Kinetics of precipitation in aluminum alloys during continuous cooling

Abstract

Rate of cooling from the solution treatment temperature has a pronounced effect on corrosion behavior and mechanical properties of precipitation-hardenable aluminum alloys. This effect is attributed to loss of vacancies and to precipitation of solute during the quench. Analysis of data for aluminum alloys indicates that precipitation rate is an explicit function of temperature and the amount of solute remaining in solution; consequently, precipitation during cooling is additive and can be evaluated by integrating this function. A method is presented whereby type of corrosion attack or mechanical properties can be accurately predicted from the cooling curve and a C-curve for the alloy. Because the actual cooling curve is considered, the method is applicable regardless of the complexity of the cooling conditions. Also presented is an improved method of accurately determining C-curves using either interrupted or continuous quenching techniques. C-curves describing type of corrosion attack in 2024-T4 sheet and loss in mechanical properties of 7075-T6 sheet are presented.