Welding light metals such as aluminium represent a challenge compared to what can be welding steel alloys. And it is that welding aluminium requires excellent precision in order to achieve a solid bond. But what kind of welding will allow us this? If you do not know very well the types of welding that exist, the difference between each of them and the advantages and disadvantages, visit our article dedicated to the different types of welding.
But do not worry, because in this article we will explain everything you need to know to learn to weld aluminium. In addition, we show the different methods that can be used for welding aluminium, and the choice will depend on the particular needs of your project. Let us begin!
- 1 Before We Start
- 2 Weld Aluminium with TIG
- 3 Weld Aluminium by an electric arc with coated electrode
- 4 People also ask
Before We Start
It is best to go step by step, so first, we will explain what you should know before you start welding. Thus, you can understand the whole process better and make a better choice of your method.
What is aluminium?
Aluminium is a light and thin metal and is one of the most used materials in the world of welding. Despite being light (the density of aluminium is one-third of that of steel), is strong and resistant, and that makes it so popular.
It has a very low melting point, of about 660 ° C, and is a very conducive element, both electricity and heat. This is why pure aluminium is widely used in electrical applications since its electrical conductivity is superior to all alloys.
It is a very ductile metal and has a very low mechanical resistance. Therefore, it is usually alloyed with different metals to harden and improve mechanical characteristics. And in this way, the alloys have better mechanical strength than pure aluminium.
Why is aluminium so difficult to weld?
The aluminium must be welded at a low temperature, and having a lower melting point and a very high conductivity, if this is not done, burns will be created and it will end up boring the metal.
In addition, it is a fairly reactive material, and that causes it to form an oxide layer when exposed. The result of this quality is usually porous welds, which is a problem. To avoid this, you have to clean the aluminium well before welding (we will explain later), and work very quickly, since in a few minutes it usually comes out again.
As we have mentioned, aluminium is alloyed with different metals to achieve stronger and more durable metals. Normally, these alloys are created with copper (Cu), Magnesium (Mg), Silicon (Si), and Zinc (Zn). To this, other metals are added in small quantities, such as Chrome (Cr), Iron (Fe), Nickel (Ni) and Titanium (Ti). Thus, there are a lot of aluminium alloys, all of them with characteristics superior to pure aluminium.
These alloys can be obtained by different techniques, as well as by moulding or by processes that lead to deformation, such as lamination and forging.
Classification of aluminium alloys
There are many types of aluminium alloys, as just mentioned, but in this section, we will only take into account the aluminium alloys for forging, since these are the ones that are used for welding.
Regarding the classification, we can distinguish two different classifications, the first is the nomenclature and classification according to UNE 38-300, and the second is the nomenclature according to the Aluminium Association (AA), also known as the American classification.
According to UNE 38-300, aluminium and aluminium alloys for forging constitute the L-3XXX series. This series is classified into different groups, according to the main alloy elements. And according to the Aluminium Association classification, each alloy is given a four-digit number, and the first is the one that shows the main alloys.
|Alloy||UNE 38-300||Aluminium Association|
|Aluminium (minimum purity: 99.00%)||Group L-30XX||1XXX|
|Aluminium-Copper Alloys (Al-Cu)||Group L-31XX||2XXX|
|Aluminium-Magnesium Alloys (Al-Mg)||Group L-33XX||5XXX|
|Aluminium-Magnesium-Silicon Alloys (Al-Mg-Si)||Group L-34XX||6XXX|
|Aluminium-Silicon Alloys (Al-Si)||Group L-35XX||4XXX|
|Various alloys||Group L-36XX||8XXX|
|Aluminium-Zinc Alloys (Al-Zn)||Group L-37XX||7XXX|
|Aluminium-Manganese Alloys (Al-Mn)||Group L-38XX||3XXX|
|Aluminium-Tin Alloys (Al-Sn)||Group L-39XX||–|
Characteristics and weldability of alloys
Once we have seen what are the forging alloys, we will see what are the characteristics of each of them, and the weldability of each of them. Among all these alloys, we can also distinguish two different groups in terms of weldability.
And we can distinguish between bondable alloys (heat-treatable alloys), and non-bondable, these being non-heat treatable alloys. The heat treatment known as the bonus consists in heating the material to 500 ° C, to cool it very quickly, and according to the alloy, maturation will be carried out, which can be both natural and artificial. The first is to keep it at room temperature, while the second is about 200 ° C.
When this treatment is performed on the bondable alloys, its hardness and mechanical strength increase. But non-bonuses do not change their properties with treatment.
Next, we will show which alloys are non-bondable, since alloys of this type are weldable. As for bonus alloys, welding is not recommended for many of the alloys, although there are some that can be welded. Let’s go there!
This is the L-30XX Group according to the UNE, and 1XXX according to AA. These alloys, having a minimum purity of% 99, are almost pure Aluminium. And as we have said before, pure Aluminium is mainly used in electrical applications.
These types of alloys are non-bondable, being weldable for it. The most important weldable alloy of this group by the TIG and MIG processes is the L-3001 (UNE) / 1100 (AA) alloy. Although this alloy is also weldable by other types of welding, such as point resistance or seam, with strong welding or soft welding.
Aluminium and Copper Alloys
This is the L-31XX Group of the UNE nomenclature, and 2XXX of the AA. Normally, these alloys are made of copper and coated with Aluminium. They are very strong materials, but not very resistant to corrosion. It is usually used mainly in the manufacture of aeroplanes.
These are bonus alloys, so for most of the welding is not recommended. However, the L-3191/2219 alloy can be welded by TIG and MIG and by resistance by stitches or by seam, and the alloy L-3140/2024 by resistance by stitches or by the seam.
Aluminium and Magnesium Alloys
These alloys are within the L-33XX Group of the UNE, and 5XXX within the AA nomenclature. These are easy to use metals, and they are also resistant to corrosion. But, instead, they are not the strongest metals mechanically. In addition, special care must be taken, and temperatures too low should be avoided, as it can be dangerous.
There are some bonus and some non-bonus alloys, and there are many alloys that can be welded, either by MIG / TIG or by resistance by stitches or by sewing. These weldable alloys are the following: L-3360 (UNE) / 5052 (AA), – / 5652, L-3321/5083, L-3322/5086, L-3390/5454
and – / 5456.
Aluminium, Magnesium and Silicon Alloys
Aluminium, magnesium and silicon alloys are part of the UNE Group L-34XX and 6XXX in regard to the Aluminium Association. They are quite strong and versatile alloys and stand out because they can be treated with heat. This is because of the proportion they contain silicon and magnesium.
These alloys are bondable, but still and most, most of the alloys can be welded by MIG / TIG, by point resistance or by a seam or by strong welding. Some of them, also by gentle welding. Here are the weldable alloys: L-3420/6061, L-3441/6063, and finally, L-3431/6101 and L-3451/6351, which can also be welded by soft welding.
Aluminium and Silicon Alloys
These Aluminium and silicon alloys are named as Group L-35XX, and as 4XXX in the AA. The silicon contains causes the melting point of Aluminium to be greatly reduced. Therefore, it is not uncommon to find welding electrodes of this group.
However, there are bonus alloys and non-bonus alloys, and welding by typical processes is not recommended for alloys of this type.
In Group L-36XX belonging to the UNE, what would be the nomenclature 8XXX of the AA? Since they are different alloys, you cannot have an exact description of them.
Aluminium and Zinc Alloys
The Aluminium and Zinc alloys constitute the L-37XX Group, and the 7XXX of the UNE and AA respectively. These alloys have very high resistance, so they are also widely used in aeronautics. In addition to Zinc, they usually contain some magnesium, which means they can be heat treated.
They are bonus alloys, and although the vast majority cannot be welded, there are some alloys suitable for welding by MIG / TIG processes and spot welding or sewing, such as L-3741/7005, L-3731/7039. And the L-3710/7075 alloy can be spot welded or sewn.
Aluminium and Manganese Alloys
The L-38XX Group of the UNE and the 3XXX of the AA name the Aluminium and Manganese alloys. They usually have about 1.5% manganese. The biggest advantage is that they are very easy to work, and although they cannot be treated with heat, this alloy is a good option to enter the world of Aluminium welding and Aluminium alloy welding.
Aluminium and manganese alloys are non-bondable, and two alloys stand out for their weldability; L-3810/3003 and L-3820/3004. The first can be welded with TIG / MIG and by resistance by a point or by seam, and the second, in addition to these processes, can also be welded by strong welding and soft welding.
Aluminium and Tin Alloys
These alloys do not have a nomenclature in the AA but are from the L-39XX Group of the UNE.
Recommendations to start welding
Now that you know a little more about aluminium and its characteristics and weldability, we are going to tell you the steps you must follow to finally be able to start welding.
Clean from aluminium
To be able to weld without problems, the Aluminium parts have to be extremely clean. This is because Aluminium usually forms a thin layer of aluminium oxide, which melts at a much higher temperature than Aluminium. This is a danger since if there is a little bit of rust, it can generate inclusions of rust in the weld, reducing the resistance of the weld.
The simplest way to perform this cleaning is usually mechanical, doing it with a wire brush. Always be sure to use clean brushes or brushes that have only been used to clean Aluminium. And is that the brushes used with other metals can leave some traces of those metals that can then affect the quality of the weld. Another thing to keep in mind is to brush gently because if you do it sharply you can embed the oxides more in base Aluminium.
Select the appropriate input material for Aluminium
Both rods and coated wires and electrodes can be used as filler metal for Aluminium welding:
Coated electrodes for welding Aluminium
Coated electrodes are used with direct reverse polarity (DC +) current. You must be very careful with moisture, and better if you dry them before using them for welding, otherwise, they can produce spores. You must choose the most similar to your base Aluminium, these being the most common electrodes:
|Electrode designation||Electrode composition|
|E 1100||Pure Aluminium|
|E 3003||Aluminium – 1% Manganese|
|E 4043||Aluminium – 5.2% Silicon (Alloy for the manufacture of electrodes and welding rods)|
Wires and rods for welding Aluminium
In the same way, if you are going to choose a rod, select an Aluminium filling material of a melting temperature similar to that of the base Aluminium. Keep in mind that the rods have to be clean to get a good weld. The most common is usually the 4043 and 5356 alloy rods, if you don’t have it very clear, you can opt for either.
|Rod Designation||Chemical composition of the rod|
|ER 1100||Pure Aluminium|
|ER 2319|| Aluminium – 6% Copper – 0.3% Manganese (It is a variant
|ER 4043|| Aluminium – 5.2% Silicon (Alloy intended for
electrode and rod manufacturing)
|ER 4047||Aluminium – 12% Silicon|
|ER 4145||Aluminium – 10% Silicon – 4% Copper|
|ER 5183|| Aluminium – 4.5% Magnesium – 0.65% Manganese (It is a
|ER 5356||Aluminium – 5% Magnesium – 0.3% (Manganese + Chrome)|
|ER 5554||Aluminium – 2.9% Magnesium – 0.65% Manganese|
|ER 5556||Aluminium – 5% Magnesium – 0.7% Manganese|
|ER 5654||Aluminium – 3.5% Magnesium|
Use a fill rod of the same size as the tungsten electrode.
Hold the workpieces
Before you start welding, you have to make sure that the pieces you have to weld are not going to move during the whole process. To do this, you can use clamps, and thus securely attach them to your worktable.
Never forget about protection
As we mentioned in all our articles, protection is vital for welding, so the more you protect yourself, the safer you will work. You don’t need to have the complete equipment, but at least you should have the gloves and the darkening helmet.
Also recommended are the welding apron, the respiratory mask and safety shoes.
Preheat the Aluminium
Preheating, in general, is usually not necessary. But the pieces of great thickness are an exception since in this case, the preheating can reduce the thermal contribution to obtain the suitable fusion.
Preheating is usually usual when using the TIG process, but not when using the type of MIG welding.
Weld Aluminium with TIG
TIG welding is the most commonly used process for welding Aluminium. And it is that a welding machine that can control the current is very useful to prevent the Aluminium part from overheating and causing burns. This is because Aluminium needs a lot of heat to reach its temperature, but once it reaches it can keep a long time. In addition, TIG welding can be used in both thin Aluminium and thicker Aluminium.
Before starting with all the steps, I leave you a great video about TIG welding for Aluminium:
For TIG welding of Aluminium, a shielding gas is used. Argon is normally used, due to its good cleaning action and penetration profile, and 3% helium can also be added for greater arc stability. But if what is going to be welded is an Aluminium and magnesium alloy, a mixture of argon with helium (a maximum of 75% helium) is recommended to minimize the creation of magnesium oxide.
TIG welding for Aluminium with the direct-current negative electrode (CC-)
Steps to follow to weld Aluminium with TIG
- Set the correct amperage for your project. You have to calculate that you need 1 amp for every 0.025 mm thick Aluminium. Do the approximate calculation, and if in doubt, raise a little more, since then you can adjust it with the pedal.
- Prepare the tools to work. You have to extend the tungsten electrode to a diameter similar to that of the nozzle you are going to use. Support the tip of the electrode on the metal piece, and then try to keep it about 3 mm.
- Use the pedal and the torch button to adjust. The torch usually has a button to create the electric arc. So you will need to press it to start welding. If on the contrary, the torch does not have any buttons, you have to create the arc with the pedal. You need to press it halfway. If you can’t create the arc, you probably have to raise the amperage.
- Create the welding puddle. You have to meet the material to create the pool of solder necessary to fill the joint. Go forward through the entire union until you finish welding everything. The disadvantage is that the Aluminium will heat up over time, so you should reduce the amperage so as not to burn the piece as you go along.
- Wait for it to cool. Once you have done the welding of the joint, you must wait for everything to cool.
Weld Aluminium with MIG
MIG welding can also be used to weld Aluminium. It is the most suitable process for thin Aluminium sheets, due to the heat they need.
I leave a video as a warm-up:
The wire feeding system can be a drag, push or drag-push. This will depend on the thickness and hardness of the alloy. In addition, constant voltage power sources with constant speed feeders are used for small diameter wires. In contrast, constant-intensity power sources and variable speed feeders are used for large-diameter wires.
Argon is used as a protective gas, since pure argon is the best gas for MIG welding of Aluminium. As for the transfer gases, different types of transfer can be used, although the transfer that is normally used in MIG welding of Aluminium is usually the transfer of spray or spray.
The technique for welding Aluminium with MIG
The forward welding technique is usually used, tilting the gun about 7º to 12º towards the welding direction.
To turn off the arc, the speed is increased until the electrode is separated from the workpiece, or the other option is to change the welding direction and cut the arc on the welding bead. Appendices can also be used to extinguish the arc over them. Alloys that are bondable are welded with straight strands.
Finally, you should know that MIG welding of Aluminium has some disadvantages, such as imperfections that can be created; such as melting faults, cracks in the crater, porosity and inclusion of oxides.
Weld Aluminium by an electric arc with coated electrode
Aluminium can also be welded by an electric arc, although it is not a highly recommended process because the cord obtained is usually not very homogeneous. But if you need to perform welding where this is not a problem, this type of welding may be an option.
You must keep in mind that the electrodes have to be completely dry and clean to be able to use them without problems, so it is advisable to dry them. In addition, you must preheat the pieces in case they are complicated pieces and of great thicknesses .
And it is that a thickness of 3 mm is minimally recommended to use this welding process on Aluminium . With more than 6 mm, a V chamfer from 60º to 90º must be made, and for large thicknesses, the U preparations are recommended.
After finishing welding, the slag must be removed with a brush and pickaxe, and with the help of hot water. And it is that the slag favours the corrosion of Aluminium.
Weld Aluminium by Oxigas
Aluminium alloys and the Aluminium itself can be welded by Oxigas, but it is recommended to use this process only for minor repairs and welding. Above all, you can use it if the thicknesses of your pieces range between 0.7 and 25 mm.
This process has the advantage of being a very simple process, but it also has a few disadvantages. And, among other things, you have to use a filler material, the process is very slow, deformations occur and it deforms very easily.
The fuel to be used in acetylene with a neutral flame, although sometimes flame with enough acetylene can reduce the formation of oxides.
If the pieces are thicker than 5 mm, single V chamfers are made. They can be made with pieces up to 12 mm. What is not recommended is the use of backing plates or overlapping joints, since the flux can remain there and cause corrosion in the base metal.
If the thickness of the piece is large, a preheat should be performed before welding. To do this, you just have to move the flame circularly and heat the edges of the joint, until the melting bath is formed. There, the contribution metal rod will be placed, and the joint will continue advancing until all the material is melted.
After welding, all remaining flux residue must be removed. To do this, you have to bathe the pieces of water with small amounts of nitric or sulfuric acid, and then wash them with water. Large pieces can also be steam washed.
Weld Aluminium by Strong Welding
Some alloys can be welded by brazing, although the vast majority of alloys cannot be welded by this method. What you have to look to know if you can or not, is the melting temperature of the metal. And it is that many times the melting temperatures of the base metal and the contribution metal are usually very similar, as is the case with Aluminium and copper alloys, and some Aluminium and zinc alloys, such as 7055, 7178 and 7001 (AA)
Aluminium and silicon alloys are normally used as filler metals. To select the correct metal, you must ensure that the melting temperature of the filler material is lower than the base metal. And more if welding is done by a blowtorch.
The paste is applied in the form of a paste, and it is recommended not to use too much, so as not to have problems with corrosion. After welding, you should remove the flux with hot water and a fibre brush, never a wire brush.
Weld Aluminium by Soft Welding
To perform soft welding, a flux is needed to remove the oxide layer and to avoid contact with air among other things.
You always have to eliminate waste from this flux, as they usually absorb moisture. They are removed quite easily with hot water.
The materials that are usually used in the contribution metals are usually tin, zinc, lead and cadmium. But the best mechanical properties are the high-temperature zinc filler metals since they also have very good corrosion behaviour.
People also ask
What kind of welder do you need to weld aluminium?
MIG welding is best for thinner gauges of aluminium sheets because of the amount of heat needed. When choosing a shielding gas, 100 per cent argon is best for MIG welding aluminium. The welder must choose a welding wire or rod that has an alloy as similar to that of the work pieces as possible to create a quality weld.
Is it difficult to weld aluminium?
Aluminium doesn’t act the way other metals do during welding, so it can be difficult to determine weld progress and quality. Simply put, aluminium is difficult to weld because it is a soft, highly sensitive metal insulated by a tougher oxidized layer.
Can you stick weld aluminium?
Can I weld aluminium with a MIG welder?
Aluminium is a tricky metal to weld with a MIG welder because it takes more heat than mild steel (Usually in the range of 21 to 24 volts). When you’re MIG welding mild steel, you can and should move the MIG gun slow enough to get deep penetration.