7 Types of Defects and Preventive Measures in Aluminum Alloy Welding

1. Welding porosity

During welding, the pores formed by the residual bubbles in the molten pool that fail to escape during solidification.

Reasons:

1) The surface of the base material or welding wire material is contaminated with oil, the oxide film is not cleaned thoroughly, or welding is not carried out in a timely manner after cleaning.

2) The purity of the protective gas is not high enough, and the protective effect is poor.

3) The gas supply system is not dry or leaking air or water.

4) Improper selection of welding process parameters.

5) Poor gas protection during the welding process and excessive welding speed.

Preventive measures:

1) Thoroughly clean the weld area and welding wire before welding.

2) Qualified protective gas should be used, and the purity should meet the specifications.

3) The gas supply system should be kept dry to prevent air and water leakage.

4) The selection of welding process parameters should be reasonable.

5) Pay attention to maintaining the accurate position between the welding torch, welding wire, and workpiece, and the welding torch should be as perpendicular to the workpiece as possible;

Try to use short arc welding, and the distance between the nozzle and the workpiece should be controlled at 10-15 mm;

The welding torch should move at a constant speed in a straight line, and the tungsten electrode should be aligned with the center of the weld seam, and the wire should be fed back and forth at a constant speed;

There should be windproof facilities at the welding site, and there should be no airflow.

The welded parts should be preheated appropriately; Pay attention to the quality of arc initiation and termination.

2. Lack of penetration and fusion

The phenomenon of incomplete penetration during welding is called incomplete penetration.

The part where the weld bead does not fully melt and bond with the base metal or between weld beads during welding is called incomplete fusion.

Reasons:

1) The welding current control is too low, the arc is too long, the welding speed is too fast, and the preheating temperature is low.

2) The weld seam gap is too small, the blunt edge is too large, and the groove angle is too small.

3) The oxide removal on the surface of the welded component and between the welding layers is not clean.

4) Not proficient in operating techniques, unable to grasp the good timing of wire feeding.

Preventive measures:

1) Choose the correct welding current parameters. When welding thick plates, preheat the workpiece to 80-120 ℃ before welding to ensure that the workpiece temperature meets the welding requirements.

2) Choose appropriate welding joint gaps and groove angles.

3) Strengthen the cleaning of oxides on the surface of welded components and between welding layers.

4) Strengthening welding operation technology should correctly judge the melting situation of the groove or welding layer surface, and use high current (generally, a certain size of clean and bright molten pool should be obtained at the welding site within 5 seconds after arc ignition, and wire welding can be added at this time) to quickly weld and quickly feed with less welding wire. Careful welding can avoid the occurrence of incomplete penetration and fusion.

3. Bite the edge

After welding, the concave groove at the junction of the base metal and the weld edge is called undercutting.

Reasons:

1) The welding process parameters are too large, the welding current is too high, the arc voltage is too high, and the heat input is too large.

2) If the welding speed is too fast and the welding wire leaves the molten pool before filling the arc pit, undercutting may occur.

3) Uneven swing of the welding torch, excessive angle of the welding gun during welding, and improper swing can also cause undercutting.

Preventive measures:

1) Adjust and reduce welding current or arc voltage.

2) Appropriately increase the wire feeding speed or decrease the welding speed and dwell time at the edge of the molten pool to make the weld bead fully filled.

3) Reducing the melt width appropriately, increasing the melt depth, and improving the aspect ratio of the weld seam have a significant effect on suppressing edge biting defects.

4) The welding operation should ensure that the welding gun swings evenly.

4. Tungsten clip

The non-metallic impurities remaining in the weld metal during welding are called slag inclusions. The tungsten electrode melts and falls into the molten pool due to excessive current or collision with the workpiece welding wire, resulting in tungsten inclusion.

Reasons:

1) Incomplete cleaning before welding leads to severe oxidation of the melted end of the welding wire, resulting in slag inclusion.

2) Improper selection of the shape and welding parameters at the end of the tungsten electrode resulted in burning of the end and the formation of tungsten inclusions.

3) The welding wire was in contact with the tungsten electrode and an oxidizing gas was mistakenly used.

Preventive measures:

1) Mechanical and chemical cleaning methods can be used to remove oxides and dirt from the groove and welding wire; High frequency pulse arc ignition is used, and the melting end of the welding wire is always within the protection zone.

2) The welding current should match the shape of the tungsten electrode end.

3) Improve operational skills, avoid contact between welding wire and tungsten electrode, and update inert gas.

5. Burn through

Due to the high temperature of the molten pool and delayed filling of the wire, the welding molten metal flows out of the groove and forms a perforation defect.

Reasons:

1) Excessive welding current.

2) The welding speed is too slow.

3) The groove form and assembly clearance are unreasonable.

4) The welder has a low level of operational skills.

Preventive measures:

1) Reduce the welding current appropriately.

2) Appropriately increase the welding speed.

3) The groove processing should comply with the specifications, and the assembly gap can be adjusted to increase the blunt edge and reduce the root gap.

4）Better the operation technique

6. Weld bead overburning and oxidation

Severe oxidation products are produced on the inner and outer surfaces of the weld bead.

Reasons:

1) The tungsten electrode is not concentric with the nozzle.

2) The gas protection effect is poor, the gas purity is low, and the flow rate is small.

3) The temperature of the molten pool is too high.

4) The tungsten electrode extends too far and the arc length is too long.

Preventive measures:

1) Adjust the concentricity between the tungsten electrode and the nozzle.

2) Ensure gas purity and increase gas flow rate appropriately.

3) Increase the current appropriately, improve the welding speed, and fill the wire in a timely manner.

4) Shorten the tungsten electrode extension appropriately and reduce the arc length.  

7. Crack

Under the influence of welding stress and other factors, the bonding force of metal atoms in the local area of the welded joint is destroyed, resulting in gaps.

Reasons:

1) Unreasonable welding structure, excessive concentration of welds, and excessive restraint of welded joints.

2) The size of the melt pool is too large, the temperature is too high, and there is a lot of alloy element burnout.

3) The arc is stopped too quickly, the arc pit is not fully filled, and the welding wire is withdrawn too quickly;

4) The fusion ratio of welding materials is not suitable. When the melting temperature of the welding wire is too high, it can cause liquefaction cracks in the heat affected zone.

5) Improper selection of alloy composition for welding wire; When the magnesium content in the weld is less than 3%, or the iron and silicon impurity content exceeds the specified limit, the tendency for cracks increases.

6) The arc crater is not filled and cracks appear

Preventive measures:

1) The design of welding structures should be reasonable, and the arrangement of welds can be relatively dispersed. Welds should avoid stress concentration as much as possible and the welding sequence should be selected reasonably.

2) Use a relatively small welding current or increase the welding speed appropriately.

3) The arc extinguishing operation technique should be correct. A lead out plate can be added at the arc extinguishing point to avoid extinguishing too quickly, or a current attenuation device can be used to fill the arc pit.

4) Correctly select welding materials. The composition of the selected welding wire should match the base material.

5) Add a starting arc plate or use a current attenuation device to fill the arc pit.