| With the aggravation of the world energy crisis and the continuous development ofautomobile industry,the lightweight of automobile body has become one of the trends in the development of automobile industry.the development of aluminum-steel integrated body structure is an effective way to realize it.Cause the physical and chemical properties of aluminum and steel are significantly different,brittle and hard intermetallic compounds are easily formed at the interface during spot welding,which restricts the research and application of aluminum-steel integrated body.Therefore,it is of great value to study the resistance spot welding of dissimilar metals in aluminum and steel and to explore the methods to improve the welding quality.In this paper,the shape and size of F-type electrode are improved,and the optimized electrodes are made.the optimized electrodes size are as follows: the upper electrode is convex electrode,the height of convex plate is 1 mm,and the diameter of convex plate is 6mm;The lower electrode is a concave electrode with an outer diameter of 12 mm,an inner diameter of 8 mm,and a concave depth of 0.8 mm.Resistance spot welding of 5083 aluminum alloy with 1.0 mm thickness and galvanized steel with 1.0 mm thickness was carried out by using intermediate frequency inverter resistance welder.The macro-morphology,microstructure and mechanical behavior of dissimilar metal spot welding joints under optimized electrode were discussed,including fracture mode,common defects,electrode loss and its influence.The results show that the spot welding joint of aluminum and steel is essentially a fusion-brazing joint.There are two forms of fracture mode in tensile test:interfacial fracture and drawing fracture.The welding process is often accompanied by cracks,shrinkage and welding spatter defects;The surface of the optimized electrode is easy to collapse and adhere to the aluminum plate,which will have a great influence on the surface morphology and nugget position of the joint.When F-type electrode is used,the test results show that the spot welding joint with high tensile strength can be obtained under the parameters of welding current 8k A,welding time130 ms and electrode pressure 150 kg,and the tensile strength can reach 2984 N.The influence of welding parameters under the optimized electrode on microstructure and mechanical properties of spot welding joint was studied.The test results show that with theincrease of welding current,welding time and electrode pressure,the tensile strength of the joint increases first and then decreases.When the welding current was 12 k A,welding time was 200 ms and electrode pressure was 250 kg,the spot welding joint with the highest tensile strength was obtained.at this time,the nugget depth of the joint was 0.45 mm,and the tensile strength was 4579 N.compared with the optimal welding joint under F-type electrode,the tensile strength was increased by 53 %,and the indentation rate was significantly reduced.It is proved that the comprehensive properties of the spot-welded joints can be significantly improved by using the optimized electrode for dissimilar metal resistance spot welding of aluminum and steel.In order to study the influence of welding parameters on joint strength under F-type electrode and optimized electrode,variance analysis and artificial neural network based on genetic algorithm were used to analyze and process the test data.The results show that in the selected welding parameters interval,the order of significance of parameters under F-type electrode is welding current > electrode pressure > welding time,while under optimized electrode is welding current > welding time > electrode pressure.The interaction between welding current and welding time has a significant effect on joint strength.The strength prediction figure obtained by the artificial neural network model is consistent with the test results. |
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