Welding and Testing of Titanium Alloy Materials
As temperature rises, the ability of titanium and its alloys to absorb hydrogen, oxygen and nitrogen increases. Titanium begins to absorb hydrogen from 250 ° C, oxygen begins at 400 ° C, and nitrogen starts to vaporize from 600 ° C. Due to the high affinity of the titanium alloy with O2, N2, H2, the inclusion of these gases in the joint will make the joint brittle and reduce the impact performance, ductility and toughness of the titanium alloy welded joint. When hydrogen is reflected in the titanium alloy, delayed cracking occurs in the heat-affected zone. When the weld contains oxygen and nitrogen, the weld or heat-affected zone will also crack under the action of larger welding stress, and the crack also belongs to the delayed cracking. Therefore inert gas (or vacuum chamber) protection is very necessary. Due to the high cost of using a vacuum chamber, inert gas protection is typically used. The main shielding gas helium and argon, the helium price higher than argon, in general, not the unique requirements of titanium alloy welded joints and heat-affected zone, the use of high-purity argon to protect the oxidation can be prevented.
Most titanium alloys can be welded using oxyacetylene welding and all titanium alloys can be soldered using solid state welding methods such as TIG, MIG, plasma arc welding, laser and electron beam welding. In fact, titanium alloy welded joints tend to crack less than black metal such as ferrous and nickel alloys. Although titanium alloys have such useful properties and some other excellent welding characteristics, some engineers still think that the welding of titanium alloys is quite difficult. The foremost reason is that the welding of titanium alloys requires extremely high gas protection. Generally, only the professional staff ensure gas protection meets the requirements. In fact, various welding methods can be used to weld titanium alloys. Owing to the introduction of air during the welding of N2, O2 and carbon materials make the titanium alloy melt welded brittle, so to be welded area must be clean and use inert gas protection. Welding materials are basically based on the characteristics of the material to be determined. The weldability of titanium alloys is generally assessed on the basis of the ductility and strength of the welded joints.
Current trends in laser welding of titanium alloys are becoming more widespread. Laser welding has less deformation, higher production efficiency and is more automated than e-beam and TIG. Compared with electron beam welding, laser welding does not prescribe complex equipment such as vacuum chamber, so laser welding more practical, and laser welding can be directly welded in different welding conditions. CO2 laser due to large power, the use of 25kW / h can be a one-time penetration of 20mm thick titanium plate. Nd: YAG lasers make YAG welding more flexible due to the energy transfer that can be made using optical fibers, but the depth of penetration is limited due to the low power. Laser welding prone to splash, so that the surface is not clean, cannot be carried out in the welding process must be especially careful.
Post-weld inspection: Visual inspection of the welded parts of titanium alloys is mainly to assess the quality of gas protection. When the surface was silver white, said the gas protection is very good; and when the surface is light yellow or dark yellow, titanium alloy was slightly contaminated, but still acceptable; the surface is dark blue, said the pollution is more serious, but due to the use of The condition is different, some can be used; the surface is light blue, serious pollution, almost impossible to use; the surface is gray blue or gray, the pollution is very serious, can not be used; the same surface is white, the pollution is very serious, unavailable.
Color test methods: hardness testing and eddy current testing can be used to detect whether the joints contain impurities, due to the nature of the joints will contain impurities, mainly in the presence of impurities when the dual hardness and resistivity will be significantly higher. Portable hand-held hardness tester can be tested in situ weldment hardness. The application of this technology can easily detect the quality of the welding quality. Under normal circumstances, there are less welding cracks in the titanium case. However, cracks sometimes occur in the weld or due to impurities. At this point, defects can be discovered by coloring examination, at the same time this method also has some effect on the loose. It must be pointed out that before proceeding with the welding, the coloring solution must be cleaned.
As temperature rises, the ability of titanium and its alloys to absorb hydrogen, oxygen and nitrogen increases. Titanium begins to absorb hydrogen from 250 ° C, oxygen begins at 400 ° C, and nitrogen starts to vaporize from 600 ° C. Due to the high affinity of the titanium alloy with O2, N2, H2, the inclusion of these gases in the joint will make the joint brittle and reduce the impact performance, ductility and toughness of the titanium alloy welded joint. When hydrogen is reflected in the titanium alloy, delayed cracking occurs in the heat-affected zone. When the weld contains oxygen and nitrogen, the weld or heat-affected zone will also crack under the action of larger welding stress, and the crack also belongs to the delayed cracking. Therefore inert gas (or vacuum chamber) protection is very necessary. Due to the high cost of using a vacuum chamber, inert gas protection is typically used. The main shielding gas helium and argon, the helium price higher than argon, in general, not the unique requirements of titanium alloy welded joints and heat-affected zone, the use of high-purity argon to protect the oxidation can be prevented.
Most titanium alloys can be welded using oxyacetylene welding and all titanium alloys can be soldered using solid state welding methods such as TIG, MIG, plasma arc welding, laser and electron beam welding. In fact, titanium alloy welded joints tend to crack less than black metal such as ferrous and nickel alloys. Although titanium alloys have such useful properties and some other excellent welding characteristics, some engineers still think that the welding of titanium alloys is quite difficult. The foremost reason is that the welding of titanium alloys requires extremely high gas protection. Generally, only the professional staff ensure gas protection meets the requirements. In fact, various welding methods can be used to weld titanium alloys. Owing to the introduction of air during the welding of N2, O2 and carbon materials make the titanium alloy melt welded brittle, so to be welded area must be clean and use inert gas protection. Welding materials are basically based on the characteristics of the material to be determined. The weldability of titanium alloys is generally assessed on the basis of the ductility and strength of the welded joints.
Current trends in laser welding of titanium alloys are becoming more widespread. Laser welding has less deformation, higher production efficiency and is more automated than e-beam and TIG. Compared with electron beam welding, laser welding does not prescribe complex equipment such as vacuum chamber, so laser welding more practical, and laser welding can be directly welded in different welding conditions. CO2 laser due to large power, the use of 25kW / h can be a one-time penetration of 20mm thick titanium plate. Nd: YAG lasers make YAG welding more flexible due to the energy transfer that can be made using optical fibers, but the depth of penetration is limited due to the low power. Laser welding prone to splash, so that the surface is not clean, cannot be carried out in the welding process must be especially careful.
Post-weld inspection: Visual inspection of the welded parts of titanium alloys is mainly to assess the quality of gas protection. When the surface was silver white, said the gas protection is very good; and when the surface is light yellow or dark yellow, titanium alloy was slightly contaminated, but still acceptable; the surface is dark blue, said the pollution is more serious, but due to the use of The condition is different, some can be used; the surface is light blue, serious pollution, almost impossible to use; the surface is gray blue or gray, the pollution is very serious, can not be used; the same surface is white, the pollution is very serious, unavailable.
Color test methods: hardness testing and eddy current testing can be used to detect whether the joints contain impurities, due to the nature of the joints will contain impurities, mainly in the presence of impurities when the dual hardness and resistivity will be significantly higher. Portable hand-held hardness tester can be tested in situ weldment hardness. The application of this technology can easily detect the quality of the welding quality. Under normal circumstances, there are less welding cracks in the titanium case. However, cracks sometimes occur in the weld or due to impurities. At this point, defects can be discovered by coloring examination, at the same time this method also has some effect on the loose. It must be pointed out that before proceeding with the welding, the coloring solution must be cleaned.
