Tips for laser welding aluminum alloy

Aluminum alloy has the advantages of low density, high strength and good corrosion resistance, so it is widely used in the automotive industry, new energy, aerospace and construction industries. At present, laser welding has been widely used in the production of aluminum alloy products.battery pilot line Compared with traditional welding methods, laser welding can provide higher productivity and better welding quality, realizing high-precision welding and automation of complex structures.

Laser welding is a technology that radiates a high-intensity laser onto a metal surface, melting the metal and then cooling and crystallizing it to form a weld through thermal coupling between the laser and the metal. According to the thermal action mechanism of laser welding can be divided into two kinds of heat conduction welding and deep melting welding, heat conduction welding is mainly used in precision parts of the package welding or micro-nanometer welding;laser welding machine for lithium ion batteries laser deep melting welding is mainly used in the need for complete penetration of the material welded, the welding process will make the material vaporization, the molten pool appears in the spoon hole phenomenon, is currently the most widely used laser welding, but also the preferred way of aluminum alloy welding.

Advantage: Aluminum alloy laser welding using oscillating laser welding, no need to add auxiliary materials, welding equipment is simple, no consumables, easy to automate.

Disadvantages: high requirements for welding to the membrane, then the weld is easy to trap;ESS lithium battery machine welding starting point and end point is easy to produce a focus; welding work process to carry out stability studies in general, easy to produce defects affecting the quality of welding.

Due to the inherent physical properties of aluminum alloy, such as low laser absorption, low boiling point of alloying elements, high thermal conductivity, high coefficient of thermal expansion, wide range of solidification temperature, high solidification shrinkage, low viscosity, high liquid hydrogen absorption, etc., so it is easy to produce defects such as porosity and thermal cracks in the laser welding process.

Among them, porosity is the most likely form of defects in the laser welding process of aluminum alloy, which will destroy the denseness of the weld metal, weaken the effective cross-sectional area of the weld, and reduce the mechanical properties and corrosion resistance of the weld. Therefore, effective measures must be taken to prevent porosity and improve the internal quality of the weld.

Laser welding to inhibit porosity way

1. Inhibit weld porosity through pre-welding surface treatment

Pre-weld surface treatment is an effective method to control the metallurgical porosity of aluminum alloy laser weld.

After comparison, the chemical method (metal cleaning agent cleaning - water washing - alkaline washing - water washing - acid washing - water washing - drying) to deal with the surface of the test plate is the best process. Among them, alkali washing was done with 25NaH (sodium hydroxide) solution to remove the surface thickness of the material, and acid washing was done with 20% HN03 (nitric acid) + 2% (hydrogen fluoride) aqueous solution to neutralize the residual alkali solution. After surface treatment, the test plate is welded within 24 hours, when the test plate stays longer after treatment, it is assembled before welding and then wiped with anhydrous alcohol.

2. Inhibit weld porosity by welding process parameters

The formation of weld porosity is not only related to the quality of the surface treatment of the weldment, but also related to the welding process parameters. Welding parameters on the impact of weld porosity is mainly reflected in the melt depth of the weld, that is, the weld back width ratio on the impact of weld porosity.

The results show that when the back-to-width ratio r > 0.6, the concentration distribution of chain-like porosity in the weld can be effectively improved, and when the back-to-width ratio r > 0.8, the presence of large porosity in the weld can be effectively improved and the residual porosity in the weld can be eliminated to a large extent.

3. Inhibit welding porosity through the correct choice of shielding gas and flow rate

The choice of shielding gas directly affects the quality, efficiency and cost of welding. In the laser welding process, the correct blowing shielding gas can effectively reduce weld porosity.

Argon (argon) and helium (helium) are used to protect the weld surface. During laser welding of aluminum alloys, Ar and he have different laser ionization degrees, resulting in different weld shapes. The results show that the porosity of the weld when Ar is used as the protective gas is less than that of the weld when helium is used as the protective gas.

At the same time is also our own also need to carry out attention, the gas flow is too small welding process produces a large number of research plasma can not be blown away, so that our welding molten pool is not stable, the formation of porosity certain chances of increasing. Gas through the flow of moderate plasma to get an effective management control, protective gas on the melt pool plays a good anti-oxidation effect, the least pores. Excessive gas flow accompanied by excessive gas environment pressure, making the enterprise part of the information protection gas mixed into the solute pool inside, so that the rate of porosity increases.

Due to the influence of aluminum alloy properties, the laser welding process can not completely avoid the emergence of no porosity phenomenon, only to reduce the porosity rate. Through the process optimization before and after welding, we propose three methods to inhibit porosity for the reference of industry peers. Double Laser not only focuses on the research and innovation of laser product technology, but also explores a variety of laser processing technology, and looks forward to discussing with more industry experts in order to promote the development of laser processing technology in China.

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