Heat treating characteristics of high strength Al-Zn-Mg-Cu alloys with and without silver additions

Abstract

Effects of the addition of 0.35 pct Ag on tensile properties of commercially-fabricated 2 in. thick plate were investigated with two 7075-type alloys and similar chromium-free compositions containing 0.35 pct Mn. Both rates of cooling during the quench from the solution heat treatment and rates of heating to precipitation heat-treating temperatures strongly affected relative strengths of the alloys. Alloys containing silver developed substantially higher strengths than the control alloys without silver when 0.125 in. (3.2 mm) thick specimens from the plate were rapidly quenched and rapidly heated to precipitation temperatures above 200∮F (92°) and isothermally precipitated. When the rapid quench was followed by slower heating to the precipitation temperature, however, both silver-free and silver-containing alloys developed comparable high strengths. When the full thickness plate was heat treated employing cooling and heating rates established by section size and standard commercial processing, silver had,relatively little effect on the mechanical properties. With lower quenching rates, alloys without silver developed higher strengths than their counterparts with silver.