Commercial 7075-T6 aluminum alloy was subjected to friction stir welding (FSW), resulting in development of a fine-grained structure with average size of about 3 mm in the nugget zone. Static annealing at temperatures ranging from 623 to 773 K for 30 min showed that the fine grain microstructure was stable at temperatures not higher than 723 K. Increase in annealing temperature up to 773 K led to an abnormal grains growth, followed by the development of mm-scale grains. The specimens obtained from the nugget zone demonstrated a superplastic behavior at temperatures ranging from 623 to 723 K and at strain rates ranging from 1 Â 10 À4 to 1 Â 10 À2 s À1 . Large elongation of about 440% was observed at a temperature of 673 K and at a strain rate of 1 Â 10 À3 s À1 .

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The aim of this study was the investigation of the effect of different Y 2 O 3 additives on wear resistance of the hypereutectic Fe-Cr-C hardfacing coatings. The microstructures were observed by optical microscopy, field emission scanning electron microscopy and transmission electron microscopy, respectively. Meanwhile, the hardness was measured and the wear resistance was evaluated. Finally, the role of Y 2 O 3 was discussed. The microstructures of the coatings consist of the primary (Cr, Fe) 7 C 3 carbide and eutectic structure [austenite ? (Cr, Fe) 7 C 3 carbide]. Moreover, Y 2 O 3 can refine the M 7 C 3 carbide and improve the wear resistance of coatings obviously. Y 2 O 3 can absorb at the surface of the M 7 C 3 carbide and improve the wear resistance of the hypereutectic Fe-Cr-C hardfacing coatings.

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Vickers hardness of friction stir welded 7075-T6 and 7075-O aluminum alloy plates were investigated. During welding, the tool rotation and tool traverse speeds were 1500 rpm and 300 mm/min, respectively. In order to study the anisotropy in the welded joints, the joints were welded in directions parallel and right angle to the rolling direction. Defect-free joints were obtained under the above condition. A fine and equiaxed recrystallised microstructure with grain size of approximately 3 m m was formed in the stir zone of the joints. Anisotropy in welded joints along the welding directions was not detected in terms of the microstructural characteristics of the joints. After friction stir welding, the Vickers hardness of the stir zone of the T6 joints decreased, but that of the O joints increased. On the other hand, after natural aging for 5 months, the Vickers hardness of the stir zone of the T6 joints increased and closely reached the hardness level of the base metal, while the Vickers hardness of the stir zone of the O joints increased further. From the above-mentioned Vickers hardness distributions, no anisotropy was observed along the welding direction. The above-mentioned behavior in hardness of the joints was discussed briefly on the basis of the Hall-Petch relation as well as other strengthening mechanisms.

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This work aims to reveal the effects of 3D roughness parameters of sandblasted surfaces on bond strength between thermal spray coatings and substrates. The investigation was carried out on the surface of AISI 4140, which were pretreated with automatic-sandblasting system. 3D topography and roughness parameters were analyzed by a 3D optical profiler. The bond strength of WC-12Co coatings was measured using a pull-off test method. Scanning electron microscope revealed that the morphology of the surface after sandblasting was rough. Furthermore, the surface topography was characterized by several irregular peaks and pits with different directions and no fixed orientation randomly distributed on sandblasted surface. The average values for surface roughness Sa = 4.84 ± 0.34 μm and bond strength = 32.8 ± 2.8 MPa were obtained. In terms of 3D roughness parameters, Sa, Sdr, Sdq and Sq were found to have more significant impact on affecting the bond strength, showing a nonlinear regression relationship. Furthermore, bond strength was positively correlated with Sa, Sdr and Sdq, while inversely proportional to Sq. This confirmed that a greater surface roughness of a sandblasted surface was not more conducive to the improvement of bond strength. The influence mechanism of each parameter was discussed, which was consistent with the regression mathematical model.