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Wang Q.,Jiangsu University of Science and Technology | Zhao Z.,Jiangsu University of Science and Technology | Zhao Y.,Jiangsu University of Science and Technology | Yan K.,Jiangsu University of Science and Technology | And 2 more authors.
Materials and Design | Year: 2016

Spray forming Al-Zn-Mg-Cu alloy has been welded successfully by underwater Friction Stir Welding (underwater FSW). The joint is defect-free with tensile strength of 406.06 MPa and improved elongation (1.96%). Microstructure of underwater joint has been improved in which the hard-etched area is eliminated compared with traditional joint. The microstructure of joints was observed by OM and SEM. EDS, DSC, XRD and TEM were applied to do further study on the evolution of strengthening phases. The results show that water cooling method has improved the thermal cycle of welding. The microstructure of joint and the strengthening mechanism of underwater joint had a close relationship with the effect of water cooling method. The system analysis of underwater FSW process has been illustrated. Water cooling method creates rapid cooling process to introduce GPII zone and reserve a large amount of needle-like semi-coherent structure MgZn2 which is {0001}η(η') ∥{111}Al dispersing in the matrix. The strength of joint has been enhanced by coherency strengthening. © 2016 Elsevier Ltd. Source


Wang Q.,Jiangsu University of Science and Technology | Wang Q.,Shanghai JiaoTong University | Zhao Z.,Jiangsu University of Science and Technology | Zhao Y.,Jiangsu University of Science and Technology | And 2 more authors.
Materials and Design | Year: 2015

In present work, the adjustment strategy of Underwater Friction Stir Welding (UFSW) parameters for spray formed 7055 aluminum alloy has been discussed by 3 groups welding experiment by changing rotation or traveling speed. The thermal cycles, microstructures, especially Reentrant Zone (RZ), tensile properties and micro-hardness of joints have been compared. The results show that the underwater joint which presents good properties has full weld nugget with wider and deeper RZ. It proves that the rotation speed has a wider adjustment range than traveling speed for UFSW process. In the water cooling environment, the fluidity of metal is weakened sharply. High rotation speed can ensure the fluidity of metal till the joint is filled completely that shows better properties. SEM&EDS and XRD results show that these joint keeps most of MgZn2. It indicates that a high rotation speed can be applied to UFSW process without worrying about overheating the joint. In the cooperation of high rotation speed and water environment, the joint is under a dynamic heat remedy process which makes the joint under a balance thermal cycles so that achieves better property. The parameter of high rotation speed and high traveling speed is recommended for UFSW. © 2015 Elsevier Ltd. Source


Xu J.-H.,Jiangsu University of Science and Technology | Zhao L.-J.,Jiangsu University of Science and Technology | Yu L.-H.,Jiangsu University of Science and Technology | Nie B.,Jiangsu University of Science and Technology | And 4 more authors.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2011

The industrial scale 7055 alloy billets were prepared by fully automatic controlled reciprocating spray forming technology. The effects of hot-extruded, double-stage solution and different aging treatments on the microstructure and mechanical properties of spray-deposited aluminum alloy were studied. It is shown that the spray-deposited 7055 aluminum alloy has the highest strength after the single-stage aging (120°C/24 h). The tensile strength, yield strength, hardness of HRB, extensibility and the conductivity are 725 MPa, 685 MPa, 96, 10.0% and 30% IACS, respectively. The results also show that the double stage aging leads to excellent plasticity and stress corrosion resistance, but the strength is low. With the aging temperature and aging time of the double aging increasing, the alloy strength decreases, the plasticity and conductivity increase. The optimum double-stage aging process through the analysis of orthogonal experiments is: 120°C/8 h +170°C/8 h. The alloy has excellent comprehensive properties after the double-stage aging treatment. The tensile strength, yield strength, hardness, extensibility and conductivity are 659 MPa, 630 MPa, 95 (HRB), 11.7% and 39% IACS, respectively. Compared with the single-stage aging treatment, the conductivity increases by 30%, stress corrosion resistance improves significantly. Source


Xu J.-H.,Jiangsu University of Science and Technology | Zhao L.-J.,Jiangsu University of Science and Technology | Shi L.-B.,Jiangsu University of Science and Technology | Zhang H.,Shanghai JiaoTong University | And 5 more authors.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2011

An industrial large-scale 7055 Al alloy billet was prepared by fully automatic controlled reciprocating spray formation technology, and the as-deposited aluminum alloy was joined by friction stir welding (FSW). The appearance, microstructure and mechanical properties of the joints were investigated by many kinds of experimental means. The results show that, the FSW joint which is 4 mm in thickness presents excellent appearance, defect-free, less distortion. The characteristics of the three distinct zones can be clearly identified, the joint tensile strength of 475 MPa reaches up to 77% of the base material's and that is much higher than that of the conventional fusion welding joints. Fracture region locates at the heat-affected zone. After the T6 heat treatment, the tensile strength decreases, but the elongation increases from 2.58% to 6.42%. Source


Xu J.-H.,Jiangsu University of Science and Technology | Wang G.-H.,Jiangsu University of Science and Technology | Yu L.-H.,Jiangsu University of Science and Technology | Li H.,Jiangsu University of Science and Technology | And 3 more authors.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2012

Slow strain rate tensile tests of the spray forming 7055 aluminum alloy with aging systems of T6 and three different duplex aging systems were done in the air and 3.5% (mass fraction) NaCl solution. The conductivities were tested and fracture morphologies of aged 7055 aluminum alloy were determined and observed by SEM. The stress corrosion cracking behavior of 7055 aluminum alloy with T6 and three duplex aging systems in the air and 3.5% (mass fraction) NaCl solution were studied. The results show that, stress corrosion cracking susceptibility of spray forming 7055 aluminum alloy is obvious only at some strain rate; Under the same aging system, stress corrosion cracking sensitivity of spray forming 7055 aluminum alloy is the biggest at the strain rate of 0.5×10-6 s-1 among four strain rates of 1.3×10-6, 0.8×10-6, 0.5×10-6 and 0.2×10-6 s-1. The stress corrosion cracking resistance of 7055-T6 aluminum alloy is worst than others. After the time of secondary ageing reaches 15 h, 7055 aluminum alloy is not sensitive to stress corrosion cracking; At the strain rate of 0.5×10-6 s-1 in the 3.5% (mass fraction) NaCl solution, the fracture way of spray forming 7055 alloy is sub-cleavage fracture, while in the air, the fracture way of sample is dimple fracture. Source

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