Research On High-frequency Pulse Coupled Square Wave AC-TIG Welding Of 6061-T6 Aluminum Alloy

AC-TIG welding is one of the main welding process for aluminum alloys material.However,it suffers from low welding penetration and productivity.Moreover,TIG welded aluminum joints are susceptible to weld defects such as porosity,hot crack and HAZ softening.In order to solve these problems,High frequency pulse ac TIG welding technology has been paid more and more attention.The application of the high-frequency pulse coupled TIG welding method is limited by the welding power source.Therefore,the new welding process in this paper is based on the conventional square wave ac TIG welding,and the high-frequency pulse square wave current with pulse frequency greater than 10kHz is parallel at both ends of the arc.TIG welding technology was studied:in this paper.First,based on the 6061-T6 aluminum alloy plate with thickness of 6mm,a series of orthogonal tests of TIG welding without wire filling were carried out.The influence of high frequency pulse parameters on arc shape was analyzed.The effect of the high-frequency pulse frequency,the current matching relation of square wave ac current and high-frequency pulse peak current,and the high-frequency pulse duty ratio on weld formation and microstructure properties were investigated respectively.In the welding process,the self-developed "image-electrical parameter synchronous acquisition system" is used to acquis the welding current,arc voltage and arc shape of the welding process in real time,the macroscopic defects and microstructure morphology of the cross section of the welding bead were analyzed after welding.Experimental results show that compared with conventional ac TIG welding,the arc profile was more concentrated,and the stability and stiffness were improved.Weld porosity decreased significantly.By greatly optimizing the welding process parameters,the optimal welding process parameters of 6061-T6 aluminum alloy plate with thickness of 6mm were obtained respectively as follows.The high frequency pulse frequency is 30kHz～40kHz,the high frequency pulse peak current is 80A-105A,and the duty ratio of high frequency pulse is 50%.Within the optimal welding parameter range,the arc width shrinks by about 10%and the weld penetration increases by more than 90%,the porosity can be reduced by 82%,the grain size of weld can be refined by 37.21%.In addition,compared with conventional ac TIG welding process,high-frequency pulse-assisted TIG welding process can save at least equivalent current of 20A under the condition of equal penetration.The welding parameters of the optimal welding process parameter interval were selected to conduct a direct butt welding test for the 6061-T6 aluminum alloy plate with a thickness of 6mm plate.The flow of weld pool in welding process was analyzed by high-speed camera,the strength and tensile strength of butt joint were compared and analyzed,and the macrostructure and microstructure of cross section of butt joint were analyzed.By comparing with conventional ac TIG welding process.the flow in the molten pool of high frequency pulse-assisted TIG welding process was more stable,the thermal crack tendency was smaller,the joint structure distribution was more uniform,the grain in the weld zone was more refined,the thermal influence zone was reduced,and the plastic toughness and strength of the joint were improved obviously.Experimental results show that,compared with conventional ac TIG welding,high-frequency pulse current can increase the strength,hardness and plasticity of welded joints(heat affected zone)by 8.5%,22.6%and 19.8%respectively,and the strength,hardness and plasticity of welded joints(weld zone)by 6.1%,22.7%and 50.8%respectively.The results show that high frequency pulse current assisted square wave TIG welding has the advantages of convenient parameter adjustment,good joint quality and high welding efficiency.