Aluminum alloy has very low density and is light; however, it has high strength, comparable to or even superior to that of high-quality steel. It is malleable, easy to process into different profiles and has excellent electrical and thermal conductivity and corrosion resistance.
Aluminum alloy is widely used in industries such as automotive, aerospace, mechanical manufacturing and shipbuilding, making it one of the most widely used alloy materials. Hard aluminum alloys belong to the Al-Cu-Mg system and generally contain a small amount of Mn.
They can be heat treated for reinforcement, characterized by high hardness but low plasticity. Superhard aluminum belongs to the Al-Cu-Mg-Zn system, can also be heat treated for strengthening, and has the highest strength among aluminum alloys at room temperature.
However, it has low corrosion resistance and softens quickly at high temperatures. Wrought aluminum alloys are mainly Al-Zn-Mg-Si alloys. Although they contain many types of elements, the quantities are small, so they have excellent thermoplasticity and are suitable for forging.
With the rapid development of industrial levels, the demand for aluminum alloy welded structures is increasing, thus promoting in-depth research on the welding performance of aluminum alloys.
I. An introduction and advantages of MIG welding of aluminum alloys”
The main welding processes for aluminum alloys include tungsten inert gas (TIG) welding, metal inert gas (MIG) welding, friction stir welding, and resistance welding.
MIG welding is an arc welding process that uses protection using argon gas or a mixture of inert and active gases. The fundamental difference between MIG and TIG welding is the replacement of the torch's tungsten electrode with a metal wire.
In MIG welding, the wire is melted by the arc and fed into the welding zone, driven by power-driven rollers that feed the wire from the coil to the torch according to welding needs. The shielding gases used in both processes are different; 1% oxygen is added to argon gas to improve arc stability.
There are also differences in spray transfer, pulsed spray, globular transfer and short circuit transfer.
DC power, not AC, is the heat source for MIG welding. This is due to the effects on arc stability and consistency during the welding process if DC power is not used. For situations where AC welding is not used, positive DC polarity and reverse DC polarity are two different selection options, with MIG welding typically using reverse DC polarity.
This is because the arc is stable when DC reverse polarity is chosen and produces a better effect that effectively prevents the formation of a metal oxide film during welding, which is very beneficial for magnesium, aluminum and their alloys.
Lastly, when using DC reverse polarity, the wire melting speed is faster and the production efficiency is higher. MIG welding is reliable and produces consistently high-quality results, making it best suited for welding medium-thickness plates of aluminum and aluminum alloys.
II. Key Points to Consider in MIG Welding
Problems such as misalignment and deformation may occur during the MIG welding process. Therefore, the following issues must be addressed carefully during operations.
1. Misalignment between welding components
In MIG welding, misalignment between components can easily occur due to faulty tool accessory design or non-standard operations. This necessitates the need for careful fixing and meticulous attention during assembly.
2. Sheet deformation problems
Even with ideal tools, aluminum alloy sheets can still deform due to the excessive heat produced in the MIG welding process, leading to warping of the entire sheet. Small deformations can be corrected by hammering evenly with a wooden mallet.
However, severe deformation requires flame heating, adjusting the flame temperature and time to achieve the desired shape.
3 . Black oxide in MIG welding of aluminum alloy
The black residue produced during MIG welding of aluminum mainly consists of oxides such as magnesium oxide and manganese oxide. The presence of excessive black oxide during single-layer welding typically indicates insufficient shielding.
During multilayer welding, the appearance of black oxide in the root pass indicates good penetration, as the molten metal oxidizes in the air below the weld and rises to the surface.
If black oxide appears in the coating passage, this suggests inadequate shielding. With sufficient shielding, two bright white bands should appear on each side of the weld.
III. Dangers of Aluminum Alloy MIG Welding Powder
Aluminum alloy has a low melting point and generates substantial amounts of aluminum oxide dust under high-temperature arcing, posing a significant risk to workers' respiratory systems.
Additionally, the alloying elements of aluminum alloy can create harmful oxide particles during operation. Despite their low concentration, these alloy element oxides can still harm human health.
Aluminum alloy MIG welding powder can cause diseases such as pneumoconiosis, dementia, osteomalacia and anemia, necessitating effective protection against it.
4. Dust protection measures of aluminum alloy MIG welding
The fundamental purpose of aluminum alloy MIG welding dust protection is to prevent the inhalation of harmful dust. Experience shows that if aluminum alloy welding operations are infrequent in the production environment, a filtering respirator can often be sufficient to prevent workers from inhaling harmful dust.
However, if aluminum alloy welding operations are frequent, relying on filtration alone is insufficient. Comprehensive use of filtering respirators and effective ventilation systems is required.
Furthermore, for MIG welding of aluminum alloy, the use of a pulsed power source can not only improve the welding quality but also decrease the generation of aluminum oxide dust. In work environments where MIG welding of aluminum alloy is performed, workers' skin and clothing are subject to dust accumulation.
Once welding dust settles in these areas, it can harm workers' health, and regular cleaning of hands and clothing is necessary to ensure safety.
Overall, although dust from MIG welding of aluminum alloys poses a significant risk to human health, this risk can be effectively controlled by strengthening production management and raising worker awareness of protection in the manufacturing process itself.
