken cohesivity across grain boundaries of Al–Zn–Mg alloy quenched from 465°C. Higher solution temperature and 0.03∼0.1 at% Ag also weaken the cohesivity in the fully aged conditions. The additions of Zr, Mo, V, Cr and Mn improve not only grain boundary embrittlement but the resistance to stress-corrosion when these elements are finely distributed as insoluble compounds and are effective for the refining of recrystallized grains. Slow quenching after solution treatment deteriorates ductility as well as strength, but improves the resistance to stress-corrosion. This may be due to the development of mechanically weak, solute depleted zones along grain boundaries and of the associated wide precipitate-free zones.
