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Aluminum alloy body welding technical characteristics and welding precautions
Aluminum alloys are known for their high affinity with oxygen, which allows them to easily form a dense and strong alumina layer when exposed to air. This oxide film, typically around 0.1 μm thick, has a melting point of up to 2050°C—far higher than that of aluminum itself. Its density is about 1.4 times greater than pure aluminum. During welding, this oxide layer can hinder proper metal bonding, leading to slag inclusion. Moreover, the oxide film can absorb moisture, which contributes to the formation of weld porosity. These defects can significantly reduce the mechanical properties of the welded joint. To ensure quality, it's crucial to thoroughly clean the workpiece surface before welding and protect it from re-oxidation during the process. Effective measures include mechanical grinding or chemical cleaning (such as D40) to remove oxides from the joint area, and using high-purity argon gas (99.99%) for shielding.
Aluminum and its alloys also have high thermal conductivity and specific heat capacity, meaning they quickly dissipate heat during welding. This requires the use of concentrated and powerful heat sources, especially for thick plates (8mm and above), where preheating may be necessary to achieve proper fusion.
The linear expansion coefficient of aluminum alloys is roughly twice that of steel, and their solidification shrinkage rate can reach 6.5%–6.6%, making distortion a common issue. Proper tooling, along with optimized process parameters and welding sequences, helps prevent deformation, especially in thin plates. Some alloys are prone to hot cracking due to internal stresses within the brittle temperature range, particularly in high-strength grades. Preventive measures include improving joint design, selecting appropriate welding parameters, and using compatible filler materials.
Porosity is another major challenge in aluminum welding, especially with pure aluminum and corrosion-resistant alloys. Hydrogen is the primary cause, often coming from moisture in the atmosphere, welding materials, or the parent material. The oxide layer on the wire and base metal can trap moisture, contributing to pore formation. To minimize this, all welding materials must be dried and stored properly, and welding should be done within a short time after cleaning. For TIG welding, a high current and fast speed are recommended, while MIG welding benefits from a slower speed and larger current to maintain a stable molten pool.
At elevated temperatures, aluminum alloys lose strength rapidly. At 370°C, the strength drops to only 10MPa, which can lead to poor weld formation, collapse, or burn-through. To address this, backing plates are often used during welding.
Another difficulty is that aluminum doesn’t change color when melting, making it hard for welders to judge the correct temperature. Operators must rely on experience and use flat welding positions to better control the arc.
In summary, welding aluminum and its alloys presents several unique challenges, including oxidation, thermal management, distortion, porosity, and low high-temperature strength. Successful welding requires strict preparation, proper technique, and careful material selection. Cleaning the wire and joint area with acetone, using stainless steel brushes to remove oxides, and welding within 2 hours after cleaning are essential steps. Tungsten electrodes made of tantalum-tungsten are preferred, and argon gas with purity above 99.96% and moisture content below 50 mg/m³ is required. Lastly, the ambient temperature should not drop below 5°C; if it does, preheating to 100–200°C is necessary to ensure optimal welding conditions.