Titanium alloys are widely used in aerospace, medical equipment and other industries because of their advantages such as high specific strength and thermal conductivity, good corrosion resistance, and good biocompatibility. Due to the particularity of the dissimilar metals connection, the commonly used methods are diffusion welding, friction stir welding, fusion brazing, laser welding, cold pressure welding and other special connection technologies. Studying the welding of titanium alloys and dissimilar metals is an effective way to give full play to the excellent properties of titanium alloys and expand their application range.
Titanium alloy / steel dissimilar welding composite structure not only has the high specific strength and good corrosion resistance of titanium alloy, but also is compatible with the advantages of wide application range and low price of steel materials. However, due to the great difference between the thermal conductivity and linear expansion coefficient of titanium alloy and steel, and the poor mutual solubility, brittle and hard Ti-Fe intermetallic compounds are easily generated during welding, making it difficult to dissimilar titanium alloy / steel . In order to solve these problems, the researchers have conducted in-depth research and analysis on the diffusion welding, brazing, explosive welding and other welding technologies related to titanium alloy / steel dissimilar metals.
Ti6Al2Zr2Mo2V titanium alloy and 304 austenitic stainless steel were electron beam welded, and the filler material used was V / Cu-based composite material. Experiments show that a single filler can not effectively inhibit the formation of Ti Fe intermetallic compounds, only two or more fillers can achieve the inhibitory effect. Lihang Titanium Industry used Ti + Zr-based 40Ti-20Zr-20Cu-20Ni solder, silver-based Ag-6Pd solder, nickel-based BNi2 and BNi7 solders to braze Ti-6Al-4V titanium alloy and STS304 stainless steel Welding experiment. Experiments show that Ni in Ni-based fillers can effectively act as a stabilizing element, thereby reducing the transition temperature of β phase. For Ag-based filler materials, although the addition of other materials can improve the strength of the welded joint, due to the poor affinity of Ag and Ti, the diffusion of the filler material cannot be effectively improved. Wetting angle and the number of atoms diffused into the base metal of the steel side BNi7≥BNi2> 40> Ag-5Pd. The microstructure of the titanium and 20 steel explosive welding joint area was analyzed. The steel side and the titanium side base material at the welding interface contain high-density dislocations. Among them, equiaxed fine grains and deformation pulling appear on the steel side Long grain area. A composite interface fused with each other can be observed in the bonding area, indicating that the high energy generated by the explosion melts the interface metal, and the spraying and quenching of the liquid metal cause the occurrence of microcrystals, micro twins and titanium metastable phases in the bonding area. Using pure Ag as a filler material for pressure diffusion welding of industrial pure titanium and 304 stainless steel, the experiment shows that Ag can effectively inhibit the formation of brittle intermetallic compounds Ti-Fe, and the intermetallic compounds formed by Ag have a strong bearing capacity, thereby improving welding The strength of the joint.
Heterogeneous metal welding refers to connecting two different kinds of metal materials with different properties through a specific welding process and forming structural parts with integrity and expected performance. Titanium alloys and dissimilar metals have large differences in thermal conductivity and linear expansion coefficient, and brittle intermetallic compounds are easily formed during the welding process, resulting in poor welded joint strength. Therefore, it is very necessary to add appropriate intermediate transition metal and select appropriate welding process and welding method to improve the microstructure and mechanical properties of the welded joint during the welding process.
