TC4 titanium alloy is a metal with very active chemical properties. It has a strong affinity for gases such as hydrogen, oxygen and nitrogen at high temperatures. Titanium has strong chemical reactions with O, N, CO2, water vapor and nitrogen in the atmosphere. reaction.
When the carbon content is greater than 0.2%, hard TiC is formed in the titanium alloy. When the temperature is high, it reacts with N to form a TiN hard surface layer. At temperatures above 600°C, titanium can absorb oxygen to form a hardened layer with higher hardness. Titanium alloy absorbs gas and produces a hard and brittle surface layer with a depth of up to (0.1~0.15) mm, and the degree of hardening is (20~30)% higher than the original matrix hardness.
Especially during the welding process, this ability becomes more intense as the temperature increases. Practice has proved that if the absorption and dissolution of titanium alloy and hydrogen, oxygen, nitrogen and other gases are not controlled during welding, it will undoubtedly cause problems for titanium alloy welding. The welding process of joints brings great difficulties. In order to master the welding process of titanium alloys and improve the welding quality, we must have an in-depth understanding of the characteristics of titanium and titanium alloys.
Experiments have proven that when welding titanium alloys, the heat input, interlayer temperature, protective gas purity, flow rate, structural form and size of the nozzle and the distance from the weldment, joint form and internal and external gas protection devices meet the requirements, indoor and outdoor or wind strength , Mechanical cleaning and degreasing of the welding wire base material will affect the welding quality. Therefore, when welding titanium alloys, attention should be paid to the rationality of various protective measures and whether the preparations are in place, etc., which play a key role in the welding quality of titanium alloys.
