Dislocation-mediated grain refinement mechanisms in 7005 aluminum alloy via cyclic extrusion and compression processing

Abstract 7005 aluminium alloy demonstrates excellent specific strength and good corrosion resistance, which renders it a material of considerable use in a variety of fields, including aerospace and transportation equipment manufacturing. The refinement of grain is of significant importance in enhancing its overall performance,particularly by improving its yield strength, tensile strength, hardness, ductility, fatigue resistance, and corrosion resistance. The present study employs Cyclic Equal Channel Compression (CECC)—a severe plastic deformation (SPD) technique that applies cyclic, high cumulative strain through equal channel geometry to refine grain structures while maintaining the overall specimen dimensions—technology, which combines the characteristics of repeated compression and isometric extrusion, to subject 7005 aluminium alloy, after homogenization annealing, to four passes of plastic deformation processing at room temperature. The microstructure was systematically characterised using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results demonstrated that following four passes of CECC, the alloy exhibited an average grain size of approximately 1.5 μm, with localized grain refinement to 150–250 nm, forming an ultra-fine grain structure. The microstructure of the material was found to contain a number of typical plastic deformation structural features, including dislocation tangles, dislocation cells, dislocation walls, slip lines, and microbands. Subsequent analysis indicated that the refinement of grains in the 7005 aluminium alloy during CECC was predominantly driven by dislocation slip and dislocation segmentation. This study provides an effective processing pathway and theoretical foundation for microstructural control and performance optimisation of high-strength aluminium alloys.