Microstructure And Mechanical Properties Of AC CMT Coupled With High-frequency Pulse Current Welded Al-Li Alloys

Al-Li alloys,as low density and high-performance material for aerospace equipment,were welded using AC CMT coupled with high-frequency pulse current.The influences of stirring action of high-frequency pulse current on the porosity,joints softening of welded joints were investigated.AC CMT was coupled with high-frequency pulse current by the way of parallel connection,the morphology of composite arc and arc voltage and current signals when the pulse frequency was 50KHz were acquired by“High-speed cameras and electrical synchronous acquisition and analysis system”;different base metal and filler wires were selected to analysis the influence of high-frequency pulse current on welded joints.First,1420 Al-Li alloy was used as base metal and ER4043 welding wire was selected as filling metal,the frequency of pulse current was respectively 20KHz,30KHz,40KHz,50KHz,60KHz,70KHz,80KHz,the frequency range which had a significant impact on the quality of welding was selected by analyzing the microstructure and mechanical properties of welded joints;then 2060 and 2198 Al-Li alloys were welded by selected ER4043 as filling metal,high-frequency pulse current was coupled to verify the consistency of welding different base materials;then another kind of welded wire ER5356 was selected,the frequencies having a significant impact on the quality of welded joints was coupled to the AC CMT,the consistency of using different filling materials was tested based on the comprehensive performance of welded joints.The experimental observations showed that the size and distribution of porosity in the welded joints show obvious decreasing trend with the frequency of 50KH_Z and 60KH_Z regardless of which filler wires(ER4043 or ER5356)or base materials(1420,2198 and2060 Al-Li alloys),and the grain refinement was evidence.The mechanical properties increased with different frequency and most significant with the frequencies of 60KH_Z and70KH_Z.The hardness of the welded joint has been significantly improved,the tensile strength increased by about 6%when the sheets were welded when the frequencies of the pulse current were 60KHz or 70KHz also.Through the comprehensive analysis,the quality of welding have a significant improve when the range of high-frequency pulse current is mainly in 50KHz~70KHz.This study has significance impact on porosity reducing,grain refinement,reducing the degree of softening and improving the welding quality of Al-Li alloys.