The Relationship Between Weld Color and Welding Quality of Titanium Welding

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1. The color change and defect generation mechanism of titanium and titanium alloy titanium pipe welds

The welding seam defects of titanium and titanium alloy titanium pipes and their production mechanism are as follows. When welding titanium pipes, the argon gas maintenance layer formed by the argon arc welding gun can only protect the welding pool from the harmful effects of air, and it will not affect the solidification. The welding seam and its surrounding area in the vicinity of high temperature have no protective effect, while the titanium pipe welding seam and its adjacent area in this state still have a strong ability to absorb nitrogen and oxygen in the air. It starts to absorb oxygen at 400°C, and absorbs nitrogen from 600°C. The air contains a lot of nitrogen and oxygen.

As the oxidation level gradually increases, the color of the weld seam of the titanium pipe changes and the weld plasticity decreases. Silver-white (non-oxidized) golden yellow (TiO, titanium starts to absorb hydrogen at about 250°C. Slightly oxidized) blue (Ti2O3 oxidation is slightly severe) gray (TiO2 oxidation is severe).

2. The quality of titanium welding can be judged by the color of the surface of the titanium weld

Tested the different colors and hardness of titanium welds

1) It is proved through experiments that as the color of the weld deepens, that is, the degree of oxidation of the weld increases, the hardness of the weld increases. Through the test of the peer experiment, the hardness of the titanium metal increases, and there are such things as oxygen and nitrogen in the weld. Hazardous substances increase and greatly reduce the quality of welding.

2) The weldability of titanium has a very important relationship with its chemical and physical properties, but the key is that at high temperatures, the high activity of titanium is easily polluted by air, and when heated, its grains swell When the welded joint cools, it will form a brittle phase. The melting point of titanium is very high, which can reach 1668±10°C, which is more energy than welding steel. At the same time, titanium is more chemically active and interacts with O and H much easier than steel. It is sharper than 600°C. Compound. A large amount of H and O can be absorbed at 100°C, and the H dissolving capacity is tens of thousands of times greater than that of steel, which then generates titanium hydride, which makes the toughness drop sharply. Gas impurities increase the tendency of cold cracks and delayed cracks, increasing notch sensitivity. Therefore, the purity of argon for welding should be no less than 99.99%, the humidity should be no more than 0.039%, and the hydrogen content of the welding wire should be less than 0.002%. The heat transfer coefficient of titanium is 1/2 of that of steel. At 882℃, the transition from α to β occurs. No matter the temperature is higher, the β grains will grow up abruptly and the performance will be significantly deteriorated. Therefore, the temperature must be strictly controlled, especially the welding The high temperature residence time in the thermal cycle. There are no hot cracks and intergranular cracks when welding titanium, but there are porosity problems, especially when welding α+β alloys.

Based on the above research, the following issues should be paid attention to when welding titanium metal:

① During the titanium welding process, the welding area and the high temperature area after welding should be strictly protected to avoid air entering the welding and high temperature area which will seriously affect the quality of the weld. necessary.

② The weld groove is required to be processed by machining (no polishing method is allowed for processing);

③ Spot welding should be avoided, and high-frequency arc starting should be used.

④ Avoid post-weld heat treatment; if post-weld heat treatment is necessary, the heat treatment temperature should be less than 650℃.

The quality control of titanium welding has a very important influence on the weld color of titanium welding. At the same time, the quality of titanium welding can also be judged according to the weld color of titanium welding. There is a very important relationship between the two.

Shanghai Geheng Vacuum Technology Co., Ltd. is a vacuum heat treatment furnace manufacturer with many years of experience in design, manufacturing and production. Mainly produce vacuum heat treatment furnace, vacuum sintering furnace, vacuum brazing furnace, New Energy And Environmental Protection Equipment and other vacuum equipments.Provide customized services, equipment work area can be based on customer output.