Welding porosity refers to the gas holes formed in the weld metal, which can reduce the strength and quality of the weld and even lead to leakage or breakage. Therefore, it is very important to understand the causes and solutions of welding porosity to improve welding technology and ensure welding quality.
There are various reasons for welding porosity, mainly in the following aspects:
The influence of welding materials. If there are impurities such as oil, rust, oxide scale on the surface of the welding wire, electrode, flux or base metal, or if the chemical composition of the welding wire and the base metal does not match, it will cause a large amount of gas to be generated during the welding process, resulting in the formation of pores. Therefore, it is necessary to select the appropriate welding materials before welding, and clean and dry them.
Effect of shielding gas. If the purity of the shielding gas is not enough, or the flow rate is unstable, or it is disturbed by the wind, it will destroy the effective protection of the arc and the molten pool, so that the oxygen and nitrogen in the air will enter the molten pool, thus forming pores. Therefore, it is necessary to choose the appropriate shielding gas when welding, and control the flow and pressure, and at the same time take windproof measures.
The impact of the welding process. If the welding current, voltage, arc length, welding speed, welding torch angle and other parameters are not selected properly, or the welding operation is not standardized, it will affect the stability of the arc and the fluidity of the molten pool, resulting in the gas cannot be discharged in time, thus forming pores. Therefore, when welding, it is necessary to select reasonable welding process parameters according to different welding methods and welding objects, and weld in accordance with the standardized operation methods.
The effects of the welding environment. If the temperature, humidity, air pressure and other factors of the welding environment change greatly, or the groove shape, gap, positioning and other factors of the welding part are unreasonable, it will affect the cooling rate and shrinkage deformation of the molten pool, resulting in the change of gas solubility, thus forming pores. Therefore, it is necessary to choose a stable welding environment as much as possible when welding, and carry out reasonable design and assembly of the welding part.
Based on the different reasons for the occurrence of welding porosity, the solutions to welding porosity are mainly as follows:
Preheating and post-heat treatment are used. Preheating can reduce the temperature gradient of the welded part, reduce the solubility of the gas, and promote the discharge of the gas. Post-heat treatment can eliminate the residual stress of the weld, improve the structure and properties of the weld, and eliminate or reduce the influence of porosity. The temperature and time of preheating and post-heat treatment should be selected and controlled according to different welding materials and welding methods.
Welded with reactive gas or pulsed laser. Reactive gases can chemically react with gases in the molten pool to produce compounds that are easy to discharge, thereby reducing the formation of pores. Pulsed laser welding can change the behavior of the pores by reducing the amount of shielding gas being entrapped in the pores, thereby reducing or eliminating porosity.
Beam swing or arc swing is employed. Beam oscillation or arc oscillation can increase the fluidity of the weld pool, facilitate the discharge of gases, and improve the forming and filling of welds, thereby reducing or eliminating porosity.
Repair or re-weld is employed. If porosity has already formed in the weld, repair or rewelding can be used to eliminate or reduce porosity. Repair refers to re-soldering at the porosity, filling the wire or flux so that the porosity disappears or becomes smaller. Rewelding refers to re-welding on the entire weld so that the original weld is completely melted and re-solidified, so that the porosity disappears or becomes smaller. When repairing or rewelding, it is necessary to pay attention to the selection of appropriate welding materials and welding processes to avoid the creation of new porosity or other defects.
In conclusion, welding porosity is a common welding defect, which can affect welding quality and welding performance, and even lead to welding failure. Therefore, in order to effectively prevent and solve welding porosity, it is necessary to start from many aspects, comprehensively consider welding materials, shielding gas, welding process, welding environment and other factors, and take reasonable measures to improve the level of welding technology and ensure welding quality.