Study on Microstructure Evolution Mechanism of Gradient Structure Surface of AA7075 Aluminum Alloy by Ultrasonic Surface Rolling Treatment

• Published in: Materials Vol. 16; no. 16; p. 5616
• Main Authors: Fu, Lei, Li, Xiulan, Lin, Li, Wang, Zhengguo, Zhang, Yingqian, Luo, Yunrong, Yan, Shisen, He, Chao, Wang, Qingyuan
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.08.2023; MDPI
• Subjects: AA7075 aluminum alloy; Acids; Alloys; Aluminum; Aluminum alloys; Aluminum base alloys; Compressive properties; Corrosion; Deformation; Dislocation density; Evolution; Frictional wear; gradient structure; Grain refinement; Grain size; Grain size distribution; High resistance; High strength alloys; Industrial equipment and supplies industry; Iron compounds; Low cycle fatigue; Mechanical properties; Metal fatigue; Microstructure; microstructure evolution mechanism; Morphology; Nanocrystals; Nanostructured materials; Plastic deformation; Precipitates; Scanning electron microscopy; Skin pass rolling; Specialty metals industry; Strain hardening; Surface layers; Surface properties; ultrasonic surface rolling treatment; United States; China; Beijing China; United States > US
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma16165616

The materials with grain size gradient variation on the surface, which were prepared with mechanical-induced severe plastic deformation, always show high resistance to high and low cycle fatigue and frictional wear because of their good strength–ductility synergy. The ultrasonic surface rolling treatment (USRT) has the advantages of high processing efficiency, good surface quality, and large residual compressive stress introduced to the surface after treatment. The USRT was used to prepare aluminum alloy (AA7075) samples with a surface gradient structure; meanwhile, the microstructural evolution mechanism of the deformation layers on the gradient structure was studied with XRD, SEM, and TEM. The microstructure with gradient distribution of grain size and dislocation density formed on the surface of AA7075 aluminum alloy after USRT. The surface layer consists of nanocrystals with random orientation distribution, and high-density dislocation cells and subgrains formed in some grains in the subsurface layer, while the center of the material is an undeformed coarse-grained matrix. The results show that the dislocation slip dominates the grain refinement process, following the continuous cutting and refinement of dislocation cells, subgrains, and fragmentation of the second precipitates. This study systematically clarified the mechanism of grain refinement and nanocrystallization on the surface of high-strength aluminum alloys and laid a theoretical foundation for further research on mechanical behavior and surface friction and wear properties of high-strength non-ferrous materials with gradient structure.