1. Easy Oxidation - The Oxide Film Problem
Challenge: an aluminum oxide film (Al₂O₃, melting point about 2050 °C) forms easily on the surface of aluminum alloy plates and absorbs moisture. During welding it hinders melting of the base metal and easily forms defects such as pores, slag inclusions and incomplete fusion, degrading weld performance.
Solution: remove the oxide film mechanically (stainless wire brush or chemical cleaning) immediately before welding, use AC TIG welding with the cleaning action of the electrode-positive half-cycle, and protect the molten pool with argon shielding.
2. Porosity - Hydrogen Solubility Collapse
Challenge: porosity is the most common defect in aluminum welding, caused mainly by hydrogen. Liquid aluminum dissolves large amounts of hydrogen while solid aluminum dissolves very little; when the molten pool cools and solidifies rapidly, hydrogen forms pores in the weld.
Solution: eliminate the hydrogen sources - dry the filler wire and base metal, remove moisture, oil and grease, use high-purity argon, and control welding speed so dissolved gas can escape before solidification.
3. Weld Deformation and Hot Cracking
Challenge: aluminum's thermal expansion coefficient and shrinkage are about twice those of steel, and its wide solidification range promotes hot cracking. Large internal stresses from welding deformation, combined with structural restraint, can lead to thermal cracks.
Solution: use proper joint design (backing bars, pre-strain or clamping), control heat input, weld with appropriate filler alloys (for example 4043 for 6xxx series) and sequence welds to balance shrinkage.
4. High Thermal Conductivity
Challenge: aluminum conducts heat roughly three to four times better than steel, so welding aluminum alloy plates consumes more heat and the heat spreads rapidly away from the joint.
Solution: use high-current, high-speed welding to concentrate heat, preheat thick sections, and use a power source with the required current density.
5. Evaporation Loss of Alloy Elements
Challenge: aluminum alloys containing low-boiling-point elements (such as magnesium, zinc and manganese) suffer significant evaporation losses under the high-temperature arc, changing the chemical composition of the weld metal and reducing weld performance.
Solution: control arc energy and welding speed to limit overheating, use filler metals that compensate for element loss, and avoid excessive current density.
6. Low High-Temperature Strength and Plasticity
Challenge: the strength and plasticity of aluminum at high temperature are very low; the weld metal can lose its shape, and the molten pool is easily disturbed, causing weld sagging or collapse.
Solution: use backing bars or backing gas to support the root, weld in appropriate positions, and control the molten pool size.
Summary
Aluminum alloy welding is demanding but fully manageable: clean and dry the surfaces, shield with argon, control heat input, choose the right filler metal and use proper joint design. Applied together, these measures produce sound aluminum welds in production.
