Titanium And Copper Dissimilar Metals Welded Joint By Cold Metal Transfer And Corrosion Behavior

Titanium and titanium alloys have low density, remarkable strength, good plasticity and toughness, good fatigue performance, adequate corrosion resistance, high temperature strength, good biocompatibility and high specific strength, are excellent lightweight structural materials. Copper and copper alloys have excellent electric and thermal conductivity, good cold and hot working performance, high oxidation resistance and corrosion performance of fresh water, salt water, ammonia alkali solution and organic chemical. Some copper alloys also have high strength. The effective joint of titanium alloys and copper alloys will meet some special structural parts of weight loss and other performance requirements, and present the performance advantages of titanium alloy and copper alloy, and make the best use of titanium alloy and copper alloy. The effective joint of titanium and copper not only meets the requirements of light weight and high strength, but also satisfies the demand for electrical conduction, heat conduction, corrosion resistance and wear resistance. Then this joint may have a broad application prospect in the aerospace, instrument, shipbuilding, chemical engineering fields, etc.Cold metal transfer welding technology is a new type arc welding process with digital coordinate method of wire feeding speed and droplet transfer process. Cold metal transfer welding technology has many characteristics which are different from other welding heat source for its unique energy transfer and conversion mechanism, and has unique advantage in the field of dissimilar materials welding. Therefore, titanium alloy and copper alloy dissimilar metals welding by cold metal transfer method was carried out. The stability of the arc welding process and weld appearance were investigated. The macroscopic and microscopic microstructures of the welded joint were analyzed. The connection mechanisms of titanium and copper dissimilar metals were illuminated. The correlations of welding process parameters, microstructures and mechanical properties were discussed. Finally, corrosion behavior of titanium and copper dissimilar metals welded joint were researched and analyzed.The experimental results showed that:For the lap joint of top Cu (T2) sheet bottom Ti (TA2and TC4) sheet, the satisfied welded joints with smooth surface and good shape could be obtained with wire feeding speed of4.5-5.0m/min and wire deviated distance of1mm. The wire and Cu sheet were molten and mixed to form the Cu side interface zone. Moreover, the liquid filler metal wetted and spread on the little molten or maintain solid Ti sheet to form the Ti side interface zone. The joint had the tensile shear strength of200N/mm, and fractured in the heat affected zone (HAZ) of Cu. For the lap joint of top Ti (TA2and TC4) sheet-bottom Cu (T2) sheet, the satisfied welded joints with smooth surface and good shape could be obtained with wire feeding speed of6.0-6.5m/min and wire deviated distance of0mm. The wire and Cu sheet were molten and mixed to form the Cu side interface zone. Moreover, the liquid filler metal wetted and spread around the partial molten Ti sheet to form three interface zones at Ti side. With increasing of the connection area of the weld metal and Ti (TA2and TC4), the strength of the welded joint was greatly improved. The Ti-Cu lapped joint had tensile shear strength of190N/mm, and fractured in the HAZ of Cu. For the butt joint of1mm thick Ti (TA2and TC4) sheet and1mm thick Cu (T2) sheet, the satisfied welded joints with smooth surface and good shapes could be obtained with wire feeding speed of4.5-5.0m/min and wire deviated distance of1-2mm. The wire and Cu sheet were molten and mixed to form the Cu side interface zone. Moreover, the liquid filler metal wetted and spread around the little molten or maintain solid Ti sheet to form three interface zones at Ti side. The1mm thick Ti lmm thick Cu butt joint has the tensile strength of200MPa, and fractured in the HAZ of Cu. For the butt joint of3mm thick Ti (TA2) sheet and3mm thick Cu (T2) sheet, the little effects of groove angle on the mechanical properties of the joint was produced. The satisfied welded joints with smooth surface and good shape could be obtained with appropriate wire feeding speed. The wire and Cu sheet were molten and mixed to form the Cu side interface zone. Moreover, the liquid filler metal wetted and spread around the little molten or maintain solid Ti sheet to form Ti side interface zone. The3mm thick Ti-3mm thick Cu butt joint has the tensile strength of200MPa, and fractured in the HAZ of Cu. The Cu side interface zone of Ti/Cu dissimilar metal welded joint were similar, part of Cu base metal was molten and mixed with filler metal. In solidification, the solidified molten metal was nucleated on the fusion line between weld metal and Cu base metal and grew up quickly in cylindrical-like style. Weld metal zone were composed of α-Cu solid solutions and Cu-Al-Ti-Fe-Ni multi-phases. But, weld metal zone consisted of a small amount of V element for TC4Ti alloy. The Ti interface zone mainly consisted of Ti2Cu, TiCu, AlCu2Ti and α-Cu solid solutions orderly from the Ti base metal to the weld metal. The thickness of the intermetallic compounds layer was un-uniformed. The Ti interface zone near the Ti (TC4) base metal side had a certain amount of TiAl intermetallic compound for TC4Ti alloy. Cu crystal particles grow rapidly in HAZ due to heat cycle, which made tensile shear strength of the joints decrease, and induced the specimens fracture in the Cu HAZ with plastic fracture mode. There were corrosion grooves in Ti interface zones after corrosion for7days, and self-fracture after corrosion for14days. SEM-EDS analysis results showed that the intermetallic compounds layer in Ti side interface zone were corroded.