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Liang Z.,Shanghai JiaoTong University | Liang Z.,University of Hong Kong | Chen K.,Shanghai JiaoTong University | Wang X.,Shanghai JiaoTong University | And 4 more authors.
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2013

Friction stir welding (FSW) is a promising solid-state joining technique for producing effective welds between Al alloy and Mg alloy. However, previously reported Al/Mg dissimilar FSW joints generally have limited strength or barely any ductility with relatively high strength, which was blamed on the brittle intermetallics formed during welding. In this study, effective joints with comparably high strength (163 MPa) and large elongation (∼6 pct) were obtained. Three crucial/weak zones were identified in the welds: (1) Al/Mg bottom interface (BI) zone that resulted from the insufficient materials' intermixing and interdiffusion; (2) banded structure (BS) zone which contains intermetallic particles possibly formed by constitutional liquation; and (3) softened Al alloy to the retreating side (SAA-RS) zone due to the dissolution and coarsening of the strengthening precipitates. Three fracture modes observed in the tensile specimens perpendicular to the weld seam were found closely related to these zones. Their microstructure evolution with the change of tool rotational speed and tool offset was characterized and the consequent effect on the fracture mode alteration was studied. It turned out that enhancing the strengths of all these zones, but keeping the strength of the SAA lowest, is an effective way for enhancing ductility while keeping comparatively high strength in Al/Mg FSW joints. Also, suggestions for further improving the mechanical property of the Al/Mg dissimilar FSW joints were made accordingly for practical applications. © 2013 The Minerals, Metals & Materials Society and ASM International. Source


Chen B.,Shanghai JiaoTong University | Chen K.,Shanghai JiaoTong University | Hao W.,Shanghai JiaoTong University | Liang Z.,Shanghai JiaoTong University | And 3 more authors.
Journal of Materials Processing Technology | Year: 2015

Small-dimension Al3003 pipe and pure copper pipe of thin wall (Al: 1.5 mm; Cu: 1 mm) and small diameter (19 mm) were successfully joined by a developed welding method with a specially-designed friction stir welding (FSW) system. A distinctive temperature history due to heat accumulation was identified as an important feature for FSW of small-dimension pipes, leading to distinctive variations of surface condition, macro-/micro-structure along the circumferential weld seam. Hardness distribution, tensile strength, ductility and fracture modes were found to change correspondingly along the weld seam. © 2015 Elsevier B.V. All rights reserved. Source


Shi H.,Shanghai JiaoTong University | Chen K.,Shanghai JiaoTong University | Liang Z.,University of Hong Kong | Dong F.,Special Welding Technology Center | And 4 more authors.
Journal of Materials Science and Technology | Year: 2016

Dissimilar friction stir welding (FSW) between aluminum and magnesium alloy was performed, using various tool rotational speed (TRS) at a fixed travel speed, with tool offset to aluminum to investigate the formation of intermetallic compounds (IMCs) in the banded structure (BS) zone and their effect on mechanical properties. Large quantities of IMCs, in the form of alternating bands of particles or lamellae, were found in the BS zone, where drastic material intermixing occurred during FSW. The BS microstructural characters in terms of the morphology of the bands and the quantity and distribution of IMC particles varied with TRS. All welds exhibited brittle fracture mode with their fracture paths propagating mainly in/along the IMCs in the BS. It is shown that these BS microstructural characters have significant effect on the mechanical properties of the joints. Suggestions on tailoring the BS microstructure were proposed for improving the strength of the BS zone and the final mechanical properties of the Al/Mg FSW joints. © 2016. Source


Li Y.,Special Welding Technology Center | Feng X.,Special Welding Technology Center | Zhang D.,Special Welding Technology Center | Cui F.,Special Welding Technology Center
Hanjie Xuebao/Transactions of the China Welding Institution | Year: 2015

The lock butt joint of 0Cr15Ni5Cu4Nb stainless steel of 7 mm in thickness was welded with high power fiber laser, the characterizations of welding process were studied by analyzing the influence of different welding parameters on the weld quality, mechanical properties and microstructure. Result shows that porosity is the main defect in the weld, and the negative defocus and high welding speed can prevent porosity from formation effectively. There is an increase in the hardness of the weld, and the top and bottom weld have higher hardness than the central weld does. The tensile strength of the joint is 970 MPa, and higher than that of base metal, but its impact toughness is slightly lower, is 89% of that the base metal. Weld microstructure consists of martensite, retained austenite and δ-Fe, and the central weld has more δ-Fe than the top weld. Martensitic transformation was not sufficient in the central weld, the microstructure of HAZ is mainly quenched martensite with small grain. ©, 2015, Harbin Research Institute of Welding. All right reserved. Source

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