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

(1) Experimental evidence shows that as the color of the weld seam darkens, indicating an increase in the degree of weld seam oxidation, the hardness of the weld seam also increases. Through tests by peers, it is found that the hardness of titanium metal increases, and harmful substances such as oxygen and nitrogen in the weld seam also increase, significantly reducing the quality of the welding.

(2) The weldability of titanium is closely related to its chemical and physical properties. However, the key point is that at high temperatures, titanium's high reactivity makes it prone to air contamination. During heating, its grains expand, and when the welded joint cools, it forms brittle phases. Titanium has a very high melting point, reaching 1668 ± 10°C, which requires more energy than welding steel. Moreover, titanium is chemically very active and reacts with O and H much more easily than steel, especially above 600°C when the reaction intensifies. At 100°C, it absorbs a large amount of H and O, with its hydrogen absorption capacity being tens of thousands of times greater than that of steel, thereby generating titanium hydride and sharply reducing its toughness. Gas impurities increase the tendency of cold cracking and delayed cracking, as well as notch sensitivity. Therefore, the purity of argon used for welding should be no less than 99.99%, and the humidity should not exceed 0.039%. The hydrogen content of the welding wire should be below 0.002%. The heat transfer coefficient of titanium is half that of steel. At 882°C, it undergoes an α to β transformation. If the temperature is higher, the β grains grow rapidly and in a leapfrog manner, significantly deteriorating its performance. Therefore, the temperature must be strictly controlled, especially the high-temperature dwell time during the welding thermal cycle. When welding titanium, there are no issues of hot cracking or intergranular cracking, but there is a problem of porosity, especially when welding α+β alloys.