Analysis of laser welding technology and characteristics of aluminum alloy

Welding characteristics

   Aluminum alloy laser welding heating concentration, weld depth to width ratio, welding structure deformation is small, but there are some shortcomings:

(1) The small diameter of laser focusing spot leads to high requirements for workpiece welding and assembly precision. Generally, the assembly clearance and the amount of side misalignment should be less than 0.1mm or 10% of the plate thickness, which increases the implementation difficulty of the complex THREE-DIMENSIONAL welding structure.

(2) As the reflectivity of aluminum alloy to laser is as high as 90% at room temperature, the laser deep fusion welding of aluminum alloy requires a high power of laser.Laser welding of aluminum alloy sheet to study indicates that deep penetration laser welding aluminum alloy double line depends on the laser power density and energy threshold, the laser power density and linear energy restricts the molten pool behavior of welding process, and ultimately reflect on weld forming characteristics, for full penetration weld process optimization can through the back width of weld parameter ratio evaluation;

(3) the low melting point, good liquid metal flow, under the effect of high power laser produced strong metal vaporization, with holes in the process of welding effect formed by metal vapor plasma cloud/performance to influence on the absorption of laser energy, aluminum alloy lead to deep fusion welding process is not stable, weld prone to defects such as porosity, surface subsidence, bite edge;

(4) Laser welding has a fast heating and cooling speed, and the hardness of welding seam is higher than that of arc. However, due to the burning loss of alloy elements in laser welding of aluminum alloy, which affects the strengthening effect of alloy, there is still a problem of softening of aluminum alloy welding seam, thus reducing the strength of welding joint of aluminum alloy.So the main problem of laser welding of aluminum alloy is to control weld defects and improve weld joint performance.

Stomatal control of laser deep fusion welding of aluminum alloy has the following steps:
Pre-welding technique

   Surface treatment before welding is an effective method to control the porosity of laser welding of aluminum alloy. The surface treatment methods usually include physical and mechanical cleaning and chemical cleaning. In recent years, laser impact cleaning has also appeared, which will further improve the degree of automation of laser welding.

Stability control technique

   Process parameters of laser welding of aluminum alloy usually include laser power, defocus, welding speed, and the composition and flow rate of gas protection.These parameters not only affect the protection effect of welding area, but also affect the stability of laser deep fusion welding process, thus affecting the weld porosity.When the laser power density of thin plate laser welding is matched with the line energy reasonably, the back width ratio of weld can be guaranteed and the weld porosity can be controlled effectively.

Double spot welding technique

   Double spot laser welding refers to the welding process in which two focused laser beams simultaneously act on the same pool.In the process of laser deep fusion welding, one of the main reasons for the formation of weld porosity is to seal the gas in the hole in the weld pool at the moment of closure.When double light point laser welding is used, because of the effect of two light sources, the large opening of the hole is conducive to the internal metal vapor escape and the stability of the hole, so as to reduce the porosity of the weld.

Laser arc composite welding technology

   Laser arc composite welding is a welding method in which laser and arc are applied to the same pool.Generally, the laser is the main heat source, and the interaction between laser and arc is used to improve the depth and speed of laser welding and reduce the welding assembly precision.The filler wire is used to regulate the microstructure and properties of the welded joint, and the arc is used to improve the stability of the laser welding holes, so as to reduce the porosity of the weld.

   In the laser arc composite welding process, the arc affects the metal vapor/plasma cloud induced by the laser process, which is conducive to the absorption of laser energy and the stability of the hole.

 
Optical fiber laser welding technology

  keyhole effect in laser deep penetration welding process results from the strong vaporization of metal under laser action.The vaporizing steam force of the metal is closely related to the laser power density and beam quality, which not only affects the penetration depth of laser welding, but also affects the keyhole stability.

Pulse laser welding technology

   Compared with continuous laser welding, laser output adopts pulsating mode, which can promote the molten pool to produce periodic and stable flow, which is beneficial to the bubble escaping from the molten pool and reduce the porosity of welding seam.When the pulse amplitude increases, the porosity of weld decreases, and the porosity of stainless steel decreases from 2.1% to 0.5%, and that of superalloy decreases from 7.1% to 0.5%.

Post-welding composite treatment technology

   Before welding, even if the strict surface treatment, welding process stability is good, aluminum alloy laser welding will inevitably produce weld porosity, so it is necessary to use post-welding treatment to eliminate the porosity.