Titanium alloys are widely used in aerospace, medical equipment and other industries due to their advantages such as high specific strength and thermal conductivity, good corrosion resistance and biocompatibility. Due to the particularity of dissimilar metal connection, common methods include diffusion welding, friction stir welding, fusion brazing, laser welding, cold pressure welding and other special connection techniques. 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 its application range.
Titanium alloy/steel dissimilar welding composite structure not only has 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 large difference in thermal conductivity and linear expansion coefficient between titanium alloy and steel, and poor mutual solubility, brittle and hard Ti-Fe intermetallic compounds are easily formed during welding, making it difficult to weld dissimilar titanium alloy/steel . In order to solve these problems, the researchers conducted in-depth research and analysis on the diffusion welding, brazing, explosive welding and other welding technologies of titanium alloy/steel dissimilar metals.
Ti6Al2Zr2Mo2V titanium alloy and 304 austenitic stainless steel were electron beam welded, and the filler material used was a V/Cu-based composite material. Experiments show that a single filler cannot effectively inhibit the formation of Ti Fe intermetallic compounds, and only two or more fillers can achieve the inhibition effect. Lihang Titanium has used Ti+Zr-based 40Ti-20Zr-20Cu-20Ni solder, silver-based Ag-6Pd solder, nickel-based BNi2 and BNi7 solder to braze Ti-6Al-4V titanium alloy and STS304 stainless steel. Welding experiment. Experiments show that Ni in the Ni-based filling material can effectively act as a stabilizing element, thereby reducing the transition temperature of the β phase. For Ag-based filler materials, although other materials can be added to increase the strength of the welded joint, the poor affinity of Ag and Ti cannot effectively improve the diffusion of the filler material. Wetting angle and the number of atoms diffused into the steel side base material BNi7≥BNi2>40>Ag-5Pd. The microstructure of the explosive welding joint zone of titanium and 20 steel was analyzed. The steel side and the titanium side base metal at the welding interface contained high-density dislocations. Among them, the steel side appeared equiaxed fine crystals and deformation. Long grain area. A composite interface fused with each other can be observed in the bonding zone, indicating that the high energy generated by the explosion melts the interface metal, and the spraying and quenching of liquid metal causes the appearance of microcrystals, micro twins and metastable phases of titanium in the bonding zone. Using pure Ag as a filler material for pressure diffusion welding of industrial pure titanium and 304 stainless steel, experiments show that Ag can effectively inhibit the formation of brittle intermetallic compound Ti-Fe, and the intermetallic compound formed by Ag has a strong bearing capacity, thereby improving welding The strength of the joint.
Dissimilar metal welding refers to the joining of two different types and properties of metal materials through a specific welding process to form a structural member with integrity and expected performance. The thermal conductivity and linear expansion coefficient of titanium alloy and dissimilar metals are quite different, and brittle intermetallic compounds are easily formed during the welding process, which leads to the deterioration of the strength of the welded joint. Therefore, it is very necessary to add appropriate intermediate transition metal, select appropriate welding process and welding method in the welding process to improve the microstructure and mechanical properties of the welded joint.
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