Quench factor analysis of aluminium alloys

Abstract

A model was developed almost 20 years ago which described how precipitation during the quench affected the development of properties of aluminium alloys during subsequent aging treatment. This model was the basis for an analytical process, known as quench factor analysis, that was used to predict the effects of quench path on corrosion characteristics and strength. The purpose of this paper is to provide a theoretical basis for the model and to review how quench factor analysis has been used in solving industrial problems. Several investigators have confirmed that quench factor analysis is an effective predictive method for all quenching conditions save one. The exception is when material has been quenched below the knee of the C-curve and subsequently reheated above the knee before the quench is complete. Applications include the design of quench systems, the development of quench practices which optimize combinations of high strength and low residual stress and distortion, and predictions of the magnitude of loss in strength as a result of unsuitable quenching conditions. By combining quench factor analysis with homogeneous nucleation theory, interactions between quenching and aging conditions have been clarified, and aging treatments have been developed which minimize the low and variable strengths caused by less than ideal quenching conditions. Quench factor analysis also adequately describes the rate of loss in toughness of an AA 6000 series extrusion alloy for those cooling conditions which produced commercially significant loss in strength. The latest use of quench factor analysis is in a specification for quenchants for aluminium alloys. MST/573