Welding Aluminum and Aluminum Alloy: Tips and Techniques for Success

1. Welding materials:

1. The argon gas used for welding must have a purity of ≥ 99.99% and a dew point of ≤ -55℃, and should comply with the provisions of either GB/T4842 or GB10624. If the pressure of the bottled argon is ≤ 0.5MPa, it should not be used.

The nitrogen content of the argon should be < 0.04% to avoid the formation of light yellow or grass green magnesium nitride and pores on the weld surface. Similarly, the oxygen content should be < 0.03% to avoid the formation of dense black spots, unstable arc, and large spatter on the surface of the weld pool. If the water content is ≥ 0.07%, the weld pool will boil and gas pores will be generated in the weld.

2. A cerium tungsten electrode is commonly used for manual tungsten argon arc welding.

The electrode diameter should be selected based on the size of the welding current, with a tungsten electrode one size larger than required generally being used. The end of the electrode should be hemispherical, and this can be achieved using the following fabrication method:

Use a tungsten electrode one size larger than the required specification, grind the end into a cone, vertically clamp the electrode, start an arc on the test plate with a current 20-30A greater than the current required by the tungsten electrode, maintain it for a few seconds, and the tungsten terminal head will become hemispherical.

If the tungsten electrode is contaminated with aluminum, it must be reground or replaced. In case of slight pollution, the current can be increased to make the arc burn on the test plate for a while. This will burn away the pollutants.

3. When using MIG welding for aluminum alloys, it is important to note that the aluminum welding wire is relatively soft. Therefore, to avoid biting the wire, it is not recommended to use a wire feeding wheel with gear or a wire pushing type.

Related reading: MIG vs TIG Welding

Using spring tubes for wire feeding hoses is not allowed. Instead, polytetrafluoroethylene or nylon products should be used to prevent pollution or blockage due to grinding.

MIG welding typically uses DC reverse polarity.

4. The primary function of flux is to remove oxide film and other impurities. When using flux, it can be mixed with absolute alcohol to create a paste or directly applied as flux powder to both sides of the groove.

For fillet welds, select fluxes that can easily remove slag after welding. Flux for aluminum magnesium alloys should not contain sodium.

5. When welding aluminum materials of different grades without regulations in the drawings and processes, select welding wire materials based on the base metal with better corrosion resistance and lower strength levels.

Related reading: Guide for Selection of Solid and Flux Cored Wires

When welding corrosion-resistant aluminum alloys such as aluminum-magnesium alloy or aluminum-manganese alloy, it is recommended to use welding wires that contain magnesium or manganese content similar to or slightly higher than the base metal.

Welding wires can be chosen from GB/T10585 aluminum and aluminum alloy welding wire, GB/T3190 deformed aluminum and aluminum alloy with defined chemical composition, and GB/T3197 aluminum and aluminum alloy wire for welding rods.

Related reading: Can Aluminum and Aluminum Alloy Be Welded?

You can refer to the tables below when selecting welding wires. Table 3 and Table 4 have been extracted from the welding manual.

Table 1 welding wire for aluminum welding of the same brand

Table 2 welding wire for dissimilar aluminum welding wire

Table 3 selection of welding wires for different materials and performance requirements

Note: ER aluminum welding wire is American Standard ANSI / AWSA5.10.

2. Preparation before welding:

1. The aluminum groove should be processed using mechanical methods, including shearing. If plasma or flame cutting methods are used, any discolored areas must be removed by at least 3mm of machining.

The resulting groove surface should be flat, smooth, and free from cracks, layers, inclusions, burrs, flash, or oxidation. The surface of the groove should exhibit a silver-white metallic luster. If necessary, a 100% PT (penetrant testing) should be performed on the groove, including at least 50mm on both sides.

2. Surface cleaning, including removal of surface oxide film, scale, pollution, and unqualified oxide color, should be carried out on the welding wire, groove surface, and at least 50mm on both sides.

3. Tools such as 0.15~0.2 stainless steel wire disc brush, metal grinding head (i.e. electric milling cutter), manual disc milling machine, file (an aluminum arc file is recommended), scraper, and acetone (ensure the white cloth stained with acetone is clean, and avoid using cotton cloth or cotton yarn to prevent plush when wiping) can be used.

It should be noted that these tools should be cleaned before use, and the oxide film should not be pressed into the base metal during cleaning.

It is important to avoid using excessive force when cleaning. Grinding with a grinding wheel or ordinary sandpaper is not permitted, as aluminum is a soft material and sand particles can become embedded in it. This can result in defects such as porosity and slag inclusion after welding.

4. For outsourced hot processing parts made from aluminum, such as heads, etc., 100% PT must be carried out on the surface after they enter the factory. RT may be carried out on uncertain parts if necessary.

To clean the surface of welding wire, use a stainless steel wire brush or clean oil sandpaper. For welding wires with a thick oxide skin on the surface, chemical cleaning is required after grinding before welding.

To clean the material, soak it in a 5% to 10% NaOH solution at 70℃ for about 0.5 to 3 minutes. Then, rinse it with clean water and soak it in an HNO3 solution of approximately 15% at room temperature for about 1 to 2 minutes. After that, rinse it with warm water and dry it with a hand-held blower. Please do not use an air compressor as there might be water and oil in the air. After drying, put it into an oven at 100℃. This method is also applicable to aluminum materials.

5. Keep the cleaned welding wires and weldments clean and dry, and avoid touching the welding parts with bare hands or blowing them with the mouth. Welders should wear white welding gloves and not wear dirty gloves to avoid trouble.

Before welding, it is strictly prohibited to pollute the welding parts. Otherwise, the parts should be cleaned again, and local pollution can be removed with local cleaning. Cover both sides of the groove with white paper if possible. Welding should be done immediately after mechanical cleaning.

If no welding is performed within 4 hours after cleaning, clean the parts again before welding.

6. The assembly of weldments must be accurate. If the assembly is poor, the parts should be replaced instead of forcing them together to avoid excessive stress. Before formal welding, the groove size should be checked, and welding should only be carried out after it is qualified.

7. The welding wire and process measures selected for tack welding should be the same as the welding process.

8. During the assembly of weldments, tack welding should be avoided at stress concentration points, such as the intersection of welds and corners on the workpiece. The length and spacing of tack welds can be determined based on the following dimensions (mm).

9. The tack weld must be free of cracks, pores, slag inclusions, and other defects. Otherwise, it must be removed and rewelded. The rewelding should be carried out in the nearby area instead of spot welding in the original place. When the process does not specify the butt weld gap, it can be 2~4mm.

10. For the tack weld that will melt into the permanent weld, it is necessary to ensure full penetration and remove the oxide layer on its surface (only silver-white is allowed). Also, make a smooth transition at both ends of the weld to facilitate arc connection. Otherwise, it should be repaired. When welding on cold parts, the arc should stay for a while at the beginning of welding. Wire welding should be added in time when the base metal edge starts to melt to ensure the penetration of the beginning welding point.

11. When welding longitudinal joints, place run-on and run-off plates at both ends of the weldment. The run-on and run-off plates shall be made of aluminum materials with the same brand and thickness as the weldment. While welding circumferential weld, try to avoid arc crater as much as possible.

12. If tack welds crack during welding, resulting in plate edge dislocation or gap change, welding shall be immediately stopped, and welding can resume after repair.

13. During the welding process, clean black ash and oxide from the upper weld surface first, using a wire brush.

Pay attention to flame handling during welding, including arc stop.

Arc striking can be carried out at a distance of 10-20mm from the starting end of welding, then quickly returned to the starting end.

The first layer should be welded in a straight line.

To obtain a good shape, the other layers can swing laterally and stop at both sides for fusion.

14. Aluminum is prone to deformation and collapse during welding; therefore, clamps and backing plates should be made before welding.

When using clamps, both the front and back sides of the parts need to be clamped, and the rigidity and clamping force of the clamps should be moderate. A clamping force that is too small cannot control deformation, while a force that is too large can easily lead to weld cracking due to excessive weld restraint.

The clamping force should be 350 kg/100mm.

Aluminum clamps can be made of soft carbon steel or stainless steel, but this can impede heat dissipation. On the other hand, using strengthened aluminum to make clamps can improve heat dissipation.

The longitudinal seam jig can be of piano key type, while the circumferential seam jig can be of hydraulic bulging type.

During longitudinal joint assembly, it is recommended to increase the gap appropriately to allow for contraction after welding. As for circumferential seam (including circular flange, flange, etc.), reverse staggered edges or flanges should be reserved, as the flange will deform after welding.

Backing plates are generally made of carbon steel or stainless steel. Graphite can be used to make backing plates for welding low-grade aluminum materials. It is also important to consider the cooling rate of the weld when choosing the material for the backing plate.

In cases where the aluminum plate is thick or the assembly gap of the backing plate is large, the gap can be sealed with clay mud and then removed after welding.

The size of the base plate can be as follows: