| The sea will become a fierce international competition place in twenty-first Century and in the future.China is vigorously developing marine resources.Titanium alloys are widely used in marine equipment engineering because of their high specific strength,workability and good corrosion resistance.However,when titanium and its alloys are used as welded structures,the effect of welding thermal cycle will reduce the mechanical properties of joints and cause electrochemical corrosion easily.There are many reports on the mechanical properties of titanium alloys at home and abroad,but there are few reports on the microstructure and properties of the welded joints and their corrosion resistance in the special environment of the ocean atmosphere.Therefore,this topic applies TIG welding to 2mm thick TC4 thin plate,and studies the welding joint of different welding parameters to the welding joint of TC4 titanium alloy.The influence of the mechanical properties of the head and the influence of the welding current on the microstructure characteristics of the welded joint,the mathematical model of the relationship between the grain size and the welding current is established,and the microstructure of the coarse grain zone in the heat affected zone of the welded joint is obtained by the thermal simulation technology;and the neutral salt fog test and the salt fog ultraviolet cycle test are used.The influence of corrosion time on the corrosion behavior of parent metal,coarse grain zone and weld metal was studied in simulating atmospheric and marine environment.The study shows that the tensile strength of welding joint is 1080 MPa when the welding current I=80A and welding speed V=14m/h,higher than that of the parent material,the elongation is 12.72%,it is 56% of the parent material,and the welding joint has the best comprehensive performance under the welding parameters.The TC4 welding joint is thecolumnar crystal area of the weld,the coarse grain zone in the heat affected zone and the heat influence.The grain size of the TC4 welded joint has a nonlinear change from the heat affected zone to the parent material,and decreases with the increase of the distance between the weld center and the weld center.The grain size changes at the junction of the weld zone and the heat affected zone,and the maximum grain size changes at the abrupt change.There is a linear relationship between the welding current and the welding current,and a large number of martensitic martensite is formed in the tissue obtained by the thermal simulation technology,which is basically consistent with the microstructure characteristics of the coarse grain region in the heat affected zone obtained from the actual welding.The electrochemical test shows that the self corrosion potential of the parent material,the coarse grain area and the weld in the original sample decreases in turn,the self corrosion current increases in turn and the resistance arc decreases in turn.It shows that the corrosion resistance of the parent material is the best,the corrosion resistance of the weld is the worst,the corrosion resistance of the coarse grain region is the second,and the three of the base material,the coarse grain area and the weld seam are accompanied by the corrosion.After 60 days corrosion,the corrosion resistance of the weld is the worst,which indicates that the weld is still the weak area of the welded joint.The corrosion weightlessness test of the three regions found that the weight loss is unknown and the titanium alloy is very good under the atmosphere ocean.The corrosion resistance of the weld samples of 60 days after the salt spray corrosion is corroded with oxygen in the air to produce the corrosion products mainly of oxygen,titanium and chlorine,indicating that the TC4 titanium alloy TIG joint will be corroded in the ocean atmosphere. |
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