An attempt has been made to improve the corrosion resistance of friction stir welded joints of 7075 aluminum alloys by micro-arc oxidation（MAO）, and the effects of Na2Si O3 concentration in electrolyte on the corros...An attempt has been made to improve the corrosion resistance of friction stir welded joints of 7075 aluminum alloys by micro-arc oxidation（MAO）, and the effects of Na2Si O3 concentration in electrolyte on the corrosion resistance of the coatings were discussed. Morphology and phase constituents of the MAO coatings produced in electrolyte with different Na2SiO3 concentrations were analyzed by scanning electron microscopy, confocal laser scanning microscopy and X-ray diffraction. Electrochemical tests were conducted to evaluate the corrosion resistance of the coatings. The results show that the corrosion resistance of the coated joints is much better than that without the ceramic coating, and the ceramic coating produced in the electrolyte with Na2SiO3 concentration 20 g/L showed better corrosion resistance than the others.展开更多
The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion（EXCO） solution. Electrochemical measurements（open circuit potential, po...The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion（EXCO） solution. Electrochemical measurements（open circuit potential, potentiodynamic polarization curves, and electrochemical impedance spectroscopy）, scanning electron microscopy, and energy dispersive spectroscopy were employed for analyzing the corrosion mechanism. The results show that, compared to the base material, the corrosion resistance of the friction-stir welds is greatly improved, and the weld nugget has the highest corrosion resistance. The pitting susceptibility originates from the edge of Al-Cu-Fe-Mn-Si phase particles as the cathode compared to the matrix due to their high self-corrosion potential. No corrosion activity is observed around the θ phase（Al2Cu） after 2 h of immersion in EXCO solution.展开更多
The fatigue properties of friction stir welded （FSW） butt joint and base metal of MB8 magnesium alloy were investigated. The comparative fatigue tests were carried out using EHF-EM2OOK2-070-IA fatigue testing machin...The fatigue properties of friction stir welded （FSW） butt joint and base metal of MB8 magnesium alloy were investigated. The comparative fatigue tests were carried out using EHF-EM2OOK2-070-IA fatigue testing machine for both FSW butt joint and base metal specimens. The fatigue fractures were observed and analyzed using a scanning electron microscope of JSM-6063LA type. The experimental results show that the fatigue performance of the FSW butt joint of MB8 magnesium alloy is sharply decreased. The conditional fatigue limit （2 x 106） of base metal and welded butt joint is about 77.44 MPa and 49. 91 MPa, respectively. The conditional fatigue limit （2 x 106 ） of the welded butt joint is 64.45% of that of base metal. The main reasons are that the welding can lead to stress concentration in the flash area, tensile welding residual stress in the welded joint（ The residual stress value was 30. 5 MPa）, as well as the grain size is not uniform in the heat-affected zone. The cleavage steps or quasi-cleavage patterns present on the fatigue fracture surface, the fracture type of the FSW butt joint belongs to a brittle fracture.展开更多
In this work, the joining of aluminum to steel was conducted by ultrasound enhanced friction stir weld- ing （USE-FSW）. The power ultrasound was introduced into one of the metal sheets by an ultrasonic roll seam modu...In this work, the joining of aluminum to steel was conducted by ultrasound enhanced friction stir weld- ing （USE-FSW）. The power ultrasound was introduced into one of the metal sheets by an ultrasonic roll seam module synchronously to the FSW-process. The effect of the ultrasound on the resulting welds, their microstructure and their corrosion properties was investigated by light and scanning electron microscopy and corrosion investigations. The USE-FSW-joints showed less and smaller steel particles in the nugget zone as well as a thinner continuous intermetallic phase of FeAl3 at the interface. The nondestructive testing method of computed laminography proved the observations made by optic microscopy due to non-porous joints for both techniques. Corrosion investigations showed only low corrosion current densities and no enhanced galvanic corrosion for the EN AW-6061/DC04-hybrid joints in sodium chloride solution.展开更多
Friction stir welding （FSW） and stationary shoulder friction stir welding （SSFSW） were carried out for the butt joining of dissimilar AA2024-T3 and AA7050-T7651 aluminium alloys with thicknesses of 2 mm. A compari...Friction stir welding （FSW） and stationary shoulder friction stir welding （SSFSW） were carried out for the butt joining of dissimilar AA2024-T3 and AA7050-T7651 aluminium alloys with thicknesses of 2 mm. A comparison between the two processes was performed by varying the welding speed while keeping the rotational speed constant, Through the analysis of the force and torque produced during welding and a simple analytical model, it was possible to show that in SSFSW there is more effective coupling with the tool and the heat produced is more efficiently distributed. This process decreases both the welding area and the diffusion at the interface of the two alloys compared with FSW. The minimum microhardness occurred at the advancing side （AS） at the interface between the thermo-mechanically affected zone （TMAZ） and the stir zone （SZ） in both processes, although the decrease was more gradual in SSFSW. This interface is also where all specimens failed for both welding technologies. An increase in tensile strength was measured in SSFSW compared with standard FSW. Furthermore, it was possible to establish the mechanical performance of the material in the fracture zone using digital image correlation.展开更多
基金supported by the Program for New Century Excellent Talents from the Ministry of Education (Grant No. NCET-11-0984)
文摘An attempt has been made to improve the corrosion resistance of friction stir welded joints of 7075 aluminum alloys by micro-arc oxidation（MAO）, and the effects of Na2Si O3 concentration in electrolyte on the corrosion resistance of the coatings were discussed. Morphology and phase constituents of the MAO coatings produced in electrolyte with different Na2SiO3 concentrations were analyzed by scanning electron microscopy, confocal laser scanning microscopy and X-ray diffraction. Electrochemical tests were conducted to evaluate the corrosion resistance of the coatings. The results show that the corrosion resistance of the coated joints is much better than that without the ceramic coating, and the ceramic coating produced in the electrolyte with Na2SiO3 concentration 20 g/L showed better corrosion resistance than the others.
基金financially supported by the National Natural Science Foundation of China (No. 51105030)
文摘The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion（EXCO） solution. Electrochemical measurements（open circuit potential, potentiodynamic polarization curves, and electrochemical impedance spectroscopy）, scanning electron microscopy, and energy dispersive spectroscopy were employed for analyzing the corrosion mechanism. The results show that, compared to the base material, the corrosion resistance of the friction-stir welds is greatly improved, and the weld nugget has the highest corrosion resistance. The pitting susceptibility originates from the edge of Al-Cu-Fe-Mn-Si phase particles as the cathode compared to the matrix due to their high self-corrosion potential. No corrosion activity is observed around the θ phase（Al2Cu） after 2 h of immersion in EXCO solution.
基金supported by the National Natural Science Foundation(No.51265013)the Natural Science Foundation of Jiangxi Province(No.20151BAB206007)
文摘The fatigue properties of friction stir welded （FSW） butt joint and base metal of MB8 magnesium alloy were investigated. The comparative fatigue tests were carried out using EHF-EM2OOK2-070-IA fatigue testing machine for both FSW butt joint and base metal specimens. The fatigue fractures were observed and analyzed using a scanning electron microscope of JSM-6063LA type. The experimental results show that the fatigue performance of the FSW butt joint of MB8 magnesium alloy is sharply decreased. The conditional fatigue limit （2 x 106） of base metal and welded butt joint is about 77.44 MPa and 49. 91 MPa, respectively. The conditional fatigue limit （2 x 106 ） of the welded butt joint is 64.45% of that of base metal. The main reasons are that the welding can lead to stress concentration in the flash area, tensile welding residual stress in the welded joint（ The residual stress value was 30. 5 MPa）, as well as the grain size is not uniform in the heat-affected zone. The cleavage steps or quasi-cleavage patterns present on the fatigue fracture surface, the fracture type of the FSW butt joint belongs to a brittle fracture.
基金supported by the DFG Priority Program 1640:“Joining by plastic deformation”
文摘In this work, the joining of aluminum to steel was conducted by ultrasound enhanced friction stir weld- ing （USE-FSW）. The power ultrasound was introduced into one of the metal sheets by an ultrasonic roll seam module synchronously to the FSW-process. The effect of the ultrasound on the resulting welds, their microstructure and their corrosion properties was investigated by light and scanning electron microscopy and corrosion investigations. The USE-FSW-joints showed less and smaller steel particles in the nugget zone as well as a thinner continuous intermetallic phase of FeAl3 at the interface. The nondestructive testing method of computed laminography proved the observations made by optic microscopy due to non-porous joints for both techniques. Corrosion investigations showed only low corrosion current densities and no enhanced galvanic corrosion for the EN AW-6061/DC04-hybrid joints in sodium chloride solution.
文摘Friction stir welding （FSW） and stationary shoulder friction stir welding （SSFSW） were carried out for the butt joining of dissimilar AA2024-T3 and AA7050-T7651 aluminium alloys with thicknesses of 2 mm. A comparison between the two processes was performed by varying the welding speed while keeping the rotational speed constant, Through the analysis of the force and torque produced during welding and a simple analytical model, it was possible to show that in SSFSW there is more effective coupling with the tool and the heat produced is more efficiently distributed. This process decreases both the welding area and the diffusion at the interface of the two alloys compared with FSW. The minimum microhardness occurred at the advancing side （AS） at the interface between the thermo-mechanically affected zone （TMAZ） and the stir zone （SZ） in both processes, although the decrease was more gradual in SSFSW. This interface is also where all specimens failed for both welding technologies. An increase in tensile strength was measured in SSFSW compared with standard FSW. Furthermore, it was possible to establish the mechanical performance of the material in the fracture zone using digital image correlation.
