Main applications of titanium alloy materials such as TC4 titanium rod and TA1 titanium rod in aviation industry

When welding titanium and titanium alloys, the possibility of hot cracks in the welded joint is very small. This is because the content of impurities such as S, P, and C in titanium and titanium alloys is small, and the low melting point eutectic formed by S and P is not easy to appear in On the grain boundary, in addition to the narrow effective crystallization temperature range, the shrinkage of titanium and titanium alloys is small during solidification, and the weld metal will not produce thermal cracks. However, when welding titanium and titanium alloys, cold cracks may appear in the heat-affected zone, which is characterized by cracks that occur several hours or even longer after welding and are called delayed cracks. During the welding process, hydrogen diffuses from the high-temperature deep pool to the lower-temperature heat-affected zone. The increase in hydrogen content increases the amount of TiH2 precipitated in this zone, which increases the brittleness of the heat-affected zone. In addition, the volume expansion during the precipitation of hydrides causes larger structural stress. In addition, hydrogen atoms diffuse and accumulate to the high-stress parts of the region, resulting in the formation of cracks.

Porosity is a common problem encountered in titanium rod processing and welding of titanium and titanium alloys. The root cause of the formation of pores is the result of the influence of hydrogen. The formation of pores in the weld metal mainly affects the fatigue strength of the joint. Hydrogen is the main cause of cold cracks and pores. Because hydrogen is less than 300, the solubility in α phase is very small, and the limit solubility is only 0.002% at room temperature. When the weld or heat-affected zone cools below 300 after welding, supersaturated hydrogen is precipitated in the form of titanium hydride (γ phase). The volume increases and produces intergranular stress, and the development of this stress will cause intergranular microcracks. The intergranular microcracks will expand into cracks under the action of external stress.

When welding titanium alloy, when the temperature is higher than 500~700, it is easy to absorb oxygen, hydrogen and nitrogen in the air, which seriously affects the welding quality. Therefore, when welding titanium alloys, the entire molten pool and the weld area of ​​the high temperature part (above 400~650) must be strictly protected. For this reason, special protective measures must be taken when welding titanium and titanium alloys. Therefore, the method of argon arc welding is used, and a larger welding torch is used to enlarge the area of ​​the gas protection zone. When the nozzle is not enough to protect the weld and the high temperature metal near the seam, it is necessary to supplement the argon protective drag cover.
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