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Xu W.F.,Northwestern Polytechnical University | Liu J.H.,Northwestern Polytechnical University | Chen D.L.,Ryerson University | Luan G.H.,China Center Beijing Technology Co. | Yao J.S.,Shanghai Aerospace Equipments Manufacturer
Scripta Materialia | Year: 2012

The microstructure and cyclic deformation behavior of three slices of a thick plate of friction-stir-welded Al-Cu alloy were investigated. Friction stir welding resulted in a composite-like nugget zone consisting of fine particles uniformly dispersed in the recrystallized fine-grained matrix. The top slice had larger grains, smaller particles, higher hardness, stronger cyclic hardening, higher hysteresis energy and lower fatigue life than the bottom slice. Fatigue cracks initiated from near-surface particles in the low-hardness zone, and propagated via striation formation mechanisms along with particle cracking. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Fu R.,Yanshan University | He M.,China Center Beijing Technology Co. | Luan G.,China Center Beijing Technology Co. | Dong C.,China Center Beijing Technology Co. | Kang J.,Yanshan University
Journal of the Chinese Society of Corrosion and Protection | Year: 2010

The microstructures of friction stir welded (FSW) joint of 2024 aluminum alloy were examined by using optical microscope and transmission electron microscope. The corrosion behaviors of the joint were investigated by method of acid salt spray. The analysis results of microstructure show that the arc stripe is the main feature on the surface of the weld seam due to the extrusion action of the shoulder of the stir tool. The grain and second phase particles are also refined. The second phase particles are mainly composed of Al2CuMg(S phase) and CuAl2(θ phase). The corrosion test shows that the resistance to corrosion of FSW seam is lower than that of base metal pure aluminum layer. There exists an unevenness for the corrosion of the FSW seam. The corrosion initially results from pitting corrosion and finally develops to exfoliation. Source

Xu X.-D.,Tianjin University of Technology | Yang X.-Q.,Tianjin University of Technology | Zhou G.,Tianjin University of Technology | Tong J.-H.,China Center Beijing Technology Co.
Hangkong Cailiao Xuebao/Journal of Aeronautical Materials | Year: 2012

Microstructures and the fatigue performances of AA6061-T6 friction-stir-welded overlap joints were investigated. It was shown that the grain deformation of TMAZ was more serious in the retreating side than that in the advancing side. All the fatigue fracture sites of specimens were initiated at the more serious hooking defect, in which the up-trend was larger. When R was equal to 0.1, the fatigue strength Δσ k of Aluminum alloy FSW overlap joints was 18.25 MPa for the 95% survival probability, which meant an increase of 31.11% as compared with the Δσ k=13.92 MPa of Aluminum alloy fusion overlap welded joints. Besides, it was observed that the slope value m for the S-N curve of the FSW joints was 5.39, which was higher than that of the fusion welded joint set to 3.0-3.5.So the FSW joint had better fatigue strength than that of the fusion welded joints in the long life region of fatigue performance. Fatigue cracking was initiated at the surface defects or strengthening phase particles locating at the bottom of the upper plate, which were corresponded to the hooking position. Source

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