Achieving high strength and ductility in double-sided friction stir processing 7050-T7451 aluminum alloy

In this paper, a novel approach named double-sided friction stir processing (DFSP) was proposed to prepare 7050-T7451 aluminum alloy plates, and effects of solution treatment (ST) on microstructures and mechanical properties of DFSP were investigated. The solution treatment at 470 °C for 4.5 h was employed. 7050-T7451 and 7050-ST aluminum alloy plates were used for DFSP, and their experimental results were compared. A significant grain refinement to an average 1.5-2.2 µm was attained by DFSP for both 7050-T7451 and 7050-ST plates. The microstructure exhibits a bimodal character which consists of fine grains with the size of 1-6 µm and ultrafine grains with the size of ~1 µm. The precipitated particles in the SZ of T7451-DFSPed and ST-DFSPed plates are MgZn2 and MgAlCu/Al7Cu2Fe. Compared with the T7451-DFSPed plate, the ST-DFSP one shows a higher dissolution degree of Mg and Zn elements, and most dispersoid are retained as η′ phase, additionally, the homogenization of the microhardness distribution of the ST-DFSP plate is improved and a higher tensile strength is obtained while good ductility is maintained.