Aluminum and its alloys in industrial production and social life has been used widely, because the proportion of small, good electrical and thermal conductivity, casting and machining of quality aluminum materials in modern industry's important role is irreplaceable.
Compared with black metal, aluminum welding more difficult, especially in hard aluminum, super-hard aluminum and cast aluminum. Poor welding of aluminum is mainly manifested in the oxide film is difficult to remove.
Barton Welding Institute of Ukraine in the early 1960s when the invention of the active titanium welding flux, was coated with a thin layer on the metal mixture, coating the main role is to compress the arc, rather than the chemical reaction of the bath. U.S. Edison Welding Institute (EWI) in the 1990s the development of active flux, and the Navy connection center (NJC), with funding from the EWI and some other members of the assessment process, the current flux in the United States has a commercial activity on the application. TWI Welding Cable Institute UK has applied to start the core activity of flux as basic research studies.
The main role of reactive flux compression arc, rather than the chemical reaction of the pool, but also the use of flux activity broken or aluminum oxide film is feasible. Aluminum-cored solder wire is, itself contains some active elements, these elements can play a role in flux.
Reducing agent and the reaction product of Al2O3 is AlCl3 and AlxFy, AlCl3 can evaporate into a gas, AlCl3 evaporation process also broken Al2O3 thin films; AlxFy is a compound salt, good fluidity, density less than aluminum, floating on the weld surface and edge of the light gray color.
Use of aluminum-cored wire welding aluminum can save energy, improve production efficiency, particularly in enhancing the quality of the weld with remarkable success. Based on aluminum-cored Welding Wire for TIG welding process is polar, with the traditional AC TIG welding compared to many advantages, such as weld appearance, smooth, melt deeply, less slag, almost no holes and so on.
1 cored aluminum wire manufacturing technology
Aluminum-cored wire manufacturing technology can learn from the steel flux cored wire manufacturing method, the steel flux cored wire manufacturing process consists of rolling, drawing, and post-processing layer around several processes. Seamless flux cored wire for the raw materials into a plate of steel, seamless steel pipe can also be a welded steel pipe.
Tubular cored electrode manufacturing method is to first mix cored powder sintering sintering flux form, then fill in the pipe (16-25mm) through the vibration of the cored fill real, then by rolling, rough drawing, annealing, small pull , copper, and other processes in the system layer around the finished product. Course of the study have tried this method, the reducing agent into the aluminum in the alloy powder, rolling - drawing - diffusion annealing, the final formation of tubular electrode. The main problem is low productivity, powder filling factor of instability.
Casting is to restore the powder into aluminum ingots, fully formed cored tablet compaction. The first step to solder made of porous cast blank, and then immersed in the honeycomb blank activity flux solution, immersed in the solution in the blank spaces. Ingot to cool before squeezing. The process of this method lies in the pre-activated flux and add process.
Mechanical alloying powder metallurgy method is based on the principle of mixing the powdered raw materials, pressing, extrusion. The process is to restore the powder, aluminum powder, metal powder, well mixed add the other, to a certain temperature mixed metal powder under pressure, to form a certain strength of powder tablets, in a controlled atmosphere, heat, and pressure to powder ingot form a "brazing ingots," and finally become useful and extrusion die drawing method with reduced roll diameter.
Laminar flow is the use of continuous casting extrusion and isothermal extrusion technology to produce flux cored wire, continuous casting technology can be homogeneous, composition and stability of the "Lotus" ingot, isothermal extrusion technology can fill factor to obtain a stable rough flux-cored wire .
2 of ingot casting and flux-cored isothermal extrusion
Laminar flow is extrusion of aluminum containing active solder flux ingot to form laminar flow extrusion, aluminum-free solder other group element cast in the form of porous ingot casting, ingot diameter and the hole size constant, the activity of flux within the hole to fill and compacted.
After compaction of the tablet containing the active solder flux has the following characteristics: at different cross-section, the proportion of constant flux and solder; activity can be added to enhance the flux of particles (eg SiC) to form a composite material; full package solder flux is deposited .
Laminar flow extrusion process technology is the key order of solder flux and flow, the formation conditions of the order flow is consistent rheological properties of two materials, the rheological properties of the stress associated with temperature and pressure, adjust the extrusion temperature and extrusion Stress can make two different rheological properties of materials similar to well-designed extrusion die shape can always make the two materials form stable laminar flow deformation.
(1) The welding current in order to improve the rate of melting is necessary to increase the welding current, welding current increases, the melting rate of the welding material will significantly improve. But for a certain diameter of the wire in terms of its current capacity there is a certain limit. When the welding current increases to a certain extent, the welding arc shape and droplet transfer forms will change significantly. When using the filaments, the welding current increases to a certain extent, will be unstable rotating jet transition, this time droplet often is the horizontal throw to become splash, welding process is very unstable. Thick filament current welding, such as SAW, with the increase of the welding current, wire melting rate increased, but at the same heat input of the workpiece increase as welding heat input to improve for high strength steel and special-use materials welding is very inappropriate. In this case, in order to ensure welding quality improve welding productivity, process measures must be assisted to improve the welding current.
(2) wire stem elongation under the same welding current, the stem elongation increases wire can also increase the melting rate of the wire. C2 in Figure 1 represents the ohmic heat generated in the wire current is proportional to the square of this wire melting rate is very important. Wire resistivity will wire temperature increase with the increase of welding current, the wire resistivity will increase. Figure 2 apply for three different dry stretch the length of the wire melting curve of the relationship between efficiency and current. It can be seen from Figure 2 in the same welding current circumstances, with the increase of stem elongation, wire deposition efficiency improved significantly. Therefore, in the high-current welding, the ohmic heat generated in the wire on the wire melting rate plays a vital role.
(3) the polarity of the deposition efficiency of different polarity Welding Wire and base metal deposition efficiency is different. Under normal circumstances, MIG welding using DCEP (DCRP), DCEP can achieve a greater penetration depth and can prevent the penetration depth less than the defect. Figure 3 and Figure 4 shows the relationship between the polar and penetration as well as wire deposition efficiency. It can be seen that the DCRP can get a larger penetration depth, but the smaller the wire deposition efficiency; DCEN is (DCSP) wire can obtain a higher deposition efficiency, but the base metal penetration small.It can be seen from Figure 3 and Figure 4, can be adjusted by changing the polarity of the deposition efficiency of the melting rate of the base metal and wire, to meet the requirements of the different welding processes. If the requirement to increase the penetration of the base metal, you can use DCEP; welding sheet can be used DCEN is to reduce the penetration of the base metal, and increased the melting efficiency of the wire, and ultimately high-speed and efficient welding.
(4) wire diameter Figure 5 illustrates the different diameter of wire deposition efficiency under different welding parameters. It can be seen, in the same welding current circumstances, as the wire diameter decreases, the welding current density increased, wire deposition efficiency increased; the contrary, to maintain the efficiency of the deposited certain, with the reduction of wire diameter small welding current decreases, the corresponding heat input to the workpiece is also reduced, that is the same under the premise of the deposition efficiency can reduce the heat input to the parent metal, the Welding Flux of high strength steel and special purpose steel is very beneficial the. Therefore, the welding workers in efficient MIG / MAG welding process, most of the filaments, large current welding is the use of the above advantages. 1.2mm wire, such as TIME welding process and the maximum wire feed speed up to 50m/min. LINFAST and double-wire TANDEM welding processes are used filaments of 1.2mm. Filaments welding An additional advantage is the stability of the arc in the welding of the small current increase, the impact of the weld pool decreases, thereby maintaining uniform penetration.
(5) the impact of shielding gas for MIG / MAG shielding gas research has been carried out for many years, the role of the protective gas in the welding process is mainly manifested in the following aspects: (1) to improve the arc stability. â‘¡ improving droplet transfer. â‘¢ improve the mechanical properties of the weld metal. (4) improve the welding productivity. â‘¤ to reduce the possibility of welding defects, such as porosity, lack of fusion. In addition, due to the different gases of different physical and chemical properties, the role played by it in the welding process is not the same, the choice of shielding gas for different process conditions, different applications and different.