RESUMO
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.
RESUMO
The friction stir welding (FSW) parameters were designed in this study by orthogonal experimental method. The microstructure, mechanical properties and corrosion behavior of corresponding FSW joints of 5083 aluminium alloy (AA5083) were also investigated. Scanning Kelvin probe force microscopy (SKPFM) was employed to study local potential differences on the FSW joint. Results showed that the welding parameters greatly influenced the FSW joint properties of the AA5083. The ratio of rotation speed to welding speed (n/v) mainly affected the mechanical properties of the joint. The tensile strength for the joint was reduced when welded with too large or too small n/v. The hardness of all FSW joints was characterized with similar 'W-shaped,' and minimum hardness value appeared on advancing side of the heat affected zone. Different heat input and agitation intensity caused heterogeneous microstructure for the AA5083 FSW joint, which led to differences in passivation properties of weld nugget zone, thermo-mechanically affected zone and heat-affected zone. Susceptibility of the AA5083 FSW joint to pitting corrosion was attributed to the difference of relative potential between the intermetallic phase and Al matrix.