Welding method of aluminum alloy and stainless steel capable of obtaining high-strength welding joint
阅读说明：本技术 一种可获得高强度焊接接头的铝合金与不锈钢的焊接方法 (Welding method of aluminum alloy and stainless steel capable of obtaining high-strength welding joint ) 是由 尹志春 张向钧 朱文战 张可可 陈刚辉 于 2021-07-06 设计创作，主要内容包括：一种可获得高强度焊接接头的铝合金与不锈钢的焊接方法,本焊接方法采用变功率脉冲激光束和变极性脉冲电弧作为复合焊接热源对铝合金板、不锈钢板组成的搭接接头进行焊接,变功率脉冲激光束和变极性脉冲电弧采用同步脉冲调制,脉冲频率、激光功率变化频率、电弧极性转变频率、摆动频率及焊接速度之间相互配合；焊接过程中,高功率激光脉冲与正极性脉冲电弧同步,低功率激光脉冲与反极性脉冲电弧同步,变功率脉冲激光束沿垂直于焊缝方向摆动,并诱导电弧摆动。本发明通过激光束摆动精准控制焊接热源在铝合金和不锈钢的分布,并结合各种频率及焊接速度的配合,可获得界面层均匀,焊接缺陷少、综合性能优异的高强度焊接接头。(A can obtain the welding method of aluminum alloy and stainless steel of the high-strength welded joint, this welding method uses variable power pulse laser beam and variable polarity pulse electric arc as the composite welding heat source to the lap joint that aluminum alloy plate, stainless steel plate make up, variable power pulse laser beam and variable polarity pulse electric arc use the synchronous pulse modulation, the pulse frequency, laser power change frequency, electric arc polarity change frequency, swing frequency and welding speed are mutually cooperated; in the welding process, high-power laser pulses are synchronous with positive-polarity pulse arcs, low-power laser pulses are synchronous with reverse-polarity pulse arcs, and variable-power pulse laser beams swing along the direction vertical to a welding seam and induce the arcs to swing. According to the invention, the distribution of a welding heat source in aluminum alloy and stainless steel is accurately controlled through laser beam swinging, and high-strength welding joints with uniform interface layers, few welding defects and excellent comprehensive performance can be obtained by combining the matching of various frequencies and welding speeds.)
1. A welding method of aluminum alloy and stainless steel capable of obtaining a high-strength welding joint comprises the steps of respectively polishing and cleaning areas to be welded of an aluminum alloy plate and a stainless steel plate to be welded; the assembly is in a lap joint mode that the aluminum alloy plate is arranged above the stainless steel plate and below the stainless steel plate to form a workpiece to be welded, a laser beam-electric arc composite welding heat source is adopted to weld the workpiece to be welded, the composite welding heat source melts the aluminum alloy, the stainless steel is heated but not melted, and the melted aluminum alloy is spread on the unmelted stainless steel to form a brazing interface, and the aluminum alloy welding device is characterized in that:
the laser beam-electric arc composite welding heat source comprises a variable power pulse laser beam and a variable polarity pulse electric arc, the variable power pulse laser beam and the variable polarity pulse electric arc jointly act on a workpiece to be welded to form a welding pool, and the variable power pulse laser beam comprises a high-power laser pulse and a low-power laser pulse with the average power ratio of 1.5-2; the variable polarity pulse arc comprises a positive polarity pulse arc and a reverse polarity pulse arc with the average power ratio of 2-4;
the variable power pulse laser beam and the variable polarity pulse arc are modulated by synchronous pulses, the pulse frequency is recorded as f, and the f is 80Hz-120 Hz; the power change of the variable power pulse laser beam and the polarity transition of the variable polarity pulse arc are synchronous, namely the power change frequency of the variable power pulse laser beam is the same as the polarity transition frequency of the variable polarity pulse arc, and is recorded as f ', f' is 1/6f-1/3 f; the positive polarity pulse arc is synchronous with the high-power laser pulse, and the reverse polarity pulse arc is synchronous with the low-power laser pulse;
before welding, adjusting the position of a variable polarity pulse arc welding gun to ensure that when the variable polarity pulse arc welding gun arcs, the arc heat of 2/3-3/4 acts on an aluminum alloy plate, the arc heat of 1/3-1/4 acts on a stainless steel plate, and a variable power pulse laser beam is positioned on the front side of the variable polarity pulse arc welding gun along the welding direction;
in the welding process, the variable power pulse laser beam and the variable polarity pulse arc welding gun synchronously move forwards along the welding direction, wherein the moving speed is v, and v is (1/4f '-1/3 f') mm/s; while the variable power pulse laser beam advances forwards along the welding direction, the laser spot on the surface of the workpiece to be welded swings along the direction vertical to the welding seam, the swinging frequency is f ', f' -1/4 f '-1/2 f', and the average heat distribution of the swinging laser beam on the workpiece to be welded during the welding process is as follows by adjusting the position of the swinging central shaft and the swinging amplitude: 2/3-3/4 laser heat is irradiated on the aluminum alloy plate, and 1/3-1/4 laser heat is irradiated on the stainless steel plate; in the swinging process, the polarized pulse arc welding gun only moves forwards along the welding direction, and does not move in other directions, and the electric arc swings in a small range under the induction of the swinging laser beam.
2. The method of welding aluminum alloy to stainless steel for obtaining a high strength welded joint according to claim 1, wherein: after polishing and cleaning the areas to be welded of the aluminum alloy plate and the stainless steel plate to be welded and before forming a lap joint type workpiece to be welded, carrying out surface activation treatment on the areas to be welded of the stainless steel plate by using a pickling solution, and sequentially plating a Cu metal plating layer with the thickness of 5-8 microns and an Ag metal plating layer with the thickness of 5-9 microns on the surfaces of the areas to be welded of the stainless steel plate in an electric brush plating mode to form a Cu-Ag composite plating layer on the surfaces of the areas to be welded of the stainless steel plate.
3. The method of welding aluminum alloy to stainless steel for obtaining a high strength welded joint according to claim 1, wherein: the diameter of a laser spot of the variable power pulse laser beam on the surface of the workpiece to be welded is 1mm-3mm, the swing amplitude of swing in the welding process is 1mm-3mm, and the distance between the intersection point of the central axis of the variable power pulse laser beam and the surface of the workpiece to be welded and the intersection point of the central axis of the variable polarity pulse arc electrode and the surface of the workpiece to be welded is 2mm-3 mm.
4. The method of welding aluminum alloy to stainless steel for obtaining a high strength welded joint according to claim 1, wherein: the average power ratio of the high-power laser pulse to the positive polarity pulse arc is 0.6-1.5, and the average power ratio of the low-power laser pulse to the reverse polarity pulse arc is 1.3-2.
5. The method of welding aluminum alloy to stainless steel for obtaining a high strength welded joint according to claim 1, wherein: in a polarity conversion period, the ratio of the action time of the positive polarity pulse arc to the action time of the reverse polarity pulse arc is 1.5-3.
6. A method of welding of aluminium alloy to stainless steel for obtaining high strength welded joints according to any one of claims 1 to 5, wherein: the average power of high-power laser pulses in the variable-power pulse laser beam is 1500w-2200w, the average power of low-power laser pulses is 800w-1400w, the average power of positive polarity pulse arcs in the variable polarity pulse arcs is 1500w-2200w, and the average power of reverse polarity pulse arcs is 400w-800 w.
7. A method of welding of aluminium alloy to stainless steel for obtaining high strength welded joints according to any one of claims 1 to 5, wherein: the laser beam-electric arc composite welding heat source also comprises a scanning laser beam, the scanning laser beam is positioned at the rear side of the variable polarity pulse electric arc welding gun along the welding direction, and the distance between the intersection point of the central axis of the scanning laser beam and the surface of the workpiece to be welded and the intersection point of the central axis of the variable polarity pulse electric arc electrode and the surface of the workpiece to be welded is 10-15 mm; in the welding process, the scanning laser beam and the variable polarity pulse arc welding gun synchronously move forwards along the welding direction; the scanning laser beam rotationally scans the surface of the weld joint while advancing in the welding direction, and the scanning range covers the weld joint area.
8. The method of welding aluminum alloy to stainless steel for obtaining a high strength weld joint according to claim 7, wherein: the ratio of the power of the scanning laser beam to the power of the high-power laser pulse in the variable-power pulse laser beam is 0.3-0.6, and the scanning frequency of the scanning laser beam is 80Hz-300 Hz.
9. The method of welding aluminum alloy to stainless steel for obtaining a high strength welded joint according to claim 1, wherein: the scanning laser beam rotationally scans on the surface of the welding seam, and the specific mode that the scanning range covers the welding seam area is as follows: the laser focus of the scanning laser beam is controlled to rotate in the direction parallel to the surface of the welding workpiece, and meanwhile, the scanning laser beam reciprocates in the direction vertical to the surface of the welding workpiece, the frequency of the rotating motion is the same as that of the reciprocating motion, so that the scanning path of the laser focus of the scanning laser beam is parallel to the surface of the welding seam, and the scanning range of a laser spot irradiated on the surface of the welding seam just covers the surface of a welding seam area by adjusting the rotating radius.
10. The method of welding aluminum alloy to stainless steel for obtaining a high strength weld joint according to claim 7, wherein: the average power of high-power laser pulses in the variable-power pulse laser beam is 1300w-2000w, the average power of low-power laser pulses is 600w-1200w, the average power of positive polarity pulse arcs in the variable polarity pulse arcs is 1300w-2000w, the average power of reverse polarity pulse arcs is 200w-600w, and the power of scanning laser beams is 400w-1000 w.
Technical Field
The invention provides a welding method of aluminum alloy and stainless steel capable of obtaining a high-strength welding joint, and belongs to the field of welding processing.
Background
In the face of increasingly serious energy shortage problems, the light weight of vehicles is receiving more and more attention from various countries. The full stainless steel subway train body structure further uses an aluminum alloy material to replace part of stainless steel of a non-bearing structure, so that the train body weight can be greatly reduced, and the electric energy consumed by the subway train in the starting and running processes is reduced. The new energy automobile structurally adopts an aluminum-steel composite structure, so that the dead weight of the automobile body can be reduced, and the cruising ability is improved. Welding techniques are the primary choice for manufacturing aluminum and steel composite structures. However, because the solid solubility between steel and aluminum is low, the thermal physical properties such as melting point, density, thermal conductivity, linear expansion coefficient, lattice constant and the like have large differences, and the steel and the aluminum are easy to react to generate brittle intermetallic compounds, and in addition, welding defects such as air holes, inclusions, cracks and the like are easy to generate in the welding process, so that the mechanical properties of the joint are weakened. The above factors limit the application of the stainless steel-aluminum alloy dissimilar metal structural member. In order to obtain a superior aluminum-steel dissimilar joint, researchers have introduced alloying elements to participate in interfacial reactions by using materials (intermediate layers, filler metals, coatings, or combinations thereof) to regulate the interfacial layer. However, the addition of welding wire, plating or pre-alloying powder increases the complexity of the welding process and reduces the welding efficiency.
The aluminum steel dissimilar metal lap joint is connected by using the fusion brazing, so that the complexity of the welding process is reduced, and the welding efficiency is improved. The laser melting brazing has the advantages of small heat input amount, easily controlled heat source, high efficiency, strong accessibility and the like, is an ideal choice for realizing the high-efficiency connection of the aluminum alloy/steel composite structure at present, and can obtain the lap joint welding joint with the strength of more than 200N/mm by the laser self-melting brazing in the prior art. However, the existing laser welding and brazing of the aluminum alloy/steel composite structure still has the problems of uneven structure of an aluminum alloy/steel composite joint, low connection strength of a joint surface, easy generation of hot cracks and the like, and can not meet the requirements of the existing stainless steel-aluminum alloy welding quality and production efficiency to a certain extent.
Disclosure of Invention
The invention aims to provide a method for welding aluminum alloy and stainless steel capable of obtaining a high-strength welding joint, which adopts a variable power pulse laser beam and a variable polarity pulse arc as a composite heat source for welding and can obtain the high-strength welding joint with excellent comprehensive performance.
The invention adopts the technical scheme that the invention achieves the aim that: a welding method of aluminum alloy and stainless steel capable of obtaining a high-strength welding joint comprises the steps of respectively polishing and cleaning areas to be welded of an aluminum alloy plate and a stainless steel plate to be welded; assembling the aluminum alloy plate into a lap joint mode with the aluminum alloy plate on the upper part and the stainless steel on the lower part to form a workpiece to be welded, welding the workpiece to be welded by adopting a laser beam-electric arc composite welding heat source, melting the aluminum alloy by the composite welding heat source, heating but not melting the stainless steel, and spreading the molten aluminum alloy on the unmelted stainless steel to form a brazing interface;
the laser beam-electric arc composite welding heat source comprises a variable power pulse laser beam and a variable polarity pulse electric arc, the variable power pulse laser beam and the variable polarity pulse electric arc jointly act on a workpiece to be welded to form a welding pool, and the variable power pulse laser beam comprises a high-power laser pulse and a low-power laser pulse with the average power ratio of 1.5-2; the variable polarity pulse arc comprises a positive polarity pulse arc and a reverse polarity pulse arc with the average power ratio of 2-4;
the variable power pulse laser beam and the variable polarity pulse arc are modulated by synchronous pulses, the pulse frequency is recorded as f, and the f is 80Hz-120 Hz; the power change of the variable power pulse laser beam and the polarity transition of the variable polarity pulse arc are synchronous, namely the power change frequency of the variable power pulse laser beam is the same as the polarity transition frequency of the variable polarity pulse arc, and is recorded as f ', f' is 1/6f-1/3 f; the positive polarity pulse arc is synchronous with the high-power laser pulse, and the reverse polarity pulse arc is synchronous with the low-power laser pulse;
before welding, adjusting the position of a variable polarity pulse arc welding gun to ensure that when the variable polarity pulse arc welding gun arcs, the arc heat of 2/3-3/4 acts on an aluminum alloy plate, the arc heat of 1/3-1/4 acts on a stainless steel plate, and a variable power pulse laser beam is positioned on the front side of the variable polarity pulse arc welding gun along the welding direction;
in the welding process, the variable power pulse laser beam and the variable polarity pulse arc welding gun synchronously move forwards along the welding direction, wherein the moving speed is v, and v is (1/4f '-1/3 f') mm/s; while the variable power pulse laser beam advances forwards along the welding direction, the laser spot on the surface of the workpiece to be welded swings along the direction vertical to the welding seam, the swinging frequency is f ', f' -1/4 f '-1/2 f', and the average heat distribution of the swinging variable power pulse laser beam on the workpiece to be welded in the welding process is as follows by adjusting the position of the swinging central shaft and the swinging amplitude: 2/3-3/4 laser heat is irradiated on the aluminum alloy plate, and 1/3-1/4 laser heat is irradiated on the stainless steel plate; in the swinging process, the polarized pulse arc welding gun only moves forwards along the welding direction, and does not move in other directions, and the electric arc swings in a small range under the induction of the swinging laser beam.
Compared with the prior art, the invention has the beneficial effects that:
firstly, the welding is carried out by adopting a composite mode of taking the electric arc and the laser as a composite heat source, the respective advantages of two independent heat sources of the laser and the electric arc are combined, the defects of the two heat sources are greatly avoided, the energy utilization rate and the welding speed are improved, the welding seam forming is improved, and the high-quality welding joint is favorably obtained. The laser beam is arranged on the front side of the electric arc along the welding direction, and plays a role in drawing the electric arc, reducing electric arc resistance, preventing arc root from drifting and ensuring high-speed stable welding of the electric arc.
And secondly, the electric arc adopts polarity-variable pulse electric arc, so that the cathode cleaning effect can be exerted to remove the oxide film with a compact surface, the electrode burning loss can be reduced and the shape of the electrode tip can be kept under the precondition that the aluminum alloy surface oxide film cleaning effect and the electric arc stability are ensured. The laser beam adopts a variable power pulse laser beam, the high power laser pulse is synchronous with the positive polarity pulse arc to form a high power welding heat source, the low power laser pulse is synchronous with the reverse polarity pulse arc to form a low power welding heat source, the high power welding heat source is matched with the low power welding heat source to form a low frequency pulse heat source, the pulse heat source can obtain a well-formed welding joint through smaller heat input, the heat effect range is small, the generation of an excessively thick brittle intermetallic compound is reduced, microcracks caused by the excessively large thickness of the intermetallic compound are avoided, and the quality of the welding joint is ensured.
And thirdly, the variable power pulse laser beam and the variable polarity pulse arc adopt synchronous pulse modulation, and experiments prove that the synchronous pulse modulation can prevent metal from overheating, is beneficial to refining weld grains and improves the mechanical property of the joint.
And fourthly, the variable power pulse laser beam swings in the direction perpendicular to the welding line in the welding process, meanwhile, the electric arc is induced to swing, the energy distribution of the laser on the aluminum alloy and the stainless steel plate can be accurately adjusted, the aluminum alloy is melted, the stainless steel is not melted, the melted aluminum alloy is spread on the unmelted stainless steel to form a stable and uniform brazing interface, meanwhile, the small heat input blocks the generation of the over-thick brittle intermetallic compound, the microcrack caused by the overlarge thickness of the intermetallic compound is avoided, and the quality of a welding joint is ensured.
Fifthly, the interface temperature distribution can be more uniform due to the swinging laser beam and the electric arc, the thickness and the components of intermetallic compounds formed at different positions of the interface are similar, and the uniform fusion-brazing joint of the interface layer can be obtained. Moreover, the swinging of the laser beam and the electric arc not only enables the heat to be more uniform, but also enables the swinging laser beam and the electric arc to generate obvious stirring effect on a molten pool, improves the wettability of the joint, reduces welding pores, and accordingly obtains the welding and soldering joint with excellent performance and uniform interface layer.
And sixthly, the high-strength welding joint with good forming and less defects can be obtained through coupling matching between the pulse frequency of the variable power pulse laser beam and the variable polarity pulse arc, the power change frequency of the variable power pulse laser beam, the polarity conversion frequency of the variable polarity pulse arc, the swing frequency of the variable power pulse laser beam and the welding speed and through smaller heat input.
In a word, the invention adopts the variable power pulse laser beam and the variable polarity pulse arc as the composite heat source, the two adopt synchronous pulse modulation, the high power laser pulse is synchronous with the positive polarity pulse arc, the low power laser pulse is synchronous with the reverse polarity pulse arc, the variable power pulse laser beam swings in the welding process and induces the electric arc to swing, so as to accurately control the distribution of the welding heat source on the stainless steel plate and the aluminum alloy plate, and finally obtain the welding joint with the intensity of more than 300N/mm by combining the coordination among the pulse frequency, the laser power change frequency, the electric arc polarity change frequency, the swing frequency and the welding speed.
Further, after polishing and cleaning the areas to be welded of the aluminum alloy plate and the stainless steel plate to be welded, before forming a lap-joint workpiece to be welded, the areas to be welded of the stainless steel plate are subjected to surface activation treatment by using a pickling solution, and a Cu metal plating layer with the thickness of 5-8 μm and an Ag metal plating layer with the thickness of 5-9 μm are sequentially plated on the surfaces of the areas to be welded of the stainless steel plate in a brush plating manner, so that a Cu-Ag composite plating layer is formed on the surfaces of the areas to be welded of the stainless steel plate.
Firstly, the acid pickling activation is carried out on the to-be-welded area of the stainless steel plate, not only is the surface oxide film further removed, but also the activation points are generated on the surface of the stainless steel, the deposition efficiency and the adhesive force of the coating on the surface of the stainless steel are improved, the Cu-Ag composite coating prepared on the surface of the stainless steel is adopted for alloy element interface regulation, the thickness of the alloy element layer can be randomly controlled compared with the thickness of the alloy element layer added in an intermediate layer, a strict assembly flow is not needed, the adhesion is stronger compared with a common metal powder coating, the types and the proportions of the total elements can be randomly controlled compared with the introduction of the alloy elements into a welding wire, and the interference of other irrelevant elements is avoided. The Cu-Ag composite coating on the surface of the stainless steel can promote the molten aluminum alloy to spread on the surface of the stainless steel, reduce the wetting angle and obtain the welding joint with attractive appearance. Cu and Ag elements in the Cu-Ag composite coating can participate in Fe-Al metallurgical reaction to replace Fe atoms in an Fe-Al compound, so that the brittleness of the intermetallic compound is reduced, the chemical potential of the Fe elements at an aluminum alloy-stainless steel interface is improved, the Fe atoms are prevented from diffusing into molten aluminum alloy, the intermetallic compound is prevented from being too thick, microcracks are avoided, and the comprehensive mechanical property of a welding joint is improved.
Furthermore, the diameter of a laser spot of the variable power pulse laser beam on the surface of the workpiece to be welded is 1mm-3mm, the swing amplitude of swing in the welding process is 1mm-3mm, and the distance between the intersection point of the central axis of the variable power pulse laser beam and the surface of the workpiece to be welded and the intersection point of the central axis of the variable polarity pulse arc electrode and the surface of the workpiece to be welded is 2mm-3 mm.
Furthermore, the average power ratio of the high-power laser pulse to the positive polarity pulse arc is 0.6-1.5, and the average power ratio of the low-power laser pulse to the reverse polarity pulse arc is 1.3-2.
Furthermore, in the polarity-variable pulse arc, the ratio of the action time of the positive polarity pulse arc to the action time of the reverse polarity pulse arc is 1.5-3 in one polarity conversion period.
Furthermore, the average power of the high-power laser pulse in the variable-power pulse laser beam is 1500w-2200w, the average power of the low-power laser pulse is 800w-1400w, the average power of the positive polarity pulse arc in the variable polarity pulse arc is 1500w-2200w, and the average power of the reverse polarity pulse arc is 400w-800 w.
Tests prove that the power ratio, the ratio of the action time of the positive-polarity pulse arc to the action time of the reverse-polarity pulse arc and the power ranges of the variable-power pulse laser beam and the variable-polarity pulse arc are all favorable for spreading the aluminum alloy on the surface of the stainless steel to form a well-formed welding joint, and simultaneously, the growth of intermetallic compounds can be controlled, the thickness of the brittle and hard intermetallic compounds is controlled, and the high-strength welding joint is obtained.
In the invention, the total heat quantity of the welding heat source is determined according to the type and the thickness of the welding plate, and tests prove that after the total heat quantity of the welding heat source is determined, the welding heat source is distributed according to the power ratio of the invention, thereby being beneficial to obtaining a welding joint with excellent comprehensive performance.
Furthermore, the laser beam-electric arc composite welding heat source also comprises a scanning laser beam, wherein the scanning laser beam is positioned on the rear side of the variable polarity pulse electric arc welding gun along the welding direction, and the distance between the intersection point of the central axis of the scanning laser beam and the surface of the workpiece to be welded and the intersection point of the central axis of the variable polarity pulse electric arc electrode and the surface of the workpiece to be welded is 10-15 mm; in the welding process, the scanning laser beam and the variable polarity pulse arc welding gun synchronously move forwards along the welding direction; the scanning laser beam rotationally scans the surface of the weld joint while advancing in the welding direction, and the scanning range covers the weld joint area.
The aluminum alloy has high linear expansion coefficient, large volume shrinkage during solidification, high solubility to hydrogen, high laser beam-electric arc composite welding speed, short existing time of a molten pool, high cooling speed, and the weld metal easily generates defects such as air hole defect, crack layering and the like due to the over-quick solidification. Moreover, the scanning laser beam can also properly soften the welding joint, so that the strength and the plasticity of the welding joint can be matched.
Furthermore, the ratio of the power of the scanning laser beam to the power of the high-power laser pulse in the variable power pulse laser beam is 0.3-0.6, and the scanning frequency of the scanning laser beam is 80Hz-300 Hz.
Tests prove that the scanning laser beam with the power ratio and the scanning frequency is beneficial to playing the role of the scanning laser beam, reducing the defects of air holes, deformation and the like, and obtaining the formed attractive welding line while ensuring the purity of the welding line.
Furthermore, the scanning laser beam rotationally scans on the surface of the welding seam, and the specific mode that the scanning range covers the welding seam area is as follows: the laser focus of the scanning laser beam is controlled to rotate in the direction parallel to the surface of the welding workpiece, and meanwhile, the scanning laser beam reciprocates in the direction vertical to the surface of the welding workpiece, the frequency of the rotating motion is the same as that of the reciprocating motion, so that the scanning path of the laser focus of the scanning laser beam is parallel to the surface of the welding seam, and the scanning range of a laser spot irradiated on the surface of the welding seam just covers the surface of a welding seam area by adjusting the rotating radius. The diameter of the laser focus rotating in the direction parallel to the surface of the welding workpiece is the diameter of the welding seam minus the diameter of the laser spot of the scanning laser beam on the surface of the welding seam, and the amplitude of the laser focus reciprocating in the direction perpendicular to the surface of the welding workpiece is the height of the welding seam, so that the scanning range of the laser spot of the scanning laser beam irradiating on the surface of the welding seam just covers the surface of the welding seam area.
The laser focus of the scanning laser beam rotates in the direction parallel to the surface of the welding workpiece and is generated by the rotation of the wedge-shaped mirror, the laser focus of the scanning laser beam reciprocates in the direction vertical to the surface of the welding workpiece and is realized by the liquid drop lens with curvature deformation under different electric field strengths along with the change of the electric field strength, the liquid drop lens and the wedge-shaped mirror are concentrically arranged, and the central axis of the liquid drop lens is kept concentric with the wedge-shaped mirror all the time in the laser beam scanning process.
Furthermore, the average power of the high-power laser pulse in the variable-power pulse laser beam is 1300w-2000w, the average power of the low-power laser pulse is 600w-1200w, the average power of the positive polarity pulse arc in the variable polarity pulse arc is 1300w-2000w, the average power of the reverse polarity pulse arc is 200w-600w, and the power of the scanning laser beam is 400w-1000 w.
Tests prove that the variable power pulse laser beam, the variable polarity pulse arc and the scanning laser beam in the power range are adopted for welding, so that the aluminum alloy can be ensured to spread on the surface of the stainless steel to form a well-formed welding joint, the growth of intermetallic compounds can be controlled, the thickness of the brittle and hard intermetallic compounds is controlled, welding defects such as air holes and welding deformation are reduced, and a high-strength welding joint is obtained.
Drawings
FIG. 1 is a schematic diagram of a composite welding three-dimensional structure using a variable power pulse laser beam and a variable polarity pulse arc as a welding heat source according to the present invention.
FIG. 2 is a schematic diagram of the laser spot of a variable power pulsed laser beam according to the present invention in the weaving path during welding.
FIG. 3 is a schematic diagram of the output power waveform of the variable power pulse laser beam and the output current waveform of the variable polarity pulse arc according to the present invention.
FIG. 4 is a schematic diagram of a composite welding three-dimensional structure using a variable power pulse laser beam, a variable polarity pulse arc and a scanning laser beam as welding heat sources.
In the figure, 1 is a variable polarity pulse arc welding gun, 2 is an electric arc generated by the variable polarity pulse arc welding gun, 3 is a variable power pulse laser beam, 4 is a laser spot swing path of the variable power pulse laser beam, 5 is a scanning laser beam, 6 is a scanning path of the scanning laser beam, 7 is an aluminum alloy plate, 8 is a stainless steel plate, 9 is a welding seam, 10 is a laser spot of the variable power pulse laser beam, 11 is a swing central axis of the variable power pulse laser beam, and theta is1Is the included angle theta between the central axis of the pulse laser beam with variable power and the vertical direction2Is the angle between the central axis of the scanning laser beam and the vertical direction.
Detailed Description
Examples
A welding method of aluminum alloy and stainless steel capable of obtaining a high-strength welding joint comprises the steps of respectively polishing and cleaning areas to be welded of an aluminum alloy plate and a stainless steel plate to be welded; assembling the aluminum alloy plate into a lap joint mode with the aluminum alloy plate on the upper part and the stainless steel on the lower part to form a workpiece to be welded, welding the workpiece to be welded by adopting a laser beam-electric arc composite welding heat source, melting the aluminum alloy by the composite welding heat source, heating but not melting the stainless steel, and spreading the molten aluminum alloy on the unmelted stainless steel to form a brazing interface;
the laser beam-electric arc composite welding heat source comprises a variable power pulse laser beam and a variable polarity pulse electric arc, the variable power pulse laser beam and the variable polarity pulse electric arc jointly act on a workpiece to be welded to form a welding pool, and the variable power pulse laser beam comprises a high-power laser pulse and a low-power laser pulse with the average power ratio of 1.5-2; the variable polarity pulse arc comprises a positive polarity pulse arc and a reverse polarity pulse arc with the average power ratio of 2-4; the average power ratio of the high-power laser pulse to the positive-polarity pulse arc is preferably 0.6-1.5, and the average power ratio of the low-power laser pulse to the reverse-polarity pulse arc is preferably 1.3-2;
the variable power pulse laser beam and the variable polarity pulse arc are modulated by synchronous pulses, the pulse frequency is recorded as f, and the f is 80Hz-120 Hz; the power change of the variable power pulse laser beam and the polarity transition of the variable polarity pulse arc are synchronous, namely the power change frequency of the variable power pulse laser beam is the same as the polarity transition frequency of the variable polarity pulse arc, and is recorded as f ', f' is 1/6f-1/3 f; the positive polarity pulse arc is synchronous with the high-power laser pulse, and the reverse polarity pulse arc is synchronous with the low-power laser pulse; in a polarity conversion period of the variable polarity pulse arc, the ratio of the action time of the positive polarity pulse arc to the action time of the reverse polarity pulse arc is preferably 1.5-3;
FIG. 3 is a schematic diagram of the output power waveform of the variable power pulse laser beam and the output current waveform of the variable polarity pulse arc according to the present invention. In the figure I1Is the average current of a positive polarity pulsed arc, I2Average current, P, of a pulsed arc of opposite polarity1Is the average power, P, of the high power laser pulses2For average power of low power laser pulses, DCEP indicates dc positive and DCEN indicates dc negative. In the welding process, the variable polarity pulse arc adjusts and monitors the welding voltage in real time through the arc length tracker, and the welding voltage maintains the welding voltage of the arc unchanged, so the average power change of the pulse arc is synchronous with the average current change of the pulse arc. Fig. 3 is a schematic diagram for representing the synchronization of the power change of the variable power pulse laser beam and the polarity transition of the variable polarity pulse arc, and the power pulse frequency of the variable power pulse laser beam and the current pulse frequency of the variable polarity pulse arc are represented to be different from the actual pulse frequency.
Before welding, adjusting the position of a variable polarity pulse arc welding gun to ensure that when the variable polarity pulse arc welding gun arcs, the arc heat of 2/3-3/4 acts on an aluminum alloy plate, the arc heat of 1/3-1/4 acts on a stainless steel plate, and a variable power pulse laser beam is positioned on the front side of the variable polarity pulse arc welding gun along the welding direction; FIG. 1 is a schematic diagram of a composite welding three-dimensional structure using a variable power pulse laser beam and a variable polarity pulse arc as a welding heat source according to the present invention.
In the welding process, the variable power pulse laser beam and the variable polarity pulse arc welding gun synchronously move forwards along the welding direction, wherein the moving speed is v, and v is (1/4f '-1/3 f') mm/s; while the variable power pulse laser beam advances forwards along the welding direction, the laser spot on the surface of the workpiece to be welded swings along the direction vertical to the welding seam, the swinging frequency is f ', f' -1/4 f '-1/2 f', and the average heat distribution of the swinging variable power pulse laser beam on the workpiece to be welded in the welding process is as follows by adjusting the position of the swinging central shaft and the swinging amplitude: 2/3-3/4 laser heat is irradiated on the aluminum alloy plate, and 1/3-1/4 laser heat is irradiated on the stainless steel plate; in the swinging process, the polarized pulse arc welding gun only moves forwards along the welding direction, and does not move in other directions, and the electric arc swings in a small range under the induction of the swinging laser beam.
FIG. 2 is a schematic diagram of the laser spot of a variable power pulsed laser beam according to the present invention in the weaving path during welding. In the figure, a laser spot 10 is a schematic diagram of the position of a laser spot irradiated by a variable power pulse laser beam on a workpiece to be welded when welding starts. In the welding process, laser spots of laser beams on the surface of a workpiece to be welded swing along the direction vertical to a welding seam by taking 11 as a swing central axis.
Preferably, after polishing and cleaning the areas to be welded of the aluminum alloy plate and the stainless steel plate to be welded and before forming the workpieces to be welded in a lap joint manner, the areas to be welded of the stainless steel plate are subjected to surface activation treatment by using a pickling solution, and a Cu metal plating layer with the thickness of 5-8 μm and an Ag metal plating layer with the thickness of 5-9 μm are sequentially plated on the surfaces of the areas to be welded of the stainless steel plate in a brush plating manner, so that a Cu-Ag composite plating layer is formed on the surfaces of the areas to be welded of the stainless steel plate.
Preferably, the diameter of a laser spot of the variable power pulse laser beam on the surface of the workpiece to be welded is 1mm-3mm, the swing amplitude of swing in the welding process is 1mm-3mm, and the distance between the intersection point of the central axis of the variable power pulse laser beam and the surface of the workpiece to be welded and the intersection point of the central axis of the variable polarity pulse arc electrode and the surface of the workpiece to be welded is 2mm-3 mm.
Preferably, the average power of the high-power laser pulse in the variable power pulse laser beam is 1500w-2200w, the average power of the low-power laser pulse is 800w-1400w, the average power of the positive polarity pulse arc in the variable polarity pulse arc is 1500w-2200w, and the average power of the reverse polarity pulse arc is 400w-800 w.
Preferably, the laser beam-electric arc hybrid welding heat source further comprises a scanning laser beam, the scanning laser beam is positioned on the rear side of the variable polarity pulse arc welding gun along the welding direction, and the distance between the intersection point of the central axis of the scanning laser beam and the surface of the workpiece to be welded and the intersection point of the central axis of the variable polarity pulse arc electrode and the surface of the workpiece to be welded is 10mm-15 mm; in the welding process, the scanning laser beam and the variable polarity pulse arc welding gun synchronously move forwards along the welding direction; the scanning laser beam rotationally scans the surface of the weld joint while advancing in the welding direction, and the scanning range covers the weld joint area. FIG. 4 is a schematic diagram of a composite welding three-dimensional structure using a variable power pulse laser beam, a variable polarity pulse arc and a scanning laser beam as welding heat sources. In the figure, 6 is a scanning path of the scanning laser beam, θ2The included angle between the central axis of the scanning laser beam and the vertical direction is preferably 5-15 degrees, and the laser spot diameter of the scanning laser beam on the surface of the welding seam is preferably 0.5mm-1 mm.
More preferably, the ratio of the power of the scanning laser beam to the power of the high-power laser pulse in the variable power pulse laser beam is 0.3-0.6, and the scanning frequency of the scanning laser beam is 80Hz-300 Hz.
More preferably, the scanning laser beam rotationally scans on the surface of the weld joint, and the specific way of covering the weld joint area by the scanning range is as follows: the laser focus of the scanning laser beam is controlled to rotate in the direction parallel to the surface of the welding workpiece, and meanwhile, the scanning laser beam reciprocates in the direction vertical to the surface of the welding workpiece, the frequency of the rotating motion is the same as that of the reciprocating motion, so that the scanning path of the laser focus of the scanning laser beam is parallel to the surface of the welding seam, and the scanning range of a laser spot irradiated on the surface of the welding seam just covers the surface of a welding seam area by adjusting the rotating radius. The laser focus of the scanning laser beam rotates in the direction parallel to the surface of the welding workpiece and is generated by the rotation of the wedge-shaped mirror, the laser focus of the scanning laser beam reciprocates in the direction vertical to the surface of the welding workpiece and is realized by the liquid drop lens with curvature deformation under different electric field strengths along with the change of the electric field strength, the liquid drop lens and the wedge-shaped mirror are concentrically arranged, and the central axis of the liquid drop lens is kept concentric with the wedge-shaped mirror all the time in the laser beam scanning process.
In the case that the laser beam-arc hybrid welding heat source comprises a scanning laser beam, a variable power pulse laser beam and a variable polarity pulse arc, preferably, the average power of high power laser pulses in the variable power pulse laser beam is 1300w-2000w, the average power of low power laser pulses is 600w-1200w, the average power of positive polarity pulse arc in the variable polarity pulse arc is 1300w-2000w, the average power of reverse polarity pulse arc is 200w-600w, and the power of the scanning laser beam is 400w-1000 w.
Example one
A can obtain the welding method of aluminum alloy and stainless steel of the high-strength welded joint, the said aluminum alloy plate to be welded is 6061 aluminum alloy plate with thickness of 2mm, the stainless steel plate to be welded is 301L stainless steel plate with thickness of 2mm, the welding method includes treating the area to be welded of aluminum alloy plate and stainless steel plate to polish and wash separately; the assembly is in a lap joint mode that an aluminum alloy plate is arranged above and below stainless steel, the lap joint distance is set to be 8mm, a workpiece to be welded is formed, the workpiece to be welded is welded by adopting a laser beam-electric arc composite welding heat source, the aluminum alloy is melted by the composite welding heat source, the stainless steel is heated but not melted, the melted aluminum alloy is spread on the unmelted stainless steel to form a brazing interface, and the flow of argon gas used for high-purity argon gas protection is 25L/min in the welding process;
the laser beam-electric arc composite welding heat source comprises a variable power pulse laser beam and a variable polarity pulse electric arc, the variable power pulse laser beam and the variable polarity pulse electric arc jointly act on a workpiece to be welded to form a welding pool, and the variable power pulse laser beam comprises a high-power laser pulse and a low-power laser pulse; the polarity-variable pulse electric arc comprises a positive polarity pulse electric arc and a reverse polarity pulse electric arc;
the variable power pulse laser beam and the variable polarity pulse arc are modulated by synchronous pulses, the pulse frequency is recorded as f, the f is 100Hz, and the pulse duty ratio is 50 percent; the power change of the variable power pulse laser beam and the polarity transition of the variable polarity pulse arc are synchronous, namely the power change frequency of the variable power pulse laser beam is the same as the polarity transition frequency of the variable polarity pulse arc, and is recorded as f', f is 25 Hz; the positive polarity pulse arc is synchronous with the high-power laser pulse, and the reverse polarity pulse arc is synchronous with the low-power laser pulse; in a polarity conversion period, the action time of the positive polarity pulse arc is 25ms, and the action time of the reverse polarity pulse arc is 15 ms;
before welding, adjusting the position of a variable polarity pulse arc welding gun to ensure that when the variable polarity pulse arc welding gun arcs, the arc heat of 3/4 acts on an aluminum alloy plate, the arc heat of 1/4 acts on a stainless steel plate, a variable power pulse laser beam is positioned on the front side of the variable polarity pulse arc welding gun along the welding direction and forms an included angle of 10 degrees with the vertical direction, and the projection of the central axis of the variable power pulse laser beam on the surface of a workpiece to be welded is parallel to the direction of a welding line;
in the welding process, the variable power pulse laser beam and the variable polarity pulse arc welding gun synchronously move forwards along the welding direction, wherein the moving speed is v, and v is 7 mm/s; the laser spot on the surface of the workpiece to be welded swings in the direction perpendicular to the welding seam while the variable power pulse laser beam advances forwards along the welding direction, the swinging frequency is f ", and f ═ 8Hz, and the average heat distribution of the swinging variable power pulse laser beam on the workpiece to be welded in the welding process is as follows by adjusting the position of the swinging central shaft and the swinging amplitude: 3/4 laser heat is irradiated on the aluminum alloy plate, 1/4 laser heat is irradiated on the stainless steel plate; in the swinging process, the polarized pulse arc welding gun only moves forwards along the welding direction, and does not move in other directions, and the electric arc swings in a small range under the induction of the swinging laser beam.
In the embodiment, the variable polarity pulse arc welding gun is arranged perpendicular to the surface of the workpiece to be welded, and the distance between the intersection point of the central axis of the variable power pulse laser beam and the surface of the workpiece to be welded and the intersection point of the central axis of the variable polarity pulse arc electrode and the surface of the workpiece to be welded is 3 mm.
In this example, the laser spot diameter of the variable power pulse laser beam on the surface of the workpiece to be welded is 2mm, and the swing amplitude of the laser beam swinging on the surface of the workpiece to be welded is 2 mm.
In the example, the average power of high-power laser pulses in the variable-power pulse laser beam is 1900w, the average power of low-power laser pulses is 1100w, the average current of positive polarity pulse arcs in the variable polarity pulse arcs is 120A, the average current of reverse polarity pulse arcs in the variable polarity pulse arcs is 40A, and the welding voltage is adjusted and monitored in real time through an arc length tracker during the welding process, so that the welding voltage is maintained at about 16V.
By analyzing the mechanical properties of the welding joint, the average strength of the welding joint obtained by the welding method of the embodiment is up to 321N/mm, which is far higher than that of the existing laser self-fluxing brazing method.
Example two
The present embodiment is substantially the same as the first embodiment, except that the present embodiment uses a pickling solution to perform surface activation treatment on the to-be-welded area of the stainless steel plate after polishing and cleaning the to-be-welded area of the aluminum alloy plate and the stainless steel plate to be welded, and uses a brush plating method to sequentially plate a Cu metal plating layer with a thickness of 7 μm and an Ag metal plating layer with a thickness of 7 μm on the to-be-welded area of the stainless steel plate, and forms a Cu-Ag composite plating layer on the to-be-welded area of the stainless steel plate, before forming a to-be-welded workpiece in a lap joint form.
By analyzing the mechanical properties of the welding joint, the average strength of the welding joint obtained by the welding method of the embodiment is as high as 332N/mm, which is far higher than that of the existing laser self-fluxing brazing method.
EXAMPLE III
A can obtain the welding method of aluminum alloy and stainless steel of the high-strength welded joint, the said aluminum alloy plate to be welded is 6061 aluminum alloy plate with thickness of 2mm, the stainless steel plate to be welded is 301L stainless steel plate with thickness of 2mm, the welding method includes treating the area to be welded of aluminum alloy plate and stainless steel plate to polish and wash separately; the assembly is in a lap joint mode that an aluminum alloy plate is arranged above and below stainless steel, the lap joint distance is set to be 8mm, a workpiece to be welded is formed, the workpiece to be welded is welded by adopting a laser beam-electric arc composite welding heat source, the aluminum alloy is melted by the composite welding heat source, the stainless steel is heated but not melted, the melted aluminum alloy is spread on the unmelted stainless steel to form a brazing interface, and the flow of argon gas used for high-purity argon gas protection is 25L/min in the welding process;
the laser beam-electric arc composite welding heat source comprises a variable power pulse laser beam, a variable polarity pulse electric arc and a scanning laser beam, wherein the power pulse laser beam and the variable polarity pulse electric arc jointly act on a workpiece to be welded to form a welding molten pool, and the variable power pulse laser beam comprises a high-power laser pulse and a low-power laser pulse; the polarity-variable pulse electric arc comprises a positive polarity pulse electric arc and a reverse polarity pulse electric arc;
the variable power pulse laser beam and the variable polarity pulse arc are modulated by synchronous pulses, the pulse frequency is recorded as f, the f is 100Hz, and the pulse duty ratio is 50 percent; the power change of the variable power pulse laser beam and the polarity transition of the variable polarity pulse arc are synchronous, namely the power change frequency of the variable power pulse laser beam is the same as the polarity transition frequency of the variable polarity pulse arc, and is recorded as f', f is 25 Hz; the positive polarity pulse arc is synchronous with the high-power laser pulse, and the reverse polarity pulse arc is synchronous with the low-power laser pulse; in a polarity conversion period, the action time of the positive polarity pulse arc is 25ms, and the action time of the reverse polarity pulse arc is 15 ms;
before welding, adjusting the position of a variable polarity pulse arc welding gun to ensure that when the variable polarity pulse arc welding gun arcs, the arc heat of 3/4 acts on an aluminum alloy plate, the arc heat of 1/4 acts on a stainless steel plate, a variable power pulse laser beam is positioned on the front side of the variable polarity pulse arc welding gun along the welding direction and forms an included angle of 10 degrees with the vertical direction, a scanning laser beam is positioned on the rear side of the variable polarity pulse arc welding gun along the welding direction, and the projections of the central axes of the variable power pulse laser beam and the scanning laser beam on the surface of a workpiece to be welded are parallel to the welding line direction;
in the welding process, the variable power pulse laser beam and the variable polarity pulse arc welding gun synchronously move forwards along the welding direction, wherein the moving speed is v, and v is 7 mm/s; the laser spot on the surface of the workpiece to be welded swings in the direction perpendicular to the welding seam while the variable power pulse laser beam advances forwards along the welding direction, the swinging frequency is f ", and f ═ 8Hz, and the average heat distribution of the swinging variable power pulse laser beam on the workpiece to be welded in the welding process is as follows by adjusting the position of the swinging central shaft and the swinging amplitude: 3/4 laser heat is irradiated on the aluminum alloy plate, 1/4 laser heat is irradiated on the stainless steel plate; in the swinging process, the variable polarity pulse arc welding gun only moves forwards along the welding direction, and does not move in other directions, and the electric arc swings in a small range under the induction of the swinging laser beam; in the welding process, the scanning laser beam and the variable polarity pulse arc welding gun synchronously move forwards along the welding direction; the scanning laser beam rotationally scans the surface of the welding seam while advancing forwards along the welding direction, the scanning frequency is 200Hz, the scanning range covers the welding seam area, the included angle between the central axis of the scanning laser beam and the vertical direction is 10 degrees, and the laser spot diameter of the scanning laser beam on the surface of the welding seam is preferably 0.5 mm.
In the embodiment, the variable polarity pulse arc welding gun is arranged perpendicular to the surface of the workpiece to be welded, the distance between the intersection point of the central axis of the variable power pulse laser beam and the surface of the workpiece to be welded and the intersection point of the central axis of the variable polarity pulse arc electrode and the surface of the workpiece to be welded is 3mm, and the distance between the intersection point of the central axis of the scanning laser beam and the surface of the workpiece to be welded and the intersection point of the central axis of the variable polarity pulse arc electrode and the surface of the workpiece to be welded is 12 mm;
in this example, the laser spot diameter of the variable power pulse laser beam on the surface of the workpiece to be welded is 2mm, and the swing amplitude of the laser beam swinging on the surface of the workpiece to be welded is 2 mm.
In this example, the scanning laser beam rotationally scans on the surface of the weld joint, and the specific way of covering the weld joint area by the scanning range is as follows: the laser focus of the scanning laser beam is controlled to rotate in the direction parallel to the surface of the welding workpiece, and meanwhile, the scanning laser beam reciprocates in the direction vertical to the surface of the welding workpiece, the frequency of the rotating motion is the same as that of the reciprocating motion, so that the scanning path of the laser focus of the scanning laser beam is parallel to the surface of the welding seam, and the scanning range of a laser spot irradiated on the surface of the welding seam just covers the surface of a welding seam area by adjusting the rotating radius. The laser focus of the scanning laser beam rotates in the direction parallel to the surface of the welding workpiece and is generated by the rotation of the wedge-shaped mirror, the laser focus of the scanning laser beam reciprocates in the direction vertical to the surface of the welding workpiece and is realized by the liquid drop lens with curvature deformation under different electric field strengths along with the change of the electric field strength, the liquid drop lens and the wedge-shaped mirror are concentrically arranged, and the central axis of the liquid drop lens is kept concentric with the wedge-shaped mirror all the time in the laser beam scanning process.
In the example, the average power of high-power laser pulses in the variable-power pulse laser beam is 1700w, the average power of low-power laser pulses is 900w, the power of the scanning laser beam is 700w, the average current of positive polarity pulse arcs in the variable polarity pulse arcs is 100A, the average current of reverse polarity pulse arcs is 30A, and the welding voltage is adjusted and monitored in real time by an arc length tracker during welding so that the welding voltage is maintained at about 16V.
By analyzing the mechanical properties of the welding joint, the average strength of the welding joint obtained by the welding method of the embodiment is up to 328N/mm, which is far higher than that of the existing laser self-fluxing brazing method.