3. Technical methods for welding of aluminum alloy materials
(1) Preparation before welding
● Use chemical or mechanical methods to severely trim the outer oxide film on both sides of the weld bevel.
Chemical cleaning is the use of alkali or acid to clean the appearance of the workpiece. This method can remove oxide film and oil. The specific technical process is as follows: Immersed in 70℃ sodium hydroxide solution of 6% ~ 10% volume fraction for 0.5min → washing → neutralization treatment in nitric acid of 15% volume fraction at room temperature → washing → warm water washing → drying. The appearance of the washed aluminum alloy is matt silver white.
● For mechanical finishing, we can use pneumatic or electric milling cutters, and also use scrapers, trowels, etc. For thin oxide films, a 0.25mm copper wire brush can also be used to remove the oxide film.
Welding is done immediately after finishing treatment, if stay more than 4h, we should redo the treatment.
(2) determine the installation gap and position welding distance
During the aluminum welding process, the aluminum plate is heated and swelled, causing gaps in the bevel groove of the weld to be reduced. If the gap before installation is too small, welding will lead to the stacking of the grooves of the two plates during the aluminum welding process, and the unevenness and deformation of the plate after welding. On the contrary, if the installation gap is too large, the welding will be difficult and burn-through may occur. The proper positioning distance can ensure the required positioning gap. Therefore, selecting the appropriate installation gap and tacking distance is an effective way to reduce the deformation.
(3) Selection of welding equipment
There are many types of aluminium welding products on the market, and it is usually preferable to use TIG welding (ie, TIG welding).It is a welding method that melts the base material and the fillers welding wire by using the arc generated between the tungsten electrode and the workpiece under the maintenance of argon gas. When the aluminum welding machine is in operation, because the polarity of the connecting current is periodically changed, the half wave is a direct positive connection of current and the other half wave is a DC negative connection of current in each cycle.In the connection phase of positive half-wave, the tungsten electrode can emit enough electrons without overheating, which is beneficial to the stability of the arc.The oxide film formed on the outer surface during the negative half wave period is simply trimmed to obtain a beautiful welding seam with excellent appearance .
(4) Selection of welding wire
Usually choose 301 pure aluminum welding wire and 311 aluminum silicon welding wire.
(5) Selection of aluminum welding methods and parameters
It is usually done by a left-side aluminum welding method. The welding torch and the workpiece are at an angle of 60. When the welding thickness is 15mm or more, the right-side welding method is used, and the welding torch and the workpiece are at a 90°angle.
When workpices with more than 3mm wall thickness is welding, make the V-shaped groove, the angle is 60°~70°, the gap shall not be larger than 1mm, and shall be completed by the multi-layer welding. When the wall thickness is less than 1.5mm, the groove is not made, no gap is left, and no filler welding wire is added. When butt joint of fixing pipes is welding, if the pipe’s diameter is 200mm and its wall thickness is 6mm, a tungsten electrode with a diameter of 3 to 4mm should be selected, with a welding current of 220 to 240A, and with a filler welding wire of 4mm in diameter.Welding is completed by 2 to 3 layer.
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