Preparation of aluminum alloy before welding
18 \ Feb
Treatment of bevel
The butt weld under 3 mm thickness can not open the groove, only a 0.5 to 1 mm angle on the back of the weld is needed, which is beneficial to the discharge of the gas and the avoidance of the back groove. The influence of backside is on the weld line. The groove angle of aluminum alloy thick plate is larger than that of steel plate. The single side groove generally adopts 55 degree groove, and the double side groove adopts 35 degree groove on each side. This can increase the accessibility of welding and reduce the probability of failure of non fusion defects.
Welding aluminum alloy needs the cleanest preparation, otherwise its corrosion resistance will decrease, and it will easily produce pores. The welding aluminum alloy should be completely distinguished from the custom of welding steel. It is used for welding steel used tools and strictly prohibit welding aluminum alloy. Clean the oxide film and other impurities in the weld area, and use stainless steel brush or acetone as much as possible. Cannot use the grinding wheel, because of the use of grinding wheel will only make oxide film in fusion welding surface, but does not really remove. And if the hard grinding wheel is used, the impurity will enter the weld and cause the hot crack. In addition, the Al2O3 film will be regenerated and accumulated in a short time. In order to make the oxide film as little as possible to affect the weld, it should be immediately welded after cleaning.
In the welding of thick plates with plate thickness exceeding 8 mm, preheating should be carried out before welding. The preheating temperature is controlled between 80 and 120, and the interlayer temperature is controlled between 60 and 100. In addition to the high preheating temperature, in addition to the bad working environment, it may have an effect on the alloy properties of the aluminum alloy, the joint softening, the appearance of the weld appearance and so on. The interlayer temperature is too high will make the aluminum welding hot crack probability increase.
The physical and chemical properties of aluminum alloy and steel are far from each other. We must test and determine the welding specification parameters based on the welding characteristics of aluminum alloy.
5.1 welding current is larger
The thermal conductivity of aluminum alloy is about 4 times larger than that of steel, and the heat dissipation is fast. Therefore, at the same welding speed, the heat input of welding aluminum alloy is 2~4 times larger than that of welding steel. If the heat input is not enough, it is easy to appear the problem of insufficient penetration or even no fusion, especially in the beginning of weld seam.
5.2 wire feeding speed should be properly adjusted
Wire feeding speed is closely related to the specification parameters such as current and voltage, and matches each other. When the welding current is increased, the wire feeding speed should also be increased correspondingly.
5.3 selection of welding speed
For thin plate welds, in order to avoid overheating of the weld, the smaller welding current and faster welding speed are generally adopted. For the thick plate weld, the welding current and the slower welding speed are adopted to make the weld fusion full and the weld gas fully escape.
Selection of the angle of 5.4 welding gun
In the welding direction, the angle of the welding torch is generally controlled at about 90 degrees. Too large and too small will cause welding defects. The welding gun angle causes the gas protection to be insufficient and the gas hole is produced, and the small angle can also make the liquid aluminum reach the front of the arc, so that the arc can not be directly acted on the weld to produce the non fusion.