Scanning multi-point composite laser welding joint

The melting point of aluminum alloy is about 660 ℃, and its reflectivity to laser is 90% higher? If the temperature reaches the critical point of 660 ℃, the laser absorption can reach 100?
The synthesis of multiple elements is highly prone to oxidation and burning, and some elements are prone to vaporization, combustion, have different melting points, and are not weldable.
The welding joints are severely softened and have a low strength coefficient, which is also the biggest obstacle to the application of aluminum alloys.
The surface is prone to the formation of refractory oxide films (Al2O3 has a melting point of 2060 ℃), which requires high-power density welding.
Aluminum alloy welding is prone to porosity and hot cracking.
The coefficient of linear expansion is large and prone to welding deformation.
Aluminum alloy has a high thermal conductivity (about 4 times that of steel), and at the same welding speed, the heat input is more than 4 times greater than that of welded steel.
Conclusion: The welding of aluminum alloys requires an efficient welding method with high energy density, low heat input, fast welding speed, and real-time controllable power for each key welding point.

The process parameters of aluminum laser welding mainly include power density, peak power, welding speed, focal position, real-time power control of each welding point, type and flow rate of shielding gas, etc., which directly determine the formation of the weld seam.
1. Power density
The power density of laser is the most important factor determining the depth of weld penetration. When other process parameters remain constant, the aspect ratio of the weld seam increases with the increase of power density. But if the power density is too high, it will cause strong vaporization of the metal, severely burn the alloy, and the grain size of the formed structure of the weld will be too large, resulting in a decrease in the strength of the weld. Single mode fiber lasers are more capable of this task with effective combination forms and processes.
2. Welding speed
When other process parameters remain unchanged, the penetration depth decreases with the increase of welding speed, and the welding efficiency increases with the increase of welding speed. However, if the speed is too fast and the energy density of the line reaching the weld seam is low, the penetration depth will not meet the welding requirements; If the speed is too slow, the linear energy density will be too high, the base material will be excessively melted and burned, the joint performance will be reduced, and even thermal cracks may occur. Therefore, for a specific thickness of aluminum alloy workpiece, there exists an optimal welding speed that can maintain a suitable weld depth to width ratio without overheating the workpiece after selecting and determining the laser power density. Aoxin learned the secrets behind it.
3. Focus position
The relationship between the focal position and penetration depth in aluminum alloy laser welding. We can see that there is a jumping process in the depth of fusion with the change of focal point position: when the focal point deviates significantly from the surface of the workpiece (≥ 2mm), the spot size on the surface of the workpiece is larger, resulting in a lower energy density of the beam, which belongs to the melting welding mainly based on thermal conduction, and the depth of fusion is shallower; When the focal point approaches a certain position on the surface of the workpiece, the energy density of the incident beam on the surface of the workpiece increases to a critical value, resulting in a pinhole effect and a jump increase in penetration depth. Through experiments, it has been found that the maximum weld penetration occurs when the focal position is 1mm above the surface of the workpiece.