Overall analysis of laser welding technology for aluminum alloy
Aluminum alloy laser welding heating concentration is large, weld depth to width ratio is large, welding structure deformation is small, but there are also some disadvantages:
(1) The laser focus diameter is small, which requires high precision of workpiece welding assembly.General assembly clearance and side offset should be less than 0.1mm or 10% of the plate thickness, which increases the difficulty of implementation of complex THREE-DIMENSIONAL welding structures.
(2) Since aluminum alloy has a reflectivity of up to 90% to laser at room temperature, the laser deep fusion welding of aluminum alloy requires a high-power laser.Laser welding of aluminum alloy sheet research indicates that deep penetration laser welding of aluminium alloy double depends on the laser power density and energy threshold, the laser power density and linear energy limit the molten pool behavior of welding process, and ultimately reflected in the weld characteristics, for full penetration welding process parameter optimization can be on the back of the weld width ratio evaluation;
(3) the low melting point, good liquid metal flow, under the action of high power laser have a powerful metal evaporation, with a hole in the effect of welding in the process of metal vapor plasma cloud/performance of the absorption of laser energy, deep influence in aluminum alloy welding process is not stable, weld easy to produce the defects such as porosity, surface subsidence, bite edge;
(4) Laser welding has fast heating and cooling speed and higher weld hardness than arc.However, due to the burning loss of alloying elements during laser welding of aluminum alloy, the strengthening effect of aluminum alloy is affected, so there is still the problem of aluminum alloy welding seam softening, which reduces the strength of aluminum alloy welding joint.Therefore, controlling welding defects and improving welding joint performance are the main problems in laser welding of aluminum alloys.
Stomatal control steps of laser deep fusion welding of aluminum alloy are as follows:
Before welding technology
The surface treatment before welding is an effective method to control the porosity of laser welding of aluminum alloy.Surface treatment methods usually include physical, mechanical and chemical cleaning.In recent years, laser shock cleaning has also appeared, which will further improve the degree of automation of laser welding.
Stability control technique
The process parameters of laser welding of aluminum alloy usually include laser power, defocus, welding speed, gas protection composition and flow rate, etc.These parameters not only affect the protection effect of welding area, but also affect the stability of laser deep penetration welding process, thus affecting the porosity of welding seam.When the laser power density of thin plate laser welding matches the line reasonably, the back width ratio of weld can be effectively guaranteed and the porosity rate of weld can be controlled.
Double spot welding technique
Double-point laser welding is a welding process in which two focused laser beams act on the same pool at the same time.During laser deep penetration welding, one of the main causes of weld porosity is that the gas in weld pool hole is sealed when the weld is closed.In the case of double-point laser welding, the large opening of the hole is conducive to the steam escaping from the metal and the stability of the hole due to the effect of two light sources, thus reducing the porosity of the weld.
Laser arc composite welding technology
Laser arc composite welding is a welding method in which laser and arc weld in the same pool.In general, laser is the main heat source. The interaction between laser and arc is used to improve the depth and speed of laser welding and reduce the welding assembly precision.Filler wire is used to adjust the structure and performance of welding joint, and arc is used to improve the stability of laser welding hole, thus reducing the porosity of welding seam.In the laser arc composite welding process, the metal vapor/plasma cloud generated by the laser process is affected by the arc, which is beneficial to the absorption of laser energy and the stability of the hole.
Optical fiber laser welding technology
The keyhole effect in laser deep fusion welding is caused by the intense vaporization of metal under laser action.The vaporizing steam force of metal is closely related to laser power density and beam quality, which not only affects the penetration depth of laser welding, but also affects the stability of keyhole.
Pulse laser welding process
Compared with continuous laser welding, laser output adopts pulsating mode, which can promote the formation of periodic and stable flow in the molten pool, facilitate the bubble to escape from the molten pool, and reduce the porosity of welding seam.When the pulse amplitude increases, the porosity of weld decreases, that 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 after 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.