| Titanium/steel laminated composite plate has the advantages of these two kinds of metal materials,reducing the use of titanium or titanium alloy and the cost,which is widely used in aerospace,nuclear power plant,petrochemical,marine engineering and other fields.But the welding technology of titanium/steel laminated composite thin plate(0.5 ~ 4mm)is not mature,which greatly limits its application now.In this paper,the 2mm cool rolled TA2 commercial pure titanium(TA2)/409 stainless steel(409SS)laminated composite plate was used to research the effect of three kinds of laser welding technology(TA2 surface,409 SS surface,and 409 SS surface and adding Cu foil are the three variables)on the welding quality,macroscopic morphology,microstructure and mechanical properties of the welded joints under different laser welding conditions.The main conclusions are as follow:(1)When the TA2 surface was irradiated by laser,the cross section morphology of all welded joint was “funnel-shaped”,and all fractured after welding.Which showed that the welding performance of the composite plate was very poor under the condition.The welded joints with free crack and small pores were obtained by controlling the appropriate heat input under the two conditions(409SS surface and adding Cu-foil),which shown that the welding performance of the composite plate was greatly improved.With the increase of heat input,the morphology of the welded joints was changed from “funnel-shape” to “hourglass-shape”.(2)When TA2 surface was irradiated by laser,because of the large proportion of Ti in the molten pool,the main microstructure of the welded joints was Ti Fe2,including small amount of Ti Fe,Ti7Fe35Cr13 and Fe-Cr SS.These Ti-Fe intermetallic compounds and the thermal stress seriously deteriorated the mechanical properties of the welded joints.When the laser irradiated the 409 SS surface,due to the “funnel effect”,under the small heat input conditions,the microstructure was mainly Fe-Cr SS,only including a very small amount of Ti Fe2,and the formation of intermetallic compounds was restrained to a certain extent.However,with the increase of heat input,Ti-Fe intermetallic compounds gradually increase,and there was local aggregation phenomenon,resulting in local small cracks.The formation of Ti-Fe intermetallic compounds of the welded joints with Cu-foil was further suppressed under the small heat input conditions.The microstructure was mainly Fe-Cr SS and Cu SS.With the increase of heat input,the content of Cu SS gradually decreased,and the content of Ti Fe2 increased.(3)The microhardness of the heat affected zone of the three kinds of welded joints has little difference,the microhardness of the 409 SS side heat affected zone was 180 ~ 260 HV,and the microhardness of the TA2 side heat affected zone was 350 ~ 600 HV.The average microhardness of the weld area of the TA2 joint was 985 HV,and the maximum microhardness of the measured point was 1147 HV.When the 409 SS surface was irradiated by laser,the minimum mean microhardness of the welded zone of the joints was 310 HV,while the minimum average microhardness of the weld zone with Cu foil was further reduced and the value was 290 HV.The average micro hardness of the two kinds of the welded joints increased with the increase of the heat input.(4)The fracture location of three kinds of welded joints were all at the weld zone,and the fracture was brittle fracture,and the elongation of which was obviously lower than that of the substrate,and the value was not more than 5 %.When the laser irradiated TA2 surface,the welded joint fractured spontaneously after welding,the tensile strength is zero.When the laser irradiated 409 SS surface,the maximum tensile strength of the welded joint was 408 MPa,about 77.6 % of the subsrate.When the Cu foil was added,the maximum tensile strength of the welded joint was 465 MPa,about 88.6 % of the base material.By comparing and analyzing the experimental conclusions of laser butt welding of TA2/409 SS laminated composite plate under different welding conditions,409 SS welding surface,adding Cu foil and controlling small heat input are three key factors to obtain the welded joints with good welding quality and mechanical properties. |
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