SHINHOP laser

Many users do not understand the impact of materials on laser welding of aluminum alloys. We all know that different materials have different absorption rates for lasers. Even for the same material, if the environment is different, the surface cleanliness is different, and the surface process is different, it will also affect the welding quality. Therefore, although laser welding is good, its basic requirements also need to be taken seriously. For laser welding of aluminum alloy materials, we need to first understand the characteristics of aluminum alloys.
High-strength aluminum alloys have high specific strength and specific stiffness, good corrosion resistance, processing performance, and mechanical properties. They have become indispensable metal materials for lightweight manufacturing in transportation fields such as aerospace and ships, with the most applications in aircraft. Welding technology has unique advantages in improving the utilization of structural materials, reducing structural weight, and achieving low-cost manufacturing of complex and dissimilar material structures, among which aluminum alloy laser welding technology is a hot topic of concern.
Compared with conventional melting welding, aluminum alloy laser welding has concentrated heating, a large weld depth-to-width ratio, and small deformation of the welded structure. However, there are also some shortcomings, which can be summarized as follows:
1. The small diameter of the laser focus spot leads to high precision requirements for the assembly of workpieces. Typically, the assembly gap and misalignment must be less than 0.1mm or 10% of the plate thickness, which increases the difficulty of implementing complex three-dimensional welded structures.
2. Due to the high reflectivity of aluminum alloys to lasers, which can reach 90% at room temperature, aluminum alloy laser deep melting welding requires the laser to have a high power. Research on laser welding of aluminum alloy thin plates shows that aluminum alloy laser deep melting welding depends on the dual thresholds of laser power density and line energy. The laser power density and line energy jointly restrict the behavior of the molten pool during the welding process, which ultimately reflects on the forming characteristics of the weld. The process optimization for fully penetrated welds can be evaluated through the back width ratio of the weld forming characteristics.
3. Aluminum alloys have a low melting point and good fluidity of liquid metal. Under the action of high-power lasers, strong metal vaporization occurs, and the metal vapor/light-induced plasma cloud formed during the welding process, accompanied by the keyhole effect, affects the absorption of laser energy by aluminum alloys, leading to an unstable deep melting welding process. The weld is prone to defects such as porosity, surface collapse, and burn-through.
4. The rapid heating and cooling speed of laser welding results in a higher weld hardness compared to arc welding. However, due to the burning loss of alloying elements in aluminum alloy laser welding, which affects the strengthening effect of the alloy, aluminum alloy welds still have a softening problem, thus reducing the strength of aluminum alloy welded joints. Therefore, the main issues in aluminum alloy laser welding are controlling weld defects and improving the performance of welded joints.

So, how can we better avoid related defects when engaging in aluminum alloy laser welding?
1. Pre-welding treatment methods
Pre-welding surface treatment is an effective method to control metallurgical porosity in aluminum alloy laser welds. Common surface treatment methods include physical mechanical cleaning, chemical cleaning, and in recent years, laser shock cleaning, which will further improve the automation level of laser welding.
2. Optimization and control of parameter stability
The process parameters of aluminum alloy laser welding typically include laser power, defocus amount, welding speed, and the composition and flow rate of gas protection. These parameters affect both the protective effect of the welding area and the stability of the laser deep melting welding process, thus influencing weld porosity. Research on aluminum alloy thin plate laser deep melting welding has found that the stability of keyhole penetration affects the stability of the molten pool, which in turn affects the weld formation and causes weld porosity defects. Moreover, the stability of laser deep melting welding is related to the matching of laser power density and line energy. Therefore, determining reasonable process parameters for stable weld formation is an effective measure to control porosity in aluminum alloy laser welds.
Research results on the forming characteristics of fully penetrated stable welds show that the ratio of the back width of the weld to the surface width of the weld (back width ratio) can be used to evaluate the forming and stability of aluminum alloy thin plate welds. When the laser power density and line energy are reasonably matched during thin plate laser welding, a certain weld back width ratio can be guaranteed, effectively controlling weld porosity.
3. Dual spot laser welding
Dual spot laser welding refers to the welding process where two focused laser beams act simultaneously on the same molten pool. During the process of laser deep melting welding, the instantaneous closure of the gas in the keyhole is one of the main reasons for the formation of weld porosity. When using dual spot laser welding, the action of the two light sources causes a larger opening of the keyhole, which is beneficial for the internal metal vapor to escape and also helps stabilize the keyhole, thereby reducing weld porosity. Studies on laser welding of A356, AA5083, 2024, and 5A90 aluminum alloys have shown that dual spot laser welding can significantly reduce weld porosity.
4. Laser-arc hybrid welding
Laser-arc hybrid welding is a welding method that combines laser and arc action on the same molten pool. Generally, laser is the main heat source, and the interaction between laser and arc is utilized to increase the melting depth and welding speed while reducing the precision requirements for welding assembly. By using filler wire to control the microstructure of the welded joint and utilizing the auxiliary effect of the arc to improve the stability of the laser welding keyhole, it is beneficial to reduce weld porosity.
During the laser-arc hybrid welding process, the arc influences the metal vapor/plasma cloud induced by the laser process, which is beneficial for the material's absorption of laser energy and the stability of the keyhole. Research results on aluminum alloy laser-arc hybrid welding seams have also confirmed its effectiveness.
5. Fiber laser welding
The small hole effect in the laser deep melting welding process originates from the intense vaporization of metal under the action of laser. The vapor force of the metal vapor is closely related to the laser power density and beam quality, which not only affects the melting depth of laser welding but also the stability of the small hole. Research by Seiji et al. on high-power fiber lasers for SUS304 stainless steel shows that during high-speed welding, the molten pool is elongated, suppressing spatter, stabilizing small hole fluctuations, and preventing bubble formation at the small hole tip. When fiber lasers are used for high-speed welding of titanium alloys and aluminum alloys, pore-free welds can also be obtained. Research by Allen et al. on the control technology of protective gas in titanium alloy fiber laser welding shows that by controlling the position of the protective gas, gas entrapment can be prevented, reducing the small hole closure time, stabilizing the welding small hole, and changing the solidification behavior of the molten pool, thereby reducing weld porosity.
6. Pulsed Laser Welding
Compared to continuous laser welding, the laser output uses a pulsed mode, which encourages periodic stable flow in the molten pool, aiding in the escape of gas bubbles and reducing weld porosity. TY Kuo and SL Jeng investigated the impact of the laser power output mode in YAG laser welding on the porosity and performance of welds in SUS 304L stainless steel and Inconel 690 high-temperature alloy. The findings indicate that for square wave pulsed laser welding, when the base power is set at 1700W, an increase in pulse amplitude ΔP leads to a reduction in weld porosity, with the porosity rate of stainless steel decreasing from 2.1% to 0.5%, and the porosity rate of the high-temperature alloy decreasing from 7.1% to 0.5%.
7. Post-Weld Composite Treatment Technology
In practical engineering applications, even with strict surface treatment before welding and good stability during the welding process, aluminum alloy laser welding will inevitably produce weld porosity. Therefore, it is important to use post-weld treatment methods to eliminate pores. This method currently mainly involves post-weld modification. Hot isostatic pressing technology is one of the methods to eliminate internal pores and shrinkage in aluminum alloy castings. Combining this with post-weld stress heat treatment for aluminum alloys forms a composite process of hot isostatic pressing and heat treatment for aluminum alloy laser welded components, which eliminates weld porosity and improves joint performance. Finally:
Laser welding technology is a profound discipline, especially when it comes to studying the characteristics of different materials, which is particularly challenging. Just the aluminum alloy material alone has already left us in awe. There is still a need for continuous in-depth research on welding process technology, with a focus on the key issues of weld porosity defects and improving welding quality.
The engineering control of aluminum alloy laser weld porosity should comprehensively consider all aspects before welding, during the welding process, and post-welding treatment, thereby improving the stability of the welding process. This leads to many new technologies and processes that need to be solved, including pre-welding treatment stages, welding parameter debugging and setting issues, control optimization, and even some laser composite welding that requires further technical research and development. Moreover, facing different materials and processes, various technical issues need to be developed and addressed one by one. Therefore, aluminum alloy laser welding is just the tip of the iceberg in our laser welding technology. To excel in laser technology, more specialized and dedicated laser welding machines are needed.