Effects of solution treatment on the microstructure and mechanical properties of naturally aged EN AW 2024 Al alloy sheet

Abstract

The solution experiments on cold rolled 2024 Al sheet with a 1070 Al coating were carried out at various temperatures and holding time. The effects of solution parameters on the microstructure evolution and mechanical properties were studied. The results showed that the alloying elements diffused from the 2024 Al matrix to the 1070 Al coating, following the peak-valley pattern. The cold rolled 2024 Al sheet mainly have the second phases of Al2Cu, S (Al2CuMg), Si, Mg2Si, and the impurities of AlFeMnSi, AlCuFeMnSi, AlCuFeMn, and the amount of them was reduced with increasing solution temperature or holding time. T (Al20Cu2Mn3) had precipitated before aging, and only the Cu–Mg clusters were formed during the natural aging, which should be the main strengthening mechanism. The grain structure was elongated during cold rolling, while the static recrystallization and grain growth occurred during the solution treatment. The ultimate tensile strength, yield strength and elongation were gradually enhanced with increasing the solution temperature to 510 °C. When the solution temperature is further increased to 530 °C, the elongation was obviously decreased due to the over-burning. Moreover, it was found that the solution temperature had much stronger effects on the mechanical properties than that of the holding time.