The effect of cold rolling, double aging and overaging processes on the tensile property and precipitation of AA2024 alloy

Abstract

In this investigation, the effect of the amount of cold rolling on the single stage and double stage aging responses of an AA2024 aluminum alloy was assessed. Two cold deformation amounts were applied on the solution heat treated AA2024 sheets. The effect of these deformation on a two-step short time aging performed at low, and subsequently at high temperatures, were studied in terms of precipitation and mechanical properties variations. As well, the effect of rolling percentage on the singe stage of overaging was assessed. Microstructural evolution was studied by optical microscope (OM) and Field Emission Scanning Electron Microscope (FE-SEM) and Transmission Electron Microscope (TEM). Mechanical properties were assessed through tensile testing and microhardness variation. Electrical conductivity (EC) measurements were also made to track the changes of precipitation condition. Results showed that applying cold rolling substantially increased the strength and slightly reduced ductility. In addition, performing the cold rolling created better condition, through dislocation generation, for the strengthening precipitates. Under such a condition, a short time aging through double aging process provided higher strength level compared with the long aging process of the overaging treatment. TEM studies showed the development of sub-structure through dislocation cells formation for the cold deformed cases. It also showed that very small size S′ hardening precipitates are present for the highest level of strength/hardness achieved in the double aging process. Also TEM studies suggested that no morphological changes occurred in the highest strength level achieved for the double aged conditions. Microhardness and electrical conductivity variation followed the same trend as the strength variation, for both the double aging process and the overaging condition.

Keywords

• AA2024 aluminum alloy
• TEM
• Mechanical properties
• Double aging
• Precipitation
• Cold rolling