Cracks and pores in the welding joints of titanium plates and titanium rods

During the welding process of titanium plates and rods, we often encounter problems such as cracks in the welding joints and pores in the weld seams.

1. Pores in the weld seam
Pores are a common problem. The fundamental cause of pores is the influence of hydrogen. The formation of pores in the weld metal mainly affects the fatigue strength of the joint. The main technical measures to prevent the occurrence of pores include: 1. Maintain the purity of the argon gas, which should be no less than 99.99% when welding titanium and titanium alloys. 2. Completely remove organic substances such as oxide scale and oil from the weldment surface and the surface of the welding wire. 3. Apply good gas maintenance to the molten pool, control the flow rate and velocity of argon gas well to prevent turbulent flow and affect the maintenance effect. 4. Select the welding process parameters correctly, increase the residence time of the deep pool to utilize the escape of bubbles, which can effectively reduce pores.

2. Cracks in the welding joint
The possibility of thermal cracks in the welding joint is very small. When welding titanium and titanium alloys, this is because the content of SPC and other impurities in titanium and titanium alloys is very low. The low melting point eutectic formed by SP is not likely to appear on the grain boundaries. In addition, the effective crystallization temperature range is narrow, and the shrinkage of titanium and titanium alloys during solidification is small, so the weld metal will not form thermal cracks. When welding titanium and titanium alloys, cold cracks may occur in the heat affected zone. Its characteristic is that the crack occurs several hours or even longer after welding, which is called delayed crack. Research has shown that this crack is related to the diffusion of hydrogen during the welding process. During the welding process, hydrogen diffuses from the high-temperature deep pool to the lower-temperature heat affected zone. The increase in hydrogen content causes an increase in the amount of TiH₂ precipitated in this area, increasing the brittleness of the heat affected zone. In addition, the volume expansion caused by the precipitation of hydrogen compounds leads to large microstructural stress, and the diffusion and accumulation of hydrogen atoms to this high-stress area result in the formation of cracks. The main method to prevent this delayed crack is to reduce the source of hydrogen in the welding joint. Generally, vacuum annealing treatment can be carried out.