Main Defects And Repair Methods For Welding Titanium Alloy Materials Such As Titanium Rods And Flanges

(1) titanium and titanium alloy welding, the possibility of thermal cracking of welded joints is very small, this is because titanium and titanium alloys in the S, P, C and other impurities in the content of very little, by S, P formed by the formation of low melting point of the eutectic is not easy to appear in the grain boundaries, coupled with a narrow range of effective crystallization temperature interval, titanium and titanium alloys solidified shrinkage is small, the weld metal will not produce thermal cracking. However, titanium and titanium alloy welding, the heat-affected zone may appear cold cracking, which is characterized by cracking in the hours after welding or even longer called delayed cracking. Welding process hydrogen from the high temperature deep pool to the lower temperature of the heat-affected zone diffusion, hydrogen content increases the amount of precipitation of TiH2 increased in the region, increasing the brittleness of the heat-affected zone, in addition to the precipitation due to the volume expansion of hydride caused by the greater organizational stress, coupled with the hydrogen atoms to the region of the high-stress parts of the diffusion and aggregation, resulting in the formation of cracks.

(2) titanium and titanium alloy welding, porosity is often encountered problems. The fundamental reason for the formation of porosity is due to the results of hydrogen influence. The formation of porosity in the weld metal mainly affects the fatigue strength of the joint. Hydrogen is the main cause of cold cracks and porosity formation. Because hydrogen in less than 300 ℃, in the α-phase solubility is very small, in the room temperature limit solubility of only 0.002%. When the weld or heat-affected zone in the weld cooled to 300 ℃ below, oversaturated hydrogen that is titanium hydride (γ phase) form precipitation. Volume increase and produce intergranular stress, the development of this stress will cause intergranular microcracking. Intergranular microcracks will expand into cracks under external stress.

Determination of repair method

Titanium alloy welding, when the temperature is higher than 500 ~ 700 ℃, it is easy to absorb oxygen, hydrogen and nitrogen in the air, seriously affecting the welding quality. Therefore, titanium alloy welding, the molten pool and high-temperature parts (400 ~ 650 ℃ above) of the weld zone must be strictly protected. For this reason, titanium and titanium alloy welding must take special protective measures. Therefore, the use of argon arc welding method to deal with, and the use of spray size larger welding torque, in order to expand the gas protection area, when the nozzle is not enough to protect the weld and near the seam area of high temperature metal, need to supplement the argon protection mop.

Welding preparation and bevel selection

(1) welding pieces and wire surface quality of the mechanical properties of welded joints have a great impact. Welding can be done before the test piece and wire pickling. Rinse with clean water, dry immediately after welding. Acetone, ethanol, carbon tetrachloride, methanol, etc. to wipe the titanium plate bevel and its sides (respectively, within 50 mm), the wire surface, the part of the tool holder in contact with the titanium plate.

(2) Selection of welding equipment. Titanium and titanium alloy argon arc welding should be selected with a decline in the external characteristics, high-frequency arc DC argon arc welding power supply, and delayed gas delivery time of not less than 15 s, to avoid welding suffered oxidation, pollution. So the use of WSM-315 type IGBT inverter DC pulse tig welding machine.

(3) the choice of welding materials. Argon purity should be not less than 99.99%, dew point below -40 ℃, relative humidity less than 5%. When the pressure in the argon bottle drops to 0.981 MPa, should stop using. Filler wire is generally used homogeneous materials, in order to improve the joint plasticity, can be used than the degree of alloying the base material slightly lower than the welding wire TC3, the welding wire: TC3.

(4) the choice of bevel form. In principle, to minimize the number of layers and welding metal. With the increase in the number of layers of welding, the cumulative amount of gas absorption in the weld increased to affect the performance of welded joints. And because of titanium and titanium alloy welding weld pool size is large, so the weldment open single V-type 70 ~ 80 ° bevel.

Correctly select the welding process parameters thoroughly remove the surface of the weldment, wire surface of the oxide skin, oil and other organic matter. Control the flow of argon gas and flow rate, to prevent turbulence, affecting the effect of inflatable protection. The use of manual tungsten argon arc welding titanium alloy welding cracking approach is feasible, you can get satisfactory results.