Research On The Microstructure And Properties Of 2195 Aluminum-lithium Alloy Laser-MIG Hybrid Welding

The target to lightweight in the aviation field can be achieved by the light-weighting of the material and the integrity of structure.Al-Li alloy has a broad application prospect in the aviation field due to the light weight and high performance.However,the difficulty of welding Al-Li alloy is an important factor restricting its further application.In this work,the 3mm thick 2195 Al-Li alloy was processed by laser MIG hybrid welding,A stereo microscope was employed to characterize the macroscopic morphology of the weld.The microstructure and phase composition of the welded joint were determined by metallographic microscope(OM),scanning electron microscope(SEM)and energy dispersive spectroscopy(EDS).X-ray diffraction(XRD)was utilized to analyze the phase composition of weld and BM.The mechanical properties of welded joints were measured by micro-hardness tester and hydraulic servo universal testing machine.Electrochemical corrosion performance of welded joints was evaluated by a electrochemical integrated test system.The inter-granular corrosion test was conducted to analyze the inter-granular corrosion performance of welded joints.The research results obtained are as follows:The parameters of the welding process affect the formation of the weld,With the increase in the laser power from 700W to 1000W,the stability of welding is improved,as well as spatter defects reduction,The width of the upper weld increased,but the width of the lower part did not change much.The melting area increased from 26.18 mm2 to 33.58mm2,and when the laser power 1300W,the weld defect appeared on the back of weld.The upper weld width decreased a little,and the lower weld width increased obviously.Melting area dropped to 30.74 mm2;When the welding speed increases from 11.5mm/s to 14mm/s and 16.5mm/s,the upper width and melting area of the weld decrease gradually,but the width of the lower part does not change obviously.The melting area also decreased from 33.58 mm2 to 25.22 mm2 and 21.79 mm2,respectively with the increase of welding speed.When the laser power reaches 1300W,welding bead defects can be found on the back of the weld.When the laser power is 1000W and welding speed is 14mm/s,the best weld forming quality is obtained.The incomplete penetration defect occurs when the welding speed is 19mm/s.The microstructure of the weld center is equiaxed crystal and isometric dendrites,which of the edges of the weld are columnar dendrites and cell crystals.The main precipitation phase of the weld is-(AlLiSi)phase and ?-(Al2Cu)phase.The laser power increases with increasing the heat input,as well as the microstructure of the weld to be coarsened,the precipitation phase decreases,which tends to be unevenly distributed.As the welding speed increases,the microstructure of the weld becomes refined with the precipitation phase evenly distributed increasing.Welding process parameters affect the formation of equiaxed fine grained regions(EQZ)by changing the flow of molten metal near the weld line.Micro-hardness analysis of welded joints shows that,the BM has the highest micro-hardness of approximately 171 HV while the Weld has the lowest.The micro-hardness of the heat affected zone fluctuates between 120 HV and 124 HV.The average micro-hardness of the weld decreases with increasing the laser power.When the laser power is up to 1300W,the micro-hardness of 108.9HV is the lowest.The micro-hardness increases first and then stabilizes with the welding speed increasing,which reaches a maximum of 119.2HV as the welding speed is 14mm/s.When the tensile test is performed,the welded joints are broken at the weld.When the laser power is 1000W and the welding speed is 14mm/s,the formation of weld bead is better and the weld phase is fine and uniform,no obvious defects such as pores can be observed,and the smallest EQZ width is obtained,so the tensile strength achieved is up to 366 MPa.Weld electrochemical corrosion test shows that,With the change of laser power and welding speed,the polarization curves are similar,and the changes of self-corrosion potential and self-corrosion current are not obvious.In the overall inter-granular corrosion test of welded joints,the inter-granular corrosion of the BM and the weld is relatively serious while that of the heat affected zone is light.Single inter-granular corrosion test in the weld zone indicates that,the average and maximum depth of inter-granular corrosion decrease with increasing the laser power but increase with increasing the welding speed.when the laser power is up to 1300W,the average and maximum depth of inter-granular corrosion is 146 ?m and 164?m,respectively.The weld shows the best inter-granular corrosion resistance.