Why do dentation pores appear on the surface of GMAW welds?
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. Why do dented pores appear on the surface of welds made with cored wire? Answer: Since flux-cored wire is a tubular wire made by winding thin steel strips, it belongs to seamed wire ； Moisture in the air can penetrate into the flux core through gaps, causing the flux to become damp (unable to be dried), which results in indentations and pores in the weld seam. 2. Why are there technical requirements for the purity of CO2 gas? Answer: Generally, CO2 gas is a by-product of chemical manufacturing, with a purity of only around 99.6%, containing trace amounts of impurities and moisture, which can cause defects such as pores in the welds. When welding important products, it is essential to use CO2 gas with a purity of ≥99.8%, as this results in fewer weld pores, a lower hydrogen content, and improved crack resistance. 3. Why do MAG welded joints have higher impact toughness than CO2 welded joints? Answer: During MAG welding, the active gas makes up only 20%; the alloying elements in the wire have a high transition coefficient, resulting in high impact toughness of the weld. The active gas for CO2 welding is 100%; manganese and silicon, which are alloying elements in the wire, work together to remove oxygen. The transition coefficient of these alloying elements is slightly lower, resulting in weld impact toughness that is not as high as that of MAG welding. For example, the Tangshan Shinko MG-51T welding wire (equivalent to ER50-6) has the following impact toughness value at room temperature: MAG: 160J ； CO2: 110J.
4. What is flux-cored wire? Answer: It is a type of welding wire made by rolling thin steel strips into circular steel tubes and then filling them with powder of a specific composition, followed by drawing. 5. Why is CO2 gas used for shielding flux-cored wires? Answer: Based on the protection method, flux-cored wires are divided into two types: flux-cored gas-shielded welding wires and flux-cored self-shielded welding wires. Flux-cored gas shielded welding wires generally use CO2 gas for protection, belonging to the combined gas-slag shielding method; they yield welds with good shape and high overall mechanical properties. 6. Why do dentation pores appear on the surface of wire rod welds? Answer: Since flux-cored wire is a tubular wire made by winding thin steel strips, it belongs to seamed wire ； Moisture in the air can penetrate into the flux core through gaps, causing the flux to become damp (unable to be dried), which results in indentations and pores in the weld seam.
7. Why are there technical requirements for the purity of CO2 gas? Answer: Generally, CO2 gas is a by-product of chemical manufacturing, with a purity of only around 99.6%; it contains trace amounts of impurities and moisture, which can cause defects such as pores in the welds. When welding important products, it is essential to use gas with a CO2 purity of ≥99.8% – this results in fewer weld pores, a lower hydrogen content, and improved crack resistance. 8. Why are there high technical requirements for argon purity? Answer: There are currently three types of argon available on the market: regular argon (with a purity of around 99.6%), pure argon (with a purity of around 99.9%), and high-purity argon (with a purity of 99.99%). The first two types can be used for welding carbon steel and stainless steel ； When welding non-ferrous metals such as aluminum and aluminum alloys, as well as titanium and titanium alloys, high-purity argon must be used ； Prevent the welds and heat-affected zones from oxidizing, which could prevent welding. 9. Why are there various sizes of TIG welding nozzles? Answer: There are 4–8 different sizes of nozzles available. For welding carbon steel, nozzles of size 4–5 can be used, while for welding stainless steel, aluminum, and aluminum alloys, larger nozzles of size 6–7 should be employed to enhance the coverage of protection around the weld seam and the heat-affected zone. When welding non-ferrous metals such as titanium and titanium alloys, a nozzle with a size of 7–8# or larger should be used to prevent oxidation of the weld seam and heat-affected zone.
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