CN108406093B - Ultrafast laser difference micro-nano texture method for metal welding head - Google Patents
Ultrafast laser difference micro-nano texture method for metal welding head Download PDFInfo
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Abstract
The invention belongs to the technical field of laser micromachining, and particularly relates to an ultrafast laser difference micro-nano texture method of a metal welding head, which is a differential functional micro-nano texture technology based on an ultrafast laser accurate selection area and controllable morphology, takes ultrafast laser as an energy source, and carries out targeted functional micro-nano texture on phase components and microstructure of differences of different areas (a welding line area, a heat affected area and a base metal area) of the metal welding head, so as to realize surface modification and modification of the surface and end surface area of the welding head, and further improve the corrosion resistance and wear resistance of the surface and end area of the metal welding head.
Description
Technical Field
The invention belongs to the technical field of laser micro-machining, and particularly relates to an ultrafast laser difference micro-nano texture method for a metal welding head.
Background
The welding of metal materials is a manufacturing process and technology for joining the same or different metals in a heating, high-temperature or high-pressure mode and realizing permanent connection, and is widely applied to various fields such as aerospace, automobile manufacturing, ship manufacturing and the like. The metal welding method mainly comprises fusion welding, brazing, friction stir welding and the like. The fusion welding is that the local melting of the joint parts is caused by heating to form a molten pool, the joint parts are connected with each other after the molten pool is cooled and solidified, and in the fusion welding, other welding materials can be filled while the welding parts are heated according to the requirement to assist the welding. The main characteristic of brazing is that a metal material with a melting point lower than that of a welding part is used as a brazing filler metal, the brazing filler metal is heated to melt and wet a non-molten base metal, and meanwhile, the melted brazing filler metal is filled in a joint area and diffuses with the base metal mutually to realize welding. Friction stir welding is performed by rotating a cylindrical stirring head with a special shoulder and a pin boss at a high speed and slowly inserting the stirring head into a workpiece, plasticizing material in the vicinity of the stirring head by frictional heat generated by the stirring head and the material to be welded, transferring the plasticized metal material from the leading edge of the stirring head to the trailing edge of the stirring head while the stirring head is rotating and moving forward, and forming a solid phase joint by frictional heat generation and forging of the shoulder of the stirring head and the surface of the workpiece.
For the welding of metal materials, no matter what method is adopted, a joint area exists after welding, and the welded joint is divided into a weld joint area, a heat affected zone (the friction stir welding joint also has a thermomechanically affected zone) and a base metal area according to phase compositions and microstructure of different areas of the joint. Wherein, the change of welding seam district material shows to become solid-state recondensing crystallization from solid-state to liquid, and in the crystallization process, because the influence of welding heat effect, the crystalline grain of welding seam district is generally more tiny than the base metal district, and the welding seam center is generally for tiny isometric crystal, and the marginal crystalline grain growth direction of welding seam district becomes the column crystal along the opposite direction of heat current, and further, still can lead to the lattice distortion of welding seam district because the influence of heat effect, and simultaneously, crystalline grain especially grain boundary department generally has new precipitation phase for the chemical composition in welding seam district changes. Although the heat affected zone is always solid, the grains are enlarged due to the influence of heat, and new precipitated phases may exist in the grain interior and at the grain boundary. Finally, the base material region has a certain thermal effect but does not have any influence on the structure, chemical composition, etc. of the material. In short, the welded joint is a unique region of the same substrate with a differential microstructure, and the phase composition and microstructure of the material, such as chemical composition, texture crystal morphology (grain morphology and size, lattice distortion, etc.), precipitated phase composition and distribution, are different. Furthermore, the welding joint has complicated curves among the regions, and the regions are irregular. Due to the difference in phase composition and microstructure of each region, the corrosion resistance and wear resistance of the welded joint, particularly the heat affected zone, are weaker than those of the base material zone. Corrosion and wear are the main forms of material failure, and therefore, it is of great practical significance to develop methods for enhancing the corrosion and wear resistance of welded joints.
Disclosure of Invention
In order to solve the technical difficulties, the invention provides an ultrafast laser difference micro-nano texture method of a metal welding head, which takes ultrafast laser as an energy source, and selects the functional micro-nano texture of the ultrafast laser according to the difference phase components and microstructure of different areas (a welding seam area, a heat affected area and a base metal area) of the welding head, thereby realizing surface modification and modification of the surface and end surface area of the welding head and achieving the effects of corrosion resistance and abrasion resistance.
In order to achieve the purpose, the technical scheme of the invention is as follows: an ultrafast laser difference micro-nano texture method for a metal welding head comprises the following steps: (1) determining a weld joint area, a heat affected area and a base material area of the metal welding joint and differences of all areas in the phase components and the microstructure according to the measured phase components and the microstructure of the preprocessed metal welding joint;
(2) according to phase compositions and microstructure of each area of a welding line area, a heat affected area and a base material area, selecting ultrafast laser cross-scale micro-nano textures in a differentiated mode, and performing ultrafast laser texturing on the surfaces and/or end faces in each area of the welding line area, the heat affected area and the base material area so as to enable the tissue appearances of the surfaces and/or the end faces in each area of the welding line area, the heat affected area and the base material area to be uniform, and/or the crystal forms and the crystal grains to be uniform, and/or the crystal grains to be refined, and/or uniform mixed crystals to be formed, and/or distortion to be improved, and/or phase and phase compositions to be changed, so that the surface and/or end face tissues in each area of the welding line area, the heat affected area and the base material area are uniform, continuous and mutually dissolved.
The ultrafast laser cross-scale micro-nano texture comprises a single-cycle nano-ripple texture, a double-cycle nano-ripple texture, a micro-nano particle texture or a composite micro-nano texture and the like.
The composite micro-nano texture is composed of a plurality of unit textures which are arranged at intervals in a transverse, longitudinal, transverse and longitudinal vertical manner or in a transverse and longitudinal multi-angle mutually crossed manner and have adjustable sizes. The shape of the composite micro-nano texture comprises a dense slit shape, a square lattice shape, a hole shape, a circular pit shape, an orthogonal square column shape or a parallel grating shape and the like. The unit texture is in the shape of circle, ellipse, corrugated groove, linear groove or square.
The parameters of the ultrafast laser include: the pulse width is less than 12ps, the wavelength is 355-1064 nm, the power is 0-2W, and the repetition frequency is 1-100 KHz.
The method for measuring the phase composition and the microstructure of the metal welding head comprises the following steps: observing the surface appearance of the metal welding joint by using a metallographic microscope and/or a scanning electron microscope; analyzing chemical components of the metal welding head by using an EDX spectrometer carried by a scanning electron microscope; analytical testing of the phase structure and lattice parameters of metal solder joints was performed using transmission electron microscopy and/or X-ray diffractometry.
The surface topography comprises grain type, and/or grain size, and/or grain distribution.
The chemical composition analysis of the metal weld joint includes differential elemental content at grain boundaries and/or within grains.
The shapes of the surfaces and/or end faces in the welding seam area, the heat affected area and the base material area are planes or curved surfaces.
The pretreatment method of the metal welding head comprises the steps of polishing and cleaning in sequence, polishing to remove impurities, oxides and oil stains on the surface and the end part area of the metal welding head, and then cleaning with acetone. Specifically, a metal welding joint is polished by abrasive paper, and the abrasive paper is metallographic abrasive paper; the acetone cleaning mode is ultrasonic, and the acetone is washed by distilled water after ultrasonic treatment and dried for later use.
Compared with the prior art, the invention has the advantages that:
according to the method, the ultrafast laser is used as an energy source according to phase compositions and microstructure of the difference of different areas (a welding seam area, a heat affected area and a base metal area) of the metal welding head, the advantages of accurate area selection processing and shape controllable processing of the ultrafast laser micro-nano texture technology are fully utilized, different flat/curved surface areas of different types of metal welding heads are subjected to different functionalized surface textures, and the corrosion resistance and wear resistance of the areas (the welding seam area, the heat affected area and the base metal area) on the metal welding head are improved, so that the corrosion resistance and wear resistance of the whole metal welding head and the metal welding part are improved.
Drawings
FIG. 1 is a schematic view showing the distribution of a weld zone, a heat affected zone and a base metal zone of a metal welded joint. In the figure, A-weld zone, B-heat affected zone, C-parent metal zone.
FIG. 2 is a schematic diagram showing the distribution of weld zones, heat affected zones and base metal zones of different types of metal welding joints. In the figure, A-weld zone, B-heat affected zone, C-parent metal zone.
FIG. 3 is an electron microscope image and a schematic diagram of ultrafast laser micro-nano texture characteristics. FIG. 3(a) is an electron micrograph of ultrafast laser nanoscale-induced surface waviness and low-micron ablated hole structures: single-period nanometer ripples, double-period nanometer ripples and micro-nano particles; FIG. 3(b) is an electron microscope image (i.e., composite micro-nano texture) of an ultrafast laser ablation large-area micro-nano composite surface structure, which comprises dense seams, squares, holes, circular pits, orthogonal square columns and parallel gratings; FIG. 3(c) is a schematic diagram of a ultrafast laser ablation micron-sized large-area structure, including a micro-pore structure, a micro-groove structure and a cross structure, in which a is a distance between centers of two adjacent micro-pores in a horizontal axis direction, b is a distance between centers of two adjacent micro-pores in a vertical axis direction, and c is a diameter of the micro-pores; d is the distance between the central lines of two adjacent micro-grooves arranged along the direction of the transverse axis, and e is the width of the micro-groove; f is the distance between the central lines of two adjacent micro-grooves arranged along the direction of the transverse axis in the micro-groove cross arrangement structure, g is the width of the micro-grooves arranged along the direction of the transverse axis in the micro-groove cross arrangement structure, h is the distance between the central lines of two adjacent micro-grooves arranged along the direction of the longitudinal axis in the micro-groove cross arrangement structure, i is the width of the micro-grooves arranged along the direction of the longitudinal axis in the micro-groove cross arrangement structure, and a, b, c, d, e, f, g, h and i are variables.
Fig. 4 is a schematic diagram of ultrafast laser micro-nano texture of a welding head. In the figure, A-weld zone, B-heat affected zone, C-parent metal zone.
Detailed Description
The present invention will be further described with reference to the following drawings and examples, but the practice of the present invention is not limited to the following examples.
As shown in fig. 1 and 2, the metal welded joint is divided into a weld zone (a), a heat-affected zone (B), and a base material zone (C) according to differences in phase composition and microstructure of different regions of the metal welded joint, and the surface of the weld zone (a) is generally a curved surface, and the surfaces of the heat-affected zone (B) and the base material zone (C) are flat or curved surfaces. In the welding process, physical and chemical changes in the weld zone, the heat affected zone, and the base material zone of the metal welded joint are different, and the physical and chemical changes in the weld zone, the heat affected zone, and the base material zone are different from each other, and phase compositions and microstructure in the weld zone, the heat affected zone, and the base material zone are also different from each other, resulting in a decrease in corrosion resistance and wear resistance of the metal welded joint.
Laser light interacts with materials due to its good directivity, coherence and high energy density, and thus is widely used in the technical fields of material processing such as cutting, welding, surface treatment and drilling. The surface treatment by laser can be completed in a short time, and the tissue structure of the surface of the workpiece is changed to form a surface modification layer with a certain thickness; the laser treatment of the surface of the workpiece is selective, which is beneficial to pertinently improving the physical and mechanical properties of the surface of the workpiece, so that the whole workpiece keeps enough toughness and strength, the corrosion resistance and the abrasion resistance are improved, and higher and specific service performance is obtained.
The specific operation of the invention is as follows:
(1) selecting a metal welding part with a welding head and preprocessing the metal welding part, mainly comprising the steps of uniformly polishing the surface and the end part area of the welding head by using metallographic abrasive paper, and aiming at removing impurities such as oxide, oil stain and the like on the surface, then putting the metal welding part in acetone, cleaning the metal welding part by using ultrasonic waves, taking out the metal welding part, washing the metal welding part by using distilled water, and airing the metal welding part for later use.
(2) Observing the surface appearance of a welding joint area of the pretreated metal welding piece by using a metallographic microscope, wherein the surface appearance specifically comprises the type, size and distribution of crystal grains; observing the appearance of the welding head area by using a scanning electron microscope; analyzing chemical components of a welding head area by using an EDX spectrometer carried by a scanning electron microscope, and particularly paying attention to the content of differential elements in a crystal boundary and a crystal; and (4) carrying out analysis and test on the phase structure and the lattice parameters of the welding head area by using a transmission electron microscope and an X-ray diffractometer.
(3) From the measurements, the different zones of the weld joint, i.e. the weld zone, the heat affected zone and the base material zone, as well as the differences in phase composition and microstructure of the zones, are analyzed and determined.
(4) The different zones were cut and samples of each zone were prepared.
(5) And carrying out ultrafast laser surface micro-nano functional texture on the samples in all the areas, wherein basic parameters of ultrafast laser include pulse width less than 12ps, wavelength 355-1064 nm, power 0-2W and repetition frequency 1-100 KHz. And according to the specific texture morphology shown in fig. 3, adjusting the laser energy value, the ablation pulse number for irradiating a single micropore or the scanning speed and the scanning frequency during the ablation of the microgroove, and according to the space of the texture microstructure, adjusting the moving distance of the sample, and finally texturing different surface micro-nano structures shown in fig. 4 on the surface of the sample in each area.
FIG. 3(a) is an electron micrograph of ultrafast laser nanoscale-induced surface waviness and low-micron ablated hole structures: single-period nanometer ripples, double-period nanometer ripples and micro-nano particles; FIG. 3(b) is an electron microscope image (i.e., composite micro-nano texture) of an ultrafast laser ablation large-area micro-nano composite surface structure, which comprises dense seams, squares, holes, circular pits, orthogonal square columns and parallel gratings; FIG. 3(c) is a schematic diagram of a structure of ultrafast laser ablation micron-sized large area, which includes a micro-pore structure, a micro-groove structure and a cross structure, and the unit texture shapes are respectively circular, linear groove and square.
The ultrafast laser metal surface micro-nano texture mainly comprises two processing mechanisms of laser induction and laser etching. The laser-induced microstructure is generally in a nanometer scale, the mechanism of the laser-induced microstructure can be summarized as interference of incident laser and metal surface scattering waves, and the material is removed in a nanometer scale. Furthermore, laser etching is the processing of micron-scale structures based on the ablation of metal materials by laser beams. In a word, by the ultrafast laser micro-nano texture, the uniform tissue morphology, the uniform crystal form and the crystal grain size of the surface, the crystal grain refinement, the uniform mixed crystal state, the distortion improvement, the phase change, the phase component change and the like can be obtained, and the hardness, the corrosion resistance and the abrasion resistance of the surface modification layer are improved.
(6) And (3) carrying out corrosion resistance and abrasion resistance tests on the textured samples in all the areas, researching corrosion resistance and abrasion resistance mechanisms of the different functionalized textures, and obtaining the optimal functionalized morphology aiming at different areas on the basis of the test results to finally obtain the optimal texture characteristics and process parameters for improving the corrosion resistance and the abrasion resistance of the welding joint.
Claims (10)
1. An ultrafast laser difference micro-nano texture method for a metal welding head is characterized by comprising the following steps: (1) determining a weld joint area, a heat affected area and a base material area of the metal welding joint and differences of all areas in the phase components and the microstructure according to the measured phase components and the microstructure of the preprocessed metal welding joint; (2) according to phase compositions and microstructure of each area of a welding line area, a heat affected area and a base material area, selecting ultrafast laser cross-scale micro-nano textures in a differentiated mode, and performing ultrafast laser texturing on the surfaces and/or end faces in each area of the welding line area, the heat affected area and the base material area so as to enable the tissue appearances of the surfaces and/or the end faces in each area of the welding line area, the heat affected area and the base material area to be uniform, and/or the crystal forms and the crystal grains to be uniform, and/or the crystal grains to be refined, and/or uniform mixed crystals to be formed, and/or distortion to be improved, and/or phase and phase compositions to be changed, so that the surface and/or end face tissues in each area of the welding line area, the heat affected area and the base material area are uniform, continuous and mutually dissolved.
2. The ultrafast laser differential micro-nano texture method according to claim 1, wherein the ultrafast laser cross-scale micro-nano texture comprises a single-cycle nano-ripple texture, a double-cycle nano-ripple texture, a micro-nano grain texture or a composite micro-nano texture.
3. The ultrafast laser differential micro-nano texture method according to claim 2, wherein the composite micro-nano texture is composed of a plurality of unit textures which are arranged at intervals in a transverse, longitudinal, transverse and longitudinal vertical direction or in a transverse and longitudinal multi-angle cross arrangement with each other and have adjustable sizes.
4. The ultrafast laser differential micro-nano texture method according to claim 3, wherein the shape of the unit texture is circular, elliptical, corrugated groove, linear groove or square.
5. The ultrafast laser differential micro-nano texture method according to claim 2, wherein the shape of the composite micro-nano texture comprises a slit shape, a square lattice shape, a hole shape, a circular pit shape, an orthogonal square column shape or a parallel grating shape.
6. The ultrafast laser differential micro-nano texturing method according to claim 1, wherein the parameters of the ultrafast laser include: the pulse width is less than 12ps, the wavelength is 355-1064 nm, the power is 0-2W, and the repetition frequency is 1-100 KHz.
7. The ultrafast laser differential micro-nano texture method according to claim 1, wherein the method for measuring phase composition and microstructure of the metal welding head comprises: observing the surface appearance of the metal welding joint by using a metallographic microscope and/or a scanning electron microscope; analyzing chemical components of the metal welding head by using an EDX spectrometer carried by a scanning electron microscope; analytical testing of the phase structure and lattice parameters of metal solder joints was performed using transmission electron microscopy and/or X-ray diffractometry.
8. The ultrafast laser differential micro-nano texturing method according to claim 7, wherein the surface topography comprises grain type, and/or grain size, and/or grain distribution, and the chemical composition analysis of the metal welding head comprises grain boundaries and/or differential elemental content within the grains.
9. The ultrafast laser differential micro-nano texturing method according to claim 1, wherein the shape of the surface and/or the end surface in each of the weld zone, the heat affected zone and the base material zone is a plane or a curved surface.
10. The ultrafast laser differential micro-nano texturing method according to claim 1, wherein the pretreatment method of the metal welding head comprises polishing and cleaning in sequence, polishing to remove impurities, oxides and oil stains on the surface and end regions of the metal welding head, and then cleaning with acetone.
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