Foreword
Aluminum and its alloys are increasingly used in industrial production and social life. Due to the small specific gravity, good electrical and thermal conductivity, and good castability and machinability, aluminum plays an important role in modern industrial materials.
Compared with ferrous metals, aluminum welding is more difficult, especially hard aluminum, super hard aluminum and cast aluminum. The poor welding processability of aluminum is mainly manifested in the difficulty of removing the oxide film.
In the early 1960s, the Barton Welding Institute of Ukraine invented the active flux during the welding of titanium alloys. At that time, the metal surface was coated with a thin mixture. The main role of the coating was to compress the arc instead of chemically reacting the bath. The United States Edison Welding Institute (EWI) began the development of active fluxes in the 1990s, and under the auspices of the Naval Connection Center (NJC), EWI and other members conducted process assessments. Currently, active fluxes have been commercially obtained in the United States. On the application. The TWI Welding Institute in the United Kingdom has applied active flux as the core of the research to develop more basic research.
The main role of the active flux is to compress the arc rather than chemically reacting the bath, but it is also feasible to use the active flux to crush or reduce the aluminum oxide film. The flux-cored aluminum welding wire is a brazing material and it contains some active elements. These elements can play the role of flux.
The product after the reaction of the reducing agent with Al2O3 is AlCl3 and AlxFy. AlCl3 can be converted into gas to evaporate. Al2O3 film is broken during the evaporation process of AlCl3. AlxFy is a complex salt with good fluidity, lower density than aluminum, floating on the surface and edge of the weld. The color is light gray.
The use of flux-cored aluminum welding wire for welding aluminum alloys can save energy and improve production efficiency, especially in improving the quality of welds. TIG positive electrode welding technology based on flux-cored aluminum welding wire has many advantages compared with traditional AC TIG welding. For example, the appearance of welding seam is flat, smooth, deep penetration, small slag inclusion, and almost no porosity.
1 manufacturing technology of flux cored aluminum welding wire
The manufacturing technology of the flux cored aluminum welding wire can be used for reference to the manufacturing method of the steel flux cored wire. The manufacturing process of the steel flux cored wire includes several processes such as rolling, wire drawing, post-processing and lamination. The raw material of the seamless flux-cored welding wire is a plated steel pipe. The steel pipe may be a seamless steel pipe or a welded steel pipe.
The method of producing flux-cored welding wire by using a tubular electrode method is to mix and sinter the flux core powder into a sintered flux, and then fill it into a steel tube (16-25mm) to fill the core by vibration, and then rolling, rough drawing, annealing, and thin drawing. , copper plating, layer winding and other processes to produce finished products. This method was tested in the course of the study. The reducing agent and alloy powder were loaded into an aluminum tube and rolled-draw-diffuse annealed to form a tubular electrode. The main problem is that the production efficiency is low and the filling factor of the powder is not stable.
The casting method is to add the reduced powder to the aluminum alloy ingot and compact it to form the core ingot. The brazing material is made into a porous casting blank by the previous step, and then the honeycomb billet is immersed in the active flux solution so that the solution is immersed in the voids in the billet. The ingot is cooled and then pressed. The key to the process of this method is the pretreatment and addition of active flux.
The mechanical alloying method is based on the principle of powder metallurgy, mixing, pressing and extruding powdered raw materials. The technological process is to fully mix the reducing powder, the aluminum powder and other added metal powders, pressurize the mixed metal powder at a certain temperature to form a powder ingot with a certain strength, and keep the powder in a controlled atmosphere to keep the heat and pressure. Ingots form "brazing ingots", which are extruded into finished material and reduced in diameter by drawing with a roll die.
Laminar extrusion method uses continuous casting and isothermal extrusion technology to manufacture flux-cored welding wire. Continuous casting technology can obtain uniform and stable composition of lotus root ingot. Isothermal extrusion technology can obtain flux-cored wire blank with stable filling factor. .
2 Ingot Billet Continuous Casting and Isothermal Extrusion of Flux Cored Wire
The laminar extrusion method is the extrusion of an aluminum solder ingot containing an active flux in the form of a laminar flow. The aluminum solder containing no other constituents is cast into a porous ingot in continuous casting. The outer diameter of the ingot is The inner pore size is constant and the active flux is filled into the inner pores and compacted.
The compacted solder paste containing active flux has the following characteristics: the ratio of flux to solder is constant at different cross sections; reinforcing particles (such as SiC) can be added to the active flux to form a composite material; the flux is fully coated with solder .
The key technology of the laminar extrusion process is the sequential flow of flux and solder. The condition of sequential flow is the consistency of the rheological properties of the two materials. The rheological properties of the material are related to the temperature and compressive stress, and the extrusion temperature and extrusion are adjusted. The pressure can make the rheological properties of two different materials similar, and a well-designed extrusion die shape can make both materials stably deform in laminar flow.
The isothermal extrusion technology was used in the research process. A flux-cored wire with stable cross-section and uniform fill factor can be obtained under specific extrusion temperature and extrusion speed conditions.
3 Flux cored wire drawing and layer winding
Compared with the solid wire, the main features of the internal structure of the flux cored aluminum wire are as follows: The core is loose sand-like, non-viscosity, and non-plastic. The deformation and flow of the core are mainly due to the extrusion force generated when the surrounding material is deformed and Friction; welding wire deformation capacity significantly reduced.
In the drawing process of the flux-cored wire, the deformation of the wire is divided into two parts, one is the plastic deformation of the metal, and the other is the flow and volume compression of the internal powder. These two types of deformation interact and influence each other. The metal plastic deformation ability determines whether the drawing can be performed continuously. The rheological behavior of the drug core and the degree of volume compression are related to whether the fill factor of the flux cored wire is stable or not, thereby affecting the use of the flux cored wire and the stability of the welding process.
Due to the presence of the drug core, the effective cross-sectional area of ​​the flux-cored wire is much smaller than that of the solid wire, so the phenomenon of broken wire during the drawing process of the flux-cored wire is widespread. It is an effective way to improve the drawing processability of the cored aluminum wire by optimizing the wire deformation method during the drawing process. The roll mold drawing technology used in the study improves the wire deformation mode and significantly improves the wire deformation capability.
The flux-cored wire drawn to the finished size is wound into a disk using a lamination technique.
4 Conclusion
(1) There are four methods for manufacturing the flux cored aluminum welding wire studied, of which the laminar extrusion method has more industrial application prospects.
(2) Continuous casting technology can obtain a uniform lotus root ingot with stable composition, and isothermal extrusion technology can obtain a flux core blank with a stable filling factor.
(3) The roller die drawing guarantees the uniform deformation of the core, and the ultra-scratching technology ensures the cleanliness of the welding wire. The layering technology ensures the stability of the welding wire during welding.