Release time：2022-11-29Click：890
The selection of aluminum and aluminum alloy welding wires is mainly based on the type of base metal, and the requirements for joint crack resistance, mechanical properties and corrosion resistance are comprehensively considered. Sometimes, when a certain item becomes a major contradiction, the welding wire selection should focus on solving this major contradiction, taking into account other requirements.
Generally, welding wires with the same or similar brand as the base metal are used to weld aluminum and aluminum alloys, so that better corrosion resistance can be obtained; However, when welding heat treatment strengthened aluminum alloy with large hot cracking tendency, the welding wire is mainly selected to solve the crack resistance problem. At this time, the composition of the welding wire is very different from the base metal.
Common defects (welding problems) and preventive measures
1. Burn through
Causes: a. Excessive heat input; b. Improper groove processing and excessive assembly clearance of weldment; c. When spot welding, the distance between welding points is too large, resulting in large deformation during welding.Preventive measures: a. Properly reduce welding current and arc voltage to improve welding speed; b. Large size of blunt edge, reduce root clearance; c. The space between welding points shall be reduced appropriately during spot welding.
2. Blowhole
Causes: a. There is oil, rust, dirt and scale on the base metal or welding wire; b. Large air flow in the welding site is not conducive to gas protection; c. The welding arc is too long, reducing the effect of gas protection; d. If the distance between the nozzle and the workpiece is too large, the gas protection effect will be reduced;
e. Improper selection of welding parameters; f. Porosity occurs at the repeated arc striking position; G. The purity of shielding gas is low and the gas protection effect is poor; h. The ambient air humidity is high.
Prevention measures: a. Before welding, carefully clean the oil, dirt, rust, scale and oxide film on the surface of welding wire and weldment, and use welding wire with high deoxidizer; b. Reasonable selection of welding site; c. Reduce the arc length appropriately; d. Keep a reasonable distance between the nozzle and the weldment; e. Select thicker welding wire as far as possible, and increase the thickness of the blunt edge of the workpiece groove. On the one hand, it is allowed to use large current. On the other hand, WeChat official account: Welding King also reduces the proportion of welding wire in the weld metal, which is effective for reducing porosity; F. Try not to strike the arc repeatedly at the same position, and grind or scrape the arc striking position when it is necessary to do so; Once the arc of a weld is started, the weld should be as long as possible, and the arc should not be broken at will to reduce the number of joints. There should be a certain weld overlap area at the joint; g. Change the shielding gas; h. Check the air flow; i. Preheat the base metal; j. Check whether there is air leakage and air pipe damage; k. Welding when the air humidity is low, or use a heating system.
3. Unstable arc
Cause: power cord connection, dirt or wind.
Preventive measures: a. Check all conductive parts and keep the surface clean; b. Remove the dirt at the connector; c. Try not to weld in the place that can cause turbulence of air flow.
4. Poor weld formation
Causes: a. Improper selection of welding specifications; b. The angle of welding torch is incorrect; c. Welders are not skilled in operation; d. The aperture of the contact tip is too large; e. The welding wire, weldment and shielding gas contain water.
Preventive measures: a. Repeated commissioning and selection of appropriate welding specifications; b. Keep proper welding torch inclination; c. Select the appropriate diameter of the conductive nozzle; d. Before welding, carefully clean the welding wire and weldment to ensure the purity of the gas.
5. Incomplete penetration
Causes: a. The welding speed is too fast and the arc is too long; b. Improper groove processing and too small equipment clearance; c. Welding specification is too small; D. The welding current is unstable.
Preventive measures: a. Properly slow down the welding speed and depress the arc; b. Reduce the blunt edge or increase the root gap appropriately; c. Increase welding current and arc voltage to ensure sufficient heat input energy of base metal; d. The addition of regulated power supply device e and fine welding wire is helpful to improve the penetration, while the coarse welding wire should be selected as appropriate to increase the deposition amount.
6. Unfused
Causes: a. The oxide film or rust on the welding part is not removed; b. Insufficient heat input.
Preventive measures: a. Clean the surface of the place to be welded before welding b. Increase the welding current and arc voltage and reduce the welding speed; c. U-shaped joints are used for thick plates, but V-shaped joints are not generally used.
7. Crack
Causes: a. Unreasonable structure design, too concentrated weld joints, resulting in excessive restraint stress of welded joints; b. The molten pool is too large, overheated, and the alloy elements are burnt out too much; c. The crater at the weld end cools quickly; d. The composition of welding wire does not match the base metal; e. The depth width ratio of the weld is too large.
Prevention measures:
a. Properly design the welding structure, reasonably arrange the welds, avoid the stress concentration zone as much as possible, and reasonably select the welding sequence; B. Reduce welding current or increase welding speed appropriately; c. The arc extinguishing operation shall be correct, and the arc striking plate shall be added or the current attenuation device shall be used to fill the arc crater; d. Welding wire shall be selected correctly.
8. Slag inclusion
Causes: a. Incomplete cleaning before welding; b. Excessive welding current causes local melting of the conductive nozzle and mixing into the molten pool to form slag inclusion; c. The welding speed is too fast.
Prevention measures: a. Strengthen the cleaning before welding. When multiple passes are welded, weld cleaning shall also be carried out after each pass is welded; b. Under the condition of ensuring the penetration, the welding current shall be reduced appropriately, and the contact tip shall not be too low during high current welding; c. The welding speed shall be appropriately reduced, and the welding wire with higher deoxidizer shall be used to increase the arc voltage.
9. Undercut
Causes: a. Too high welding current and welding voltage; b. Too fast welding speed and too little wire filling; C. The welding gun swings unevenly.
Preventive measures: a. Properly adjust welding current and arc voltage; b. Increase wire feeding speed or reduce welding speed appropriately; c. The welding gun shall swing evenly.
10. Weld contamination
Causes: a. Improper protective gas coverage; b. Welding wire is dirty; c. The base metal is dirty.
Prevention measures: a. Check whether the air supply hose leaks, whether there is air suction, whether the air nozzle is loose, and whether the protective gas is used correctly; B. Whether welding materials are stored correctly; c. Remove oil and grease before using other machinery for cleaning; d. Remove the oxide before using the stainless steel brush.
11. Poor wire feeding
Cause: A. The contact tip and welding wire are on fire; b. Welding wire wear; c. Arc spraying; d. The wire feeding hose is too long or tight; e. Improper or worn wire feed wheel; f. There are many burrs, scratches, dust and dirt on the surface of welding materials.
Prevention measures:
a. Reduce the tension of wire feeding wheel and use slow start system; b. Check the contact surface of all welding wires and minimize the metal to metal contact surface; c. Check the condition of the contact nozzle and the wire feeding hose, and check the condition of the wire feeding wheel; d. Check whether the diameter of the contact tip matches; e. Wear resistant materials shall be used to avoid cutting during wire feeding; f. Check the wear condition of welding wire disc; g. Select the appropriate size, shape and surface condition of the wire feed wheel; h. Select welding materials with good surface quality.
12. Poor arcing
Causes: a. Poor grounding; b. The size of the contact tip is incorrect; c. No shielding gas.
Prevention measures: a. Check whether all grounding conditions are in good condition, and use slow start or hot arcing mode to facilitate arcing; b. Check whether the inner space of the contact nozzle is blocked by metal materials; C. Use gas pre cleaning function; d. Change welding parameters.
Source: Welding technology
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