The main points of welding of aluminum and aluminum alloy electrode arc welding are as follows:
1 . Selection and use of welding rod
   Pure aluminum electrode is mainly used for welding aluminum and aluminum alloy with low joint performance. The weld of aluminum-silicon welding rod has good crack resistance, aluminum-manganese electrode has good corrosion resistance, and aluminum-magnesium electrode has higher Strength of. The aluminum electrode strips are all salty and are susceptible to moisture, so they should be stored in a dry place. The performance and use of common aluminum and aluminum alloy electrodes are shown in Table 10-31 .
   Table 10-31 Performance and Use of Common Aluminum and Aluminum Alloy Welding Rods
   Before use, the electrode should be baked at 1500C for 1 ~ 2h . Store it in a dry and sealed electrode barrel to avoid moisture. It is welded by DC power supply and the welding rod is connected to the positive pole.
2 . Opening of the groove
   The thickness of the plate is less than 6mm , the groove is not opened, the plate thickness is 6~12mm , the V -shaped groove is opened, and when the plate thickness is more than 12mm , the X -shaped groove with the angle of 70 ° is opened.
3 . Pre-weld cleaning
   Pre-weld cleaning is an important process to ensure the quality of aluminum and aluminum alloy welding. Before the welding, the oxide film and oil stain at the weld of the workpiece should be strictly removed, otherwise the weld will be poorly fused. The quality of the cleaning will directly affect the stomatal tendency and mechanical properties of the weld.
4 . Pad
   Aluminum has a low strength at high temperatures, and metals tend to collapse when welded. In order to ensure the penetration and not collapse, the pad is often used to support the molten metal. The pad can be made of graphite plate, stainless steel plate or carbon steel plate, and a circular arc groove is formed on the surface of the pad to ensure the formation of the reverse side of the weld. Generally, when welding on site, it is required to have no padding, and single-sided welding is formed on both sides, but it requires skilled operation.
5 . Preheating before welding
   Thin aluminum parts generally do not require preheating. For aluminum parts with a thickness of more than 5mm , in order to achieve the required welding temperature near the weld to prevent deformation and reduce defects such as pores, preheating should be carried out before welding. Generally, the workpiece is slowly heated to 100~300 °C, and oxyacetylene flame can be used. Heated by electric stove or torch.
6 . Operation essentials
   When the arc is started at the arc or joint, the arc should be longer, so that the tip of the electrode is sprayed with droplets. After the molten pool is filled with liquid metal, the arc length should be gradually shortened. When the arc is extinguished, fill the crater and slowly remove the arc. The melting speed of the aluminum electrode is about three times larger than that of the steel electrode, so rapid welding is required. During the welding process, the electrode should be reciprocating linearly perpendicular to the surface of the weldment. The arc should be as short as possible to prevent metal oxidation, reduce spatter and increase penetration depth. Replacing the electrode must be done quickly. Preheating measures are required for thick weldments.
   The welding repair of aluminum-magnesium castings should use thinner welding rods and smaller welding currents to prevent collapse when the current is too large, but the welding current of aluminum castings should be slightly larger than the welding plates. When welding multiple cracks in aluminum castings, the small cracks should be repaired first, and then the large cracks should be repaired. The long cracks are segmentally welded, that is, each length is 60~70mm , first welded from the middle of the crack to the other end, and then returned to the middle of the crack to the other end.
   Multi-layer welding or welding repair should be layer by layer to avoid slag inclusion. After the welding is finished, the weld slag on the weldment surface should be carefully removed to prevent corrosion of the weldment.
   After the casting is repaired, the whole annealing should be carried out, the annealing temperature is 300~350 °C, and slow cooling is carried out to improve the weld metal structure and eliminate the residual stress of the welding.
   Table 10-32 shows typical welding specifications for arc welding of aluminum and aluminum alloy electrodes.
   Table 10-32 Typical welding specifications for arc welding of aluminum and aluminum alloy electrodes
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