With the current development of lightweight, many body or chassis parts have begun to use aluminum parts on a large scale to reduce vehicle weight. Especially in current electric vehicles, because the battery pack and motor are too heavy, designers have to reduce the weight from other places to control the weight of the vehicle.
A Common Aluminum Beam
The general structure of this one-piece aluminum beam is made of aluminum alloy, which is welded by vacuum electron beam welding and MIG welding, and other iron parts are assembled on the aluminum alloy with standard parts. (The thickness of aluminum alloy in the picture is 3.0 mm)
The welding service of aluminum alloy is different from the welding of general carbon steel, stainless steel, etc., and there are many problems to be solved.
The following describes how to weld aluminum alloys from the characteristics of aluminum alloy materials in welding, welding difficulties, and solutions.
Characteristics and welding difficulties of aluminum alloy materials in the welding process
- The thermal conductivity is very large, about 2 to 4 times that of steel, and the heat resistance is very poor. Generally, aluminum alloys are not resistant to high temperature, and the expansion coefficient is large, which is prone to welding deformation, and the tendency of welding cracks is also obvious. The thinner the aluminum alloy sheet, the more difficult it is to weld, and the easier it is to weld through.
- It is very easy to generate pores in the welding of aluminum alloys. Since the hydrogen in the molten pool cannot be discharged before the welding seam is formed, there are pores in the welding seam.
- When the surface of aluminum alloy is directly exposed to the air, it is very easy to produce a layer of refractory oxide mold (the composition is aluminum oxide) on the surface. The melting point of this oxide mold is as high as 2050 degrees. There will be cases where the oxide mold cannot be penetrated and cannot be welded.
- The welding joint of aluminum alloy is seriously softened, and the strength coefficient of the weld is lower than that of the base metal.
- The surface tension of the aluminum alloy material is small in the molten state, and it is easy to dent.
According to the characteristics and welding difficulties of aluminum alloy materials, welding requirements
The Requirements For Welding Equipment
First, let’s talk about the welding equipment when using the MIG/MAG welding method. MIG/MAG welders that are required to weld aluminum alloys must have a pulse function, including single and double pulses. It is best to weld aluminum alloys with double pulses. In short, double pulses are superposition of two pulses, and a fixed high-frequency pulse is superimposed with a low-frequency pulse, which is high-frequency pulse low-frequency modulation. Adding a low-frequency pulse to a high-frequency pulse makes the double-pulse current switch between the peak current and the base current at a certain frequency (the frequency of the low-frequency pulse), so that the weld can form a regular fish scale pattern.
In the welding process, by adjusting the frequency of the low-frequency pulse, the peak value of the low-frequency pulse, and the base current to improve the weld formation, first of all, adjusting the frequency of the low-frequency pulse determines the switching speed between the double-pulse peak current and the base current, which is reflected in the welding effect. It is the degree of close fit of the fish scale pattern of the weld.
The low frequency pulse frequency is low, the switching speed between the double pulse peak current and the base value current is slow, and the distance between the fish scale lines is large; on the contrary, the frequency of the low frequency pulse is high, and the double pulse peak current and base value current. The switching speed is fast, and the distance between the fish scale patterns of the weld is small and fine. The corresponding penetration depth can be obtained by adjusting the peak current and base current according to the thickness of the plate.During the mutual switching process of the peak current and the base current, the molten pool can be effectively stirred, and the hydrogen gas can be discharged to reduce pores; reduce the heat input to the base metal and prevent The overheating of the aluminum alloy material causes expansion and deformation, and it can also make the weld structure finer, so that the strength of the weld is improved.
The Precautions For Welding Aluminum Alloys
- Before welding the aluminum alloy, the surface of the aluminum alloy should be cleaned first. There should be no oil stains, dust, etc. The surface of the aluminum alloy welding can be cleaned with acetone. The thick aluminum alloy should be cleaned with a wire brush, and then cleaned with acetone.
- The selection of welding wire should be as close to the base metal as possible, and the selection of aluminum-silicon or aluminum-magnesium welding wire should be determined according to the requirements of the weld.In addition, the aluminum-magnesium welding wire can only weld aluminum-magnesium materials, while the aluminum-silicon welding wire can weld both aluminum-silicon and aluminum-magnesium materials.
- When the plate is thick, it is necessary to preheat the plate to prevent the welding from being impervious due to insufficient preheating. When the arc is closed, the arc should be filled with a small current.
- It is best to use double pulse
- AC and DC argon arc welding machine should be used for tungsten electrode argon arc welding, and the welding current is switched between positive and negative. When the tungsten electrode is at the positive electrode, it is used to clean the oxidation mold on the surface of the aluminum material, and when the tungsten electrode is at the negative electrode, the welding is performed.
- The welding specification should be set according to the thickness of the plate and the requirements of the weld
- MIG welding should use a special aluminum wire feeder, and use a Teflon wire guide tube, which does not produce aluminum scraps
- The length of the welding torch cable should not be too long, the aluminum welding wire is soft, and the long welding torch cable will affect the wire feeding stability.
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