The microstructure, microhardness and quasi-static failure behavior of resistance spot welds of AA6111-T4 aluminum alloy were experimentally investigated. Optical metallography and high-resolution hardness traverses w...The microstructure, microhardness and quasi-static failure behavior of resistance spot welds of AA6111-T4 aluminum alloy were experimentally investigated. Optical metallography and high-resolution hardness traverses were utilized to characterize the weld nugget, heat affected zone and base metal. The AA6111 spot welds displayed a softer nugget and hardened heat affected zone, compared with the base metal. The through-thickness hardness of the base metal sheet was not constant and had to be carefully considered to determine the effect of welding on material properties. Quasi-static lap-shear tensile tests were used to determine the failure load and failure mode. All tensile specimens failed through the interfacial fracture. This failure mode is consistent with the observed reduced hardness in the weld nugget.展开更多
Friction stir spot welding technique was employed to join pure copper （C11000） and pure aluminium （AA1060） sheets. The evolving properties of the welds produced were characterized. The spot welds were produced by ...Friction stir spot welding technique was employed to join pure copper （C11000） and pure aluminium （AA1060） sheets. The evolving properties of the welds produced were characterized. The spot welds were produced by varying the rotational speed, shoulder plunge depth using different tool geometries. The presence of a copper ring of different lengths was observed on both sides of the welds indicating that Cu extruded upward into the Al sheet which contributed to obtaining strong welds. The microstructure showed the presence of copper particles in the aluminium matrix which led to the presence of various intermetallics observed by the energy dispersive spectroscopy and X-ray diffraction. The maximum tensile failure load increases with an increase in the shoulder plunge depth, except for the weld produced at 800 r/min using a conical pin and a concave shoulder. A nugget pull-out failure mode occurred in all the friction stir spot welds under the lap-shear loading conditions. High peaks of Vickers microhardness values were obtained in the vicinity of the keyhole of most of the samples which correlated to the presence of intermetallics in the stir zone of the welds.展开更多
Ti-4Al-1.5Mn dual phase titanium alloy sheet was spot welded by pneumatic resistance spot welder.The effects of different welding parameters on shear load and nugget diameter were studied.The results show that the max...Ti-4Al-1.5Mn dual phase titanium alloy sheet was spot welded by pneumatic resistance spot welder.The effects of different welding parameters on shear load and nugget diameter were studied.The results show that the maximum shear load of solder joint increases first and then decreases with the increase of electrode pressure and welding current,while the nugget diameter increases with the increase of electrode pressure and welding current.Electrode pressure of 0.20 MPa and welding current of 46 A are the optimal process parameters,under which the maximum shear load of solder joint reaches 8.80 kN.The microstructure of nugget zone is coarse acicular martensite,and the solder joints fail in a mixed mode of intergranular brittle-ductile fracture.展开更多
基金Project(0211005303101)supported by the Fundamental Research Funds for the Central Universities,ChinaInternational Cooperation Project(2014DFA51270)supported by Ministry of Science and Technology of ChinaProject(2009-5043R)supported by the Ford Motor Company University Research Program,USA
文摘The microstructure, microhardness and quasi-static failure behavior of resistance spot welds of AA6111-T4 aluminum alloy were experimentally investigated. Optical metallography and high-resolution hardness traverses were utilized to characterize the weld nugget, heat affected zone and base metal. The AA6111 spot welds displayed a softer nugget and hardened heat affected zone, compared with the base metal. The through-thickness hardness of the base metal sheet was not constant and had to be carefully considered to determine the effect of welding on material properties. Quasi-static lap-shear tensile tests were used to determine the failure load and failure mode. All tensile specimens failed through the interfacial fracture. This failure mode is consistent with the observed reduced hardness in the weld nugget.
基金financial support of the University of Johannesburg and the assistance from Mr Riaan Brown (Nelson Mandela Metropolitan University) for operating the MTS PDS I-Stir machine are acknowledged
文摘Friction stir spot welding technique was employed to join pure copper （C11000） and pure aluminium （AA1060） sheets. The evolving properties of the welds produced were characterized. The spot welds were produced by varying the rotational speed, shoulder plunge depth using different tool geometries. The presence of a copper ring of different lengths was observed on both sides of the welds indicating that Cu extruded upward into the Al sheet which contributed to obtaining strong welds. The microstructure showed the presence of copper particles in the aluminium matrix which led to the presence of various intermetallics observed by the energy dispersive spectroscopy and X-ray diffraction. The maximum tensile failure load increases with an increase in the shoulder plunge depth, except for the weld produced at 800 r/min using a conical pin and a concave shoulder. A nugget pull-out failure mode occurred in all the friction stir spot welds under the lap-shear loading conditions. High peaks of Vickers microhardness values were obtained in the vicinity of the keyhole of most of the samples which correlated to the presence of intermetallics in the stir zone of the welds.
基金supported by the Priority Academic Program Development of Jiangsu Higher Education Institution and Beijing Institute of Aeronautical Materials(No.KZ82171509)。
文摘Ti-4Al-1.5Mn dual phase titanium alloy sheet was spot welded by pneumatic resistance spot welder.The effects of different welding parameters on shear load and nugget diameter were studied.The results show that the maximum shear load of solder joint increases first and then decreases with the increase of electrode pressure and welding current,while the nugget diameter increases with the increase of electrode pressure and welding current.Electrode pressure of 0.20 MPa and welding current of 46 A are the optimal process parameters,under which the maximum shear load of solder joint reaches 8.80 kN.The microstructure of nugget zone is coarse acicular martensite,and the solder joints fail in a mixed mode of intergranular brittle-ductile fracture.
