Aluminium and aluminium alloy products are common in our daily life because of their corrosion resistance. Laser welding of aluminium is a common method, but there are also many problems in laser welding of aluminium alloys.
This article mainly focuses on laser welding aluminium problems and solutions. I hope it will be helpful to you. Then continue reading the following article.
Common laser welding aluminium problems
Porosity Issues:
Hydrogen Porosity: Aluminum has a strong affinity for hydrogen. Moisture or hydrogen-containing contaminants on the surface or in the shielding gas can cause hydrogen pores to form during welding.
Keyhole (Keyhole) Instability: The keyhole formed during laser welding can be unstable, resulting in gas entrapment and pore formation.
Crack Issues:
Solidification Cracks: Due to the relatively large thermal expansion coefficient of aluminum and the rapid solidification during laser welding, solidification cracks can occur, especially in alloys of certain compositions.
Hot Cracks: High thermal gradients and thermal stresses during welding can cause hot cracks in aluminum.
Reflectivity Issues:
Aluminum has a high reflectivity to laser light, especially in the visible and near-infrared range. This reduces the absorption efficiency of the laser energy and requires higher laser power or special surface treatment to ensure proper welding.
Oxide Layer Issues:
A stable oxide layer forms on the aluminum surface. This oxide layer affects the weld quality and may require additional cleaning or special welding techniques to overcome its negative effects.
How to avoid porosity problems when laser welding aluminum?
Materials
Cleaning materials:
Before welding, thoroughly clean the surface of the aluminum material from impurities such as oil, dust and oxides. Chemical cleaning, mechanical grinding or ultrasonic cleaning can be used. For example, use organic solvents such as acetone to wipe off oil stains, and use sandpaper to polish to remove the surface oxide layer.
Ensure that the raw material storage environment is dry to prevent the aluminum material from absorbing moisture.
Material drying:
Dry the aluminum material, especially in an environment with high humidity. The drying temperature and time can be determined according to the specifications and moisture content of the material. Generally, it can be dried at a temperature of 100-200℃ for several hours.
Welding process
Optimize shielding gas:
Choose a suitable shielding gas, such as argon. The purity of argon should be as high as possible, generally required to be above 99.99%.
Control the flow and pressure of the shielding gas. The flow rate is usually in the range of 10-30L/min, and the pressure is adjusted according to the welding environment and weld requirements to ensure that the gas can effectively cover the welding area and prevent air from entering.
Double-layer airflow protection can be used, that is, in addition to the normal protective airflow, an auxiliary airflow is added around the laser beam to further improve the protection effect.
Control welding parameters:
Adjust parameters such as laser power, welding speed and focus position. Properly increasing the laser power can make the molten pool more stable, but too high may lead to excessive penetration and increased pores. Too fast welding speed will make the molten pool unstable and prone to pores. Usually the welding speed is between 1-5m/min. The focus position should be precisely adjusted according to the material thickness and welding requirements.
When using pulsed laser welding, optimize the pulse frequency and pulse width. For example, for thinner aluminum plates, a higher pulse frequency and a narrower pulse width can be selected to reduce heat input and the formation of pores.
Welding environment
Control environmental humidity:
Try to perform welding operations in a dry environment, and the environmental humidity can be controlled below 50% by using dehumidification equipment.
How to choose shielding gas for laser welding of aluminum?
Gas Types
Argon:
Argon is the most commonly used shielding gas for laser welding of aluminum. It has stable chemical properties and is not easy to react chemically with aluminum at high temperatures.
It can effectively protect the welding area, prevent aluminum from reacting with oxygen, nitrogen, etc. in the air, and reduce the generation of defects such as pores and slag inclusions.
Helium:
The thermal conductivity of helium is higher than that of argon, and it can take away the heat from the welding area faster, making the weld cool faster.
It is suitable for high-speed welding and occasions with low requirements for weld heat input, but the cost of helium is relatively high.
Argon-helium mixed gas:
Mixing a certain proportion of argon and helium can combine the advantages of both. For example, adding a certain amount of helium to argon (such as 75% argon + 25% helium) can not only ensure good protection effect, but also improve welding speed and weld quality to a certain extent.
Gas Purity
- The purity of the shielding gas is generally required to be above 99.99%. High-purity gas can reduce the impact of impurity gases (such as oxygen, nitrogen, moisture, etc.) on welding quality.
- Excessive impurity gas content will lead to increased defects such as weld oxidation and pores.
Gas flow rate
- The gas flow rate is determined according to the welding process parameters (such as laser power, welding speed, weld shape, etc.) and the size of the weld.
- Normally, the gas flow rate is in the range of 10-30L/min. For thicker aluminum plates or high-speed welding, the gas flow rate may need to be appropriately increased.
- Too small a flow rate may lead to insufficient protection, while too large a flow rate may cause gas turbulence and affect the protection effect.
Conclusion
During the laser welding process, due to the special characteristics of aluminum, some other problems will arise. Before welding aluminum and aluminum alloys, it is necessary to consider whether the welding quality is stable and the appearance of the weld. With the continuous improvement of laser technology and aluminum manufacturing technology, the process of laser welding aluminum has been greatly improved, laying a solid foundation for the manufacture of lightweight metal structural parts.
Aluminium welding issues
How to detect the purity of the gas when laser welding aluminum
Use a gas analyzer to detect the impurity components in the gas through professional gas analysis equipment to determine whether its purity meets the requirements.
What is the ratio of argon and helium mixed gas when welding aluminum?
70% helium + 30% argon or 75% helium + 25% argon is commonly used for high-speed welding; 50% helium + 50% argon or 30% helium + 70% argon is used for general welding.
What is the effect of the flow rate of the shielding gas on the welding quality during welding?
- Too small flow rate: leads to insufficient protection of the welding area, oxidation of the weld metal, generation of pores, and affecting the quality of the weld.
- Too large flow rate: causes gas turbulence, may involve air to destroy the protection effect, and will also interfere with the molten pool to make the weld formation worse.
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