Practical Techniques: Three Ways to Suppress Porosity in Laser Welding of Aluminum Alloys
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Release date:
2021-04-29
Aluminum alloys boast advantages such as low density, high strength, and excellent corrosion resistance, making them widely used in industries like automotive, new energy, aerospace, and construction. Currently, laser welding has become a dominant technique in the production of aluminum alloy products. Compared to conventional welding methods, laser welding delivers higher productivity, superior weld quality, enables precise welding of complex structures, and facilitates seamless integration with automation systems.
Laser welding is a technique that involves directing high-intensity laser radiation onto a metal surface, where the interaction of laser energy with the metal—through thermally induced coupling—causes the metal to melt and subsequently solidify as it cools, forming a weld seam. Depending on the thermal mechanism at play, laser welding can be categorized into two types: conduction welding and deep-melt welding. Conduction welding is primarily used for precision component packaging or micro- and nano-scale welding applications, while deep-melt laser welding is ideal for materials requiring full penetration. During this process, the material vaporizes, creating a keyhole phenomenon within the molten pool. This method is currently the most widely adopted form of laser welding and remains the preferred approach for welding aluminum alloys.
Characteristics of Laser Fusion Welding
01
Advantages:
Laser welding of aluminum alloys employs oscillating laser welding, requiring no additional materials—making the welding equipment simple, eliminating consumables, and facilitating automation.
02
Disadvantages:
The requirements for weld gaps are stringent—otherwise, the weld seam is prone to collapse. Additionally, the weld start and end points tend to develop unevenness. Overall, the welding process lacks stability and is susceptible to welding defects.
03
Case:
Construction and Interior Design Industry—Welding of 5-Series Aluminum Alloy Door Frames
Due to the inherent physical properties of aluminum alloys—such as their low laser absorption, low boiling points of alloying elements, high thermal conductivity, high thermal expansion coefficient, a relatively wide solidification temperature range, significant solidification shrinkage, low viscosity, and high hydrogen absorption in the liquid state—they are prone to defects like porosity and hot cracks during laser welding.
Among these, porosity is the most common defect encountered during laser welding of aluminum alloys. It compromises the density of the weld metal, reduces the effective cross-sectional area of the weld, and diminishes both the mechanical strength and corrosion resistance of the joint. Therefore, it is essential to implement effective measures to prevent porosity and enhance the overall quality of the weld's internal structure.
Laser Fusion Welding Method for Pore Suppression
01
Suppressing welding porosity through pre-weld surface treatment methods
Pre-weld surface treatment is an effective method for controlling metallurgical porosity in aluminum alloy laser welds. Common surface treatment techniques include physical-mechanical cleaning and chemical cleaning.
After comparison, the process of chemically treating the test plate surface—starting with metal cleaner cleaning, followed by water rinsing, alkaline washing, another water rinse, acid pickling, a final water rinse, and finally drying—proved to be the most effective. During alkaline washing, a 25% NaOH (sodium hydroxide) aqueous solution is used to remove surface material buildup. For acid pickling, a mixture of 20% HNO₃ (nitric acid) and 2% HF (hydrofluoric acid) in water is applied to neutralize any remaining alkaline residue. The treated test plates should be welded within 24 hours; if they are left standing for an extended period before welding, they must be wiped clean with anhydrous alcohol prior to assembly.
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Suppressing Welding Porosity Through Welding Process Parameters
The formation of weld porosity is influenced not only by the quality of the workpiece surface preparation but also by the welding process parameters. Specifically, welding parameters affect weld porosity primarily through their impact on weld penetration—particularly the relationship between the weld back width ratio and porosity.
Testing has shown that when the weld back width ratio R exceeds 0.6, it effectively mitigates the concentrated distribution of string-like porosity within the weld. Furthermore, when the back width ratio R is greater than 0.8, it not only significantly improves the presence of large pores in the weld but also virtually eliminates residual porosity throughout the weld.
03
By correctly selecting the shielding gas and adjusting its flow rate, welding porosity can be minimized.
The selection of shielding gas directly affects the quality, efficiency, and cost of welding. During laser welding, properly introducing the shielding gas can effectively minimize porosity in the weld seam.
As shown in the figure above, Ar (argon) and He (helium) were used to protect the weld surface during aluminum alloy laser welding. During the process, Ar and He exhibit different degrees of ionization under the laser beam, leading to variations in weld bead formation. As a result, the porosity rate of the welds produced using Ar as the shielding gas was generally lower compared to those obtained with He as the protective gas.
At the same time, we should also note that when the gas flow rate is too low (<10 L/min), the large amount of plasma generated during welding cannot be effectively blown away, leading to an unstable weld pool and increasing the likelihood of porosity formation. On the other hand, a moderate gas flow rate (around 15 L/min) ensures effective plasma control, allowing the shielding gas to provide excellent anti-oxidation protection for the molten pool—and minimizing porosity. However, excessively high gas flow rates, accompanied by elevated gas pressure, can cause some of the shielding gas to mix into the molten pool itself, thereby raising the porosity level.
Laser welding of aluminum alloys has long been a challenging issue in the industry due to inherent material properties, making it impossible to completely eliminate porosity defects during the welding process—though the porosity rate can certainly be reduced. Through meticulous process optimization before and after welding, combined with experimental findings, we’ve identified and summarized three effective methods for minimizing porosity, offering valuable insights for our industry peers. At Chuangxin Laser, we remain committed not only to advancing research and innovation in laser technology but also to pioneering cutting-edge laser-based manufacturing processes. We look forward to collaborating with more industry experts to drive continuous improvements in China’s laser processing technologies.
Source: Chuangxin Laser
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