Research On Automatic Low Heat Input Welding Process And Joint Quality Of 5A06 Aluminum Alloy Sheet

In order to solve the problems of the various weld forms,low welding efficiency and difficult to achieve welding automation of 5A06 aluminum alloy thin-walled fuel tank,this topic introduced the newly developed low-heat input automatic melting electrode welding technology,focused on CMT,AC-CMT,P-MIG,CMT+P and compared these four high-efficiency and low-heat input welding processes.The differences in welding process,forming characteristics,microstructure,mechanical properties and pore tendency of butt welds under similar heat input conditions were studied respectively,and the suitable process for the automatic welding of 5A06 aluminum alloy thin-walled special fuel tank robots is obtained.First,the plate surfacing method was used to study the weld formation under the four process conditions.In the AC-CMT process,the influence of the EP/EN ratio on the weld formation was studied,and it is found that when the ratio of EP/EN is 13:7,19:1 or 25:1,the weld surface is well formed;then the influence of the wire feeding speed and arc length correction coefficient on the weld formation of the four processes of AC-CMT,CMT,P-MIG,and CMT+P was studied,and the best process parameter ranges for butt welding of the four processes were determined.Under the AC-CMT process,the wire feeding speed is between8.2m/min～8.5m/min,under the CMT process,the wire feeding speed is about 5.6m/min,and under the P-MIG process,the wire feeding speed is about 5.3m/min,the wire feeding speed under CMT+P process is between 5.0m/min～5.3m/min.The arc length correction coefficient for the four processes is between 0%and 15%.Then carried out the butt welding test study to compare the microstructure and mechanical properties of the joints under the four processes.The results showed that the mirostructure of the weld zone under the four processes isα（Al）+β（Al₈Mg₅）,the grain size of the weld zone under AC-CMT and CMT processes is small,81.04μm and 87.12μm,respectively.The grain size of the weld zone under the P-MIG and CMT+P process is larger,129.28μm and 147.42μm,respectively;from the base material to the weld zone,the Mg element content fluctuates significantly in the weld zone,and the content decreases.Among them,the Mg element content decreases the most under the CMT+P process;the tensile strength and elongation after fracture of the welded joint under the P-MIG process are the largest.The tensile strength is 318MPa,which is 89.1%of the base material,and the elongation is 14.6%.The tensile strength and elongation of the joint under the CMT process are the lowest.The tensile strength is 286MPa,which is 80.1%of the base material,and the elongation is 11%.The fracture modes are ductile fracture;the joint bending performance under the AC-CMT and P-MIG processes is good,and when the bending angle is 180°,no cracks appear on the joint surface.Finally,the porosity distribution of the welded joint was analyzed.The porosity of the weld is the lowest under the P-MIG process,which is 0.09%,and the porosity of the weld under the CMT process is the highest,which is 1.28%;in the P-MIG process,as the welding speed increases,the porosity of the weld first decreases and then increases.When the welding speed is 11mm/s and 12mm/s,the porosity of the weld is low,which is 0.09%and 0.21%,respectively.Combining the mechanical properties of welded joints under the four processes and the characteristics of weld pore distribution,among the four processes,the P-MIG process has the lowest weld porosity and good joint bending performance,which is more suitable for automatic welding of aluminum alloy thin-walled special fuel tank by robot.