Welding aluminum alloy is very different from welding general carbon steel, stainless steel and other materials.
It is easy to produce many defects that other materials do not have, which need to be avoided through specific measures.
Let's take a look at the problems that can occur when welding aluminum alloys and the requirements of the welding process.
Difficulties of welding aluminum alloy materials
The thermal conductivity of aluminum alloy is 1 to 3 times that of steel and is easy to heat.
However, this material is not resistant to high temperatures and has a large expansion coefficient due to temperature rise, which is easy to cause deformation when welding.
In addition, this material is easy to crack and weld during welding, especially the welding of thin aluminum plates is more difficult.
Aluminum alloy welding will produce a certain amount of hydrogen in the molten pool.
If these gases are not discharged before weld formation, they will cause pores in the weld and affect the quality of welds.
Aluminum is an easily oxidized metal. There is almost no unoxidized aluminum in the air.
When the surface of aluminum alloy is directly exposed to air, a dense and insoluble layer of aluminum oxide film will form on the surface.
The oxide film and its wear resistance and high temperature resistance have a melting point of more than 2000 ℃.
Once formed, the difficulty of subsequent processing will greatly increase.
There are also some problems in welding aluminum alloys, such as easy softening of joints, low surface tension in the molten state, easy production of defects and so on.
Requirements for aluminum alloy welding process
First of all, from the perspective of welding equipment, if a MIG/MAG welding machine is used, it must have pulse function, such as single pulse or double pulse.
The best is the double pulse function.
Double pulse is the superposition of high frequency pulse and low frequency pulse. The low frequency pulse is used to modulate the high frequency pulse.
In this way, the double pulse current is fixed and periodically alternates between the peak current and the base current at the frequency of the low-frequency pulse, so that the weld can form regular lines of fish scales.
If you want to change the weld forming effect, you can adjust the frequency and peak value of the low frequency pulse.
Adjusting the low-frequency pulse frequency will affect the switching speed between the peak value and the base value of the double pulse current, which will change the spacing of the fish scale lines in the weld.
The higher the switching speed, the smaller the spacing of the fish scale pattern.
Adjusting the peak value of the low frequency pulse can change the stirring effect in the weld pool, so as to change the welding depth.
Choosing the appropriate peak value has obvious effects on reducing pore generation, reducing heat input, preventing expansion deformation and improving weld strength.
In addition, from the perspective of the welding process, attention should be paid to the following matters:
First, clean the aluminum alloy surface before welding, and all dust and oil stains should be removed.
Acetone can be used to clean the surface of the aluminum alloy welding joint. For thick aluminum alloy plates, first clean them with a wire brush and then clean them with acetone.
Secondly, the material of the welding wire used should be as close as possible to the base metal. The choice of aluminum-silicon welding wire or aluminum-magnesium welding wire should be determined according to the welding requirements.
In addition, aluminum and magnesium welding wire can only be used to weld aluminum and magnesium materials, while aluminum and silicon welding wire can be used to weld aluminum, silicon and aluminum and magnesium materials.
Third, when the thickness of the plate is large, the plate must be preheated in advance , otherwise it is prone to incomplete welding and the well must be filled with small current during arc closure.
Fourth, when tungsten argon arc welding is carried out, a DC argon arc welding machine must be used, and AC and DC forward and reverse must be used alternately.
Direct DC is used to clean the oxidation mold on the aluminum surface, and reverse DC is used for welding.
In addition, it should be noted that welding specifications are set according to the plate thickness and welding requirements;
Special aluminum wire feed wheel and Teflon wire guide tube must be used for MIG welding, otherwise aluminum chips will be generated;
The length of the welding gun handle should not be too long.
Aluminum welding wire is soft. Too long welding gun handle will affect wire feeding stability.
