Study On Microstructure And Properties Of Titanium Alloy And Aluminum Alloy Laser Lap Welded Joints Using High-entropy Alloy Fillers

In order to combine the excellent properties of titanium alloys and aluminum alloys,the research on titanium alloy/aluminum alloy composite structures has received more and more attention.It has many applications in automobile production,aerospace,weapons manufacturing,rail transportation and other fields.It is precisely because titanium alloys and aluminum alloys have the advantages of low density,corrosion resistance,and good mechanical properties that they have a wide range of use scenarios.However,the thermophysical properties of titanium alloy and aluminum alloy are quite different,and the mutual solubility of the two in each other is also very poor,which causes it is easy to form intermetallic compounds.Most of the intermetallic compounds generated by titanium alloy and aluminum alloy are brittle phases,which increases the difficulty of welding between the two and severely restricts the application scope of titanium alloy/aluminum alloy composite structures in actual production and life.Therefore,breaking through the limitations of metallurgical incompatibility when welding titanium alloys and aluminum alloys,reducing the number of Ti-Al intermetallic compounds,and greatly improving the mechanical properties of joints are the main research directions of titanium alloy/aluminum alloy welding.In this paper,high-entropy alloys(HEA)are used as filler metals to realize laser welding of titanium alloy/aluminum alloy lap joints.The technological feasibility of different types of high-entropy alloy filler materials applied to titanium alloy/aluminum alloy laser welding was studied.At the same time,the effects of laser welding parameters on the microstructure and properties of HEA joints were also studied.CoFeNiTi_1.2Mn_0.8(BCC type),CoNiCu_1.25Nb_0.5V_1.25(FCC type),SnMnNiCuNb_0.5V_1.5(FCC+BCC type)three different types of high-entropy alloy filling materials are applied to titanium alloy/aluminum process feasibility in the field of alloy laser welding was studied.The results show that CoFeNiTi_1.2Mn_0.8(BCC type) high-entropy alloy is brittle,and a large number of cracks appear in the joint under the action of welding stress,which is not suitable for laser welding of titanium alloy/aluminum alloy dissimilar metals.When laser welding titanium alloy/aluminum alloy by lap joint,the aluminum alloy plate should be used as the lower plate and the titanium alloy plate should be used as the upper plate and beveled.When the laser is incident at an angle of 45 degrees,adjusting the laser process parameters can realize Effective connection of titanium alloy/aluminum alloy;the study found that when using CoNiCu_1.25Nb_0.5V_1.25(FCC type)filler material,the spot diameter is between1.5-3mm,the laser power is between 600-660w,and the welding speed is between 9Defect-free welded joints can be obtained at-10.5mm/s.When SnMnNiCuNb_0.5V_1.5(FCC+BCC type)high-entropy alloy powder is used as the filling material,the spot diameter and welding speed remain unchanged,and defect-free welded joints can be obtained when the laser power is between 520-580w.Based on the summary of the applicable range of each parameter in the welding process,under the condition of a fixed spot diameter of 1.8mm,the titanium alloy/aluminum alloy with CoNiCu_1.25Nb_0.5V_1.25(FCC type)high entropy alloy filling material under different parameters was studied.The characteristics of forming,microstructure and mechanical properties of alloy laser welded joints reveal the influence of welding parameters on joint forming,microstructure and mechanical properties.It was found that the CoNiCu_1.25Nb_0.5V_1.25(FCC type)high-entropy alloy filler can prevent the titanium alloy and the aluminum alloy base metal from mixing and reacting under appropriate parameters.Under the experimental conditions,the maximum tensile strength of the joint reaches 200MPa.Based on the summary of the applicable range of various parameters in the welding process and the research on the joints with CoNiCu_1.25Nb_0.5V_1.25(FCC type)high-entropy alloy filler materials,the FCC+BCC type SnMnNiCuNb_0.5V_1.5high-entropy alloy was used as the the filler material was used to weld titanium alloy and aluminum alloy.The influence of different laser parameters on joint forming,microstructure and mechanical properties was analyzed,and the relationship between joint forming,microstructure and mechanical properties was studied.The experimental results showed that the addition of tin reduces the melting point of the high-entropy system and increases the fluidity of the high-entropy alloy;the maximum tensile strength of the joint is 230MPa,and the mechanical properties are improved;when the welding heat input is too large,the aluminum Ti-Al intermetallic compounds were detected on the alloy side.Although Ti-Al intermetallic compounds were detected in the joint with the increase of heat input,the effect of preventing the base metal from mixing and reacting was still obvious.The formation of Ti-Al intermetallic compounds was not detected,and only a small amount was distributed near the Al-side base metal interface.