Heilongjiang Junhe Building Materials Technology Co., Ltd , https://www.junhejiancai.com
Aluminum alloy body welding technical characteristics and welding precautions
Aluminum and its alloys possess unique properties that make them challenging to weld. One of the primary issues is their strong affinity with oxygen, which leads to the formation of a dense alumina layer on the surface. This oxide film, approximately 0.1 μm thick, has a melting point of up to 2050°C—far higher than that of aluminum itself. The high density of this film, about 1.4 times that of aluminum, can hinder proper bonding during welding and cause slag inclusion. Additionally, the oxide layer absorbs moisture, which can lead to porosity in the weld. These defects significantly reduce the mechanical performance of the welded joint. To ensure quality, the surface must be thoroughly cleaned before welding, and effective shielding gas (like 99.99% argon) should be used to prevent re-oxidation.
Aluminum and its alloys also have high thermal conductivity and specific heat capacity, causing rapid heat dissipation during welding. This necessitates the use of high-energy, concentrated heat sources, especially for thicker sections, where preheating may be required. The linear expansion coefficient of aluminum alloys is about twice that of steel, leading to significant distortion during welding. To minimize deformation, suitable welding tools and proper process parameters are essential, particularly when working with thin plates. Some aluminum alloys are prone to hot cracking due to internal stresses within the brittle temperature range, making it crucial to optimize joint design and filler material selection.
Porosity is another common issue in aluminum welds, mainly caused by hydrogen. Moisture from the atmosphere, welding materials, or the oxide layer on the parent metal can introduce hydrogen into the weld pool. As the molten metal solidifies, dissolved gases may not escape, resulting in voids. Controlling hydrogen sources is vital, including drying all materials and limiting exposure time after cleaning. For TIG welding, a high current and speed are recommended, while MIG welding benefits from slower speeds to allow gas escape.
At elevated temperatures, aluminum’s strength decreases significantly. At 370°C, its strength drops to around 10MPa, making it difficult to maintain weld integrity. In such cases, backing plates are often used to support the molten metal and prevent burn-through. Another challenge is that aluminum does not change color when melting, making it hard for operators to judge the correct temperature. Skilled welders must rely on techniques like flat welding and using a lead plate to initiate the arc.
In summary, welding aluminum and its alloys requires careful preparation, precise control of environmental conditions, and appropriate welding techniques. Proper cleaning of the workpiece and wire, the use of high-purity shielding gas, and attention to temperature and humidity are all critical factors in achieving successful welds.