Effects of Natural Ageing Treatment on Mechanical, Microstructural and Forming Properties of Al 2024 Aluminum Alloy Sheets

In this study, the microstructural variations, mechanical properties and forming limit diagrams (FLD) of Al 2024 aluminum alloy sheet with the thickness of 0.81mm are investigated during natural ageing (T4) treatment. The most formability in Al 2024 can be achieved just after solution treatment, and it is better to perform the forming process, on this aluminum alloy sheet, in this condition. However, in industrial applications, there is usually a postponement for some hours after solution treatment to begin the forming process that it means the forming process should be done at the natural ageing condition. This condition decreases the formability of Al 2024 sheets. To monitor the properties variations in natural ageing condition, FLDs were determined after specific times (e.g., 0.5, 1.5, 4 and 24 hours). The variations in micro-hardness, yield strength, ultimate tensile strength and elongation at break were observed with changing the ageing time. The scanning electron microscope (SEM) investigations illustrated that density and size of precipitates were changed with ageing time. Moreover, the Nakazima test was utilized to study the forming limits considering the natural ageing condition. Results showed by increasing the ageing time, up to 4h, the majority of properties variations could be seen, and from 4h to 24h, the variations were changed slower.