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The microstructure and texture of materials significantly influence the mechanical properties and fracture behavior; the effect of microstructure in different zones of friction stir-welded joints of 7A52 aluminum alloy on fracture behavior was investigated in this paper. The microstructural characteristics of sections of the welded joints were tested using the electron backscattered diffraction (EBSD) technique. The results indicate that the fracture is located at the advancing side of the thermomechanically affected zone (AS-TMAZ) and the stir zone (SZ) interface. The AS-TMAZ microstructure is vastly different from the microstructure and texture of other areas. The grain orientation is disordered, and the grain shape is seriously deformed under the action of stirring force. The grain size grows unevenly under the input of friction heat, resulting in a large amount of recrystallization, and there is a significant difference in the Taylor factor between adjacent grains and the AS-TMAZ–SZ interface. On the contrary, there are fine and uniform equiaxed grains in the nugget zone, the microstructure is uniform, and the Taylor factor is small at adjacent grains. Therefore, the uneven transition of microstructure and texture in the AS-TMAZ and the SZ provide conditions for crack initiation, which become the weak point of mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract The long-lasting chrome-free, corrosion-resistant surface treatment of aluminum is of crucial importance. In our work, we prepared an intrinsic self-repairing and self-antibacterial film of single step in-situ grown inorganic lithium (Li), aluminum (Al)-containing layered double hydroxides film modified by 2-guanidinosuccinic acid (denoted as GLDHs) on the surface of 6 N01-T5 Al alloy by a facile method with enhanced corrosion protection performance. A series of electrochemical tests and neutral salt tests (NSS) showed that the corrosion resistance performance of GLDHs was significantly improved as compared with blank LiAl-LDH film. Interestingly, an artificial defect in the GLDHs film exhibited remarkable performances of self-repairing. After immersion in 3.5 wt% NaCl solution for certain time, new LiAl-LDH film at the Al alloy surface were formed, which was characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), inductive coupled plasma emission spectrometer (ICP), elemental analyzer, polarization curves, electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). A self-repairing mechanism was proposed and discussed. Furthermore, GLDHs also exhibited excellent self-antibacterial activity toward Escherichia coli and Bacillus subtilis. The high self-antibacterial performance of GLDHs film could attribute to the modified 2-guanidinosuccinic acid. Our full demonstration of the multifunctional GLDHs film is considerably beneficial to the researchers to further understand its potential for the practical application in the field of corrosion protection of aluminum and aluminum alloy. Highlights • Li-Al layered double hydroxides (LDHs) film on aluminum alloy. • Multifunctional conversion film with enhanced corrosion protection property. • Excellent self-repairing property and the possible mechanism. • Excellent self-antibacterial property and the possible mechanism. [ABSTRACT FROM AUTHOR]