Research On Microstructures And Mechanical Properties Of TIG Arc Welding-brazing Joints For TC4 Titanium/2A12 Aluminium Alloys

Considering the requirement for light-weight and low-cost designing in modern industry,the welding of titanium alloy with superior mechanical properties and aluminium alloy with light-weight and low-cost can effectively lower the workpieces weight,and meet the demand of light-weight design for structures,green and sustainable development.It is quite difficult to obtain the high-grade dissimilar joints of titanium and aluminum alloys due to the great differences in physical,chemical properties between the two alloys.As a kind of technique of welding-brazing,TIG arc welding-brazing has great advantages in the practical operation,in which the joining is obtained in one side through welding between the filler and alloys with lower melting-temperature,and the joining is realized in another side via brazing between the filler and the alloys with higher melting-temperature at the same time.Thus TIG arc welding-brazing is applicable in the dissimilar welding and joining with high quality and high efficiency under various working conditions.As a result,the researches about TIG arc welding-brazing of titanium and aluminum alloys are full of theoretical significances,practical industrial manufacturing and the engineering application values.Based on these backgrounds,the TIG arc welding-brazing of TC4 titanium and 2A12 aluminium alloys was achieved with three kinds of fillers,including 5A06(the Al-Mg series),A380(the Al-Si-Cu series)and 4047(the Al-Si series).We studied the microstructure characteristics,mechanical properties and fracture behaviors of the joints,and we also analyzed the effect of fillers' compositions on microstructure,intermetallic compounds layer and mechanical properties of the joints.It was found that the TIG arc welding-brazing of TC4/2A12 could be obtained by these three fillers.The welded joints filled with different fillers have differences in the microstructural morphologies,grain sizes and the distribution of second phases due to the differences of fillers compositions.The high Si content in 4047 fillers effectively prevented the diffusion of Ti element to the seam,owing to the effect of Si on preventing the formation of intermetallic compounds.The intermetallic-compound layer in the brazing interface of joint filled by the 4047 filler was in the structure of serration and homogeneous in thickness,which was much thinner than the intermetallic-compounds layers in the joints filled by the 5A06 and A380 fillers.No Ti-Al intermetallic compounds were detected in the joints filled by the 4047 filler.Compared with the joints filled with 5A06 fillers,the addition of Si and Cu elements in fillers could improve the mechanical properties of joints effectively,of which the ultimate tensile strength of joints filled with A380 fillers reached 135 MPa and the ultimate tensile strength of joints filled by the 4047 filler was the best,which reached 225 MPa.The joints filled with 5A06 and A380 fillers fractured along the intermetallic compounds layers in the interfaces between Ti base metal and seams,due to the stress concentration induced by the intermetallic compounds layers in the bottom interfaces of Ti base metal.The intermetallic compound layers in the interfaces filled with 4047 fillers was homogeneous and the thickness was about 1-6 ?m,thus the joints fractured at the seam with the characteristics of ductile fracture owing to the low content of stress concentration.Overall,the mechanical properties of joints filled with the 4047 fillers were relatively best under the current processing parameters of TIG arc welding-brazing procedure.