There are several welding techniques for aluminum alloys, each with its specific uses. In addition to conventional fusion, resistance and gas welding methods, other advanced techniques such as plasma arc welding, electron beam welding and vacuum diffusion welding can also weld aluminum alloys effectively.
1. Common welding methods for aluminum alloy
Common welding methods for aluminum alloys and their respective characteristics and scope of application are presented in Table 1.
Table 1 Characteristics and scope of application of common welding methods for aluminum alloy
| Welding method | Feature | Scope of application |
|---|---|---|
| Gas welding | Low thermal power, large welding deformation, low productivity, easy to produce slag, cracks and other defects | It is used for butt welding and repair welding of thin sheets in non-important occasions |
| Manual arc welding | Poor gasket quality | Used for repair welding and general repair of cast aluminum parts |
| TIG welding | The weld metal is compact, the joint has high strength and good plasticity, and high-quality joint can be obtained | It is widely used and can be welded with plate thickness of 1~20mm |
| Pulsed TIG welding | The welding process is stable, the heat input is accurate and adjustable, the welding deformation is small, and the joint quality is high | Used for sheet metal, all-position welding, assembly welding and high-strength aluminum alloys such as wrought aluminum and duralumin with strong heat sensitivity |
| MIG welding | High arc power and fast welding speed | Can be used to weld thick parts with a thickness of less than 50m |
| MIG Pulsed Argon Arc Welding | Welding deformation is small, porosity and crack resistance is good, process parameters are widely adjustable | It is used for plate or all-position welding and is generally used for workpieces with a thickness of 2~12mm |
| Plasma arc welding | The heat concentration, welding speed, deformation and welding stress are small, the process is more complex | It is used for butt welding where the requirement is higher than argon arc welding |
| Vacuum electron beam welding | The results show that the penetration is large, the heat-affected zone is small, the welding deformation is small, and the mechanical properties of the joint are good. | Used for welding small size welded parts |
| laser welding | Small welding deformation and high productivity | It is used for welding precision parts |
Selection of a welding method for aluminum and aluminum alloys should be based on the quality of the material, the thickness of the component to be welded, the structure of the product and the desired level of weldability.
Related Reading: MIG vs TIG Welding
(1) Gas welding
The thermal power of an oxygen-acetylene welding flame is low, causing heat to be dispersed and resulting in significant welding deformation and low productivity.
When welding thick aluminum welds, preheating is required.
The weld metal produced by this method has a coarse grain and a loose structure, which makes it prone to defects such as alumina inclusion, porosity and cracks.
This welding method should only be used to repair unimportant aluminum structural parts and castings with a thickness of 0.5 to 10 mm.
(2) TIG Welding
This method, known as TIG welding, is performed under argon protection, which results in a more concentrated heat source and stable arc combustion. This results in a denser weld metal with high strength and plasticity, making it widely used in industry.
Although TIG welding is an ideal method for welding aluminum alloys, its equipment is complex, making it less suitable for outdoor operations.
(3) MIG Welding
The automatic and semi-automatic gas metal arc welding (GMAW) process has several advantages, including high arc power, concentrated heat, and a small heat-affected zone. Its production efficiency is 2 to 3 times that of manual GMAW.
GMAW can be used to weld pure aluminum plates and aluminum alloys with a thickness of less than 50 mm. For example, preheating is not necessary for aluminum plates with a thickness of 30 mm, and only the front and back layers need to be welded to obtain a smooth surface and high-quality weld.
Semi-automatic tungsten inert gas (TIG) welding is ideal for precision welding, short and intermittent welding and welding on irregular structures.
Semi-automatic argon arc welding torch provides convenient and flexible welding, but the diameter of the welding wire is smaller and the weld is more prone to porosity.
(4) Pulsed argon arc welding
(1) Pulsed tungsten inert gas (TIG) welding
This method significantly improves the stability of low current welding processes and allows easy control of arc power and weld formation by adjusting various parameters. The weldment has minimal deformation and heat-affected zone, making it ideal for welding thin plates, all-position welding, and welding heat-sensitive materials such as wrought aluminum, hard aluminum, and super-hard aluminum.
(2) Metallic Inert Gas (MIG) Pulse Argon Arc Welding
This method is suitable for all-position welding of aluminum alloy sheets with a thickness of 2 to 10 mm.
(5) Resistance spot welding and seam welding
It can be used to weld aluminum alloy sheets with a thickness of less than 4 mm.
For products with high quality requirements, DC shock wave spot welding and seam welding can be used.
Welding requires sophisticated equipment, high welding currents and high productivity, making it particularly suitable for mass production of parts and components.
(6) Friction stir welding
Friction stir welding (FSW) is a type of solid-state joining technology that can be used to weld various alloy plates.
Compared to traditional fusion welding methods, FSW offers several advantages, such as no spatter, reduced dust, no need for welding wire or shielding gas, and no pores and cracks in the joint.
Furthermore, compared to ordinary friction, FSW is not limited by shaft parts and can produce straight welds.
This welding method also has several other benefits, including improved mechanical properties, energy efficiency, reduced pollution and low preparation requirements before welding.
Due to the low melting point of aluminum and aluminum alloys, FSW is particularly suitable for these materials.
2. Welding materials for aluminum
(1) Welding wire
When welding aluminum alloys using gas welding or TIG welding, it is recommended to use filler wire.
Aluminum and aluminum alloy welding wires can be categorized into two types: homogeneous and heterogeneous.
To obtain a strong and reliable welding joint, it is important to choose the appropriate filler material for the base metal used.
When selecting a welding wire for aluminum alloys, it is important to consider several factors, including the composition requirements, mechanical properties, corrosion resistance, structural rigidity, color and crack resistance of the finished product.
Using a filler metal with a lower melting temperature than the base metal can significantly reduce the risk of intergranular cracking in the heat-affected zone.
For non-heat-treated alloys, weld joint strength increases in the following order: 1000 series, 4000 series, and 5000 series.
It is important to note that 5000 series welding wires containing more than 3% magnesium should not be used in structures with service temperatures above 65°C, as these alloys are highly susceptible to stress corrosion cracking under these conditions.
To avoid cracking, it is often recommended to use a filler metal with a higher alloy content than the base metal.
The most commonly used welding wires for aluminum alloys are standard quality wires with compositions similar to the base metal. In the absence of a standard welding wire, a strip can be cut from the base metal and used as a filler.
A popular choice of welding wire is HS311, which is known for its good flowability, minimal shrinkage during solidification, and excellent crack resistance. To further improve the grain size, crack resistance and mechanical properties of the weld, small amounts of alloying elements such as Ti, V, Zr and others are often added as modifiers.
Attention should be paid to the following issues when selecting aluminum alloy welding wire:
(1) Sensitivity to cracks in solder joints
The main factor affecting crack sensitivity is the compatibility of the base metal and welding wire.
Using a weld metal with a lower melting temperature than the base metal can reduce the cracking sensitivity of both the weld metal and the heat-affected zone.
For example, when soldering alloy 6061 with a silicon content of 0.6%, using the same alloy as the solder results in very high crack sensitivity.
However, the use of ER4043 welding wire with 5% silicon provides good resistance to cracking, as its melting temperature is lower than that of alloy 6061 and it has greater plasticity during cooling.
Furthermore, it is advisable to avoid the combination of Mg and Cu in the weld metal, as Al-Mg-Cu has a high sensitivity to cracking.
(2) Mechanical Properties of Solder Joint
Industrial pure aluminum has the lowest strength, while 4000 series aluminum alloys are in the middle and 5000 series aluminum alloys have the highest strength.
Although Al-Si welding wire has high crack resistance, it has low plasticity.
Therefore, for joints that require plastic deformation processing after welding, it is better to avoid silicone welding wire.
(3) Welded joint performance
The choice of filler metal is not only based on the composition of the base metal, but also on the geometry of the joint, operational corrosion resistance requirements, and appearance requirements of the weldment.
For example, to ensure that a container has good corrosion resistance or to prevent contamination of stored products, a container that stores hydrogen peroxide requires a high-purity aluminum alloy.
In this case, the purity of the filler metal must be at least equal to that of the base metal.
(2) Welding rod
The model, specifications and applications of aluminum alloy welding rod are shown in Table 2. Table 3 shows the chemical composition and mechanical properties of aluminum alloy electrode.
Table 2 Type (brand), specification and application of aluminum and aluminum alloy welding rods
| Types | Note | Skin types | Core material | Electrode specification/mm | Purpose | |
|---|---|---|---|---|---|---|
| E1100 | L109 | Base type | pure aluminum | 3.2,4.5 | 345〜355 | Pure aluminum plate and container welding |
| E4043 | L209 | Base type | Al Si League | 3.2,4.5 | 345〜355 | Aluminum plate for welding, aluminum and silicon casting, general aluminum alloy, forged aluminum, duralumin (except aluminum and magnesium alloy) |
| E3003 | L309 | Base type | Aluminum Manganese Alloy | 3.2,4.5 | 345〜355 | Welding of aluminum manganese alloy, pure aluminum and other aluminum alloys |
Table 3 Chemical composition and mechanical properties of aluminum and aluminum alloy electrodes
| Types | Note | Types of skins | Power supply types | Chemical composition of the solder core/% | Tensile strength of deposited metal / MPa | Tensile strength of welded joint / MPa |
|---|---|---|---|---|---|---|
| E1100 | L109 | Base type | DCEP (direct current electrode positive) | Si+Fe≤0.95,Co0.05〜0.20 Mn≤0.05,Be≤0.0008 Zn≤0.10,others≤0.15 AI≥99.0 | ≥64 | ≥80 |
| E4043 | L209 | Base type | DCEP | Si4.5〜6.0,Fe≤0.8 Cu≤0.30,Mn≤0.05 Zn≤0.10,Mg≤0.0008 others≤0.15,Al Rem. |
≥118 | ≥95 |
| E3003 | L309 | Base type | DCEP | Si≤0.6,Fe≤0.7 Cu0.05〜0.20,Mn1.0 〜1.5 Zn≤0.10, others≤0.15 Al Rem. | ≥118 | ≥95 |
Related Reading: How to Choose the Right Welding Rod?
(3) Shielding gas
The preferred inert gases for welding aluminum alloys are argon and helium.
The technical requirements for argon are a purity level of 99.9% or greater, an oxygen content of less than 0.005%, a hydrogen content of less than 0.005%, a moisture content of less than 0.02 mg/L, and a nitrogen content of less than 0.015%.
An increase in oxygen and nitrogen levels degrades cathodic atomization.
If the oxygen content exceeds 0.3%, the burning loss of the tungsten electrode will intensify, and if the oxygen content exceeds 0.1%, the weld surface will become dull or blackish.
For TIG welding, pure argon is selected for AC plus HF welding, which is suitable for thick plate welding. For DC positive electrode welding, a mixture of Ar + He or pure Air is used.
For plates with a thickness of less than 25 mm, pure argon is used.
For plates with a thickness of 25-50 mm, a mixture of Ar + He with 10% to 35% Ar is used.
For plates with a thickness of 50-75 mm, a mixture of Ar + He with 10% to 35% or 50% He must be used.
For sheets thicker than 75 mm, a mixture of Ar + He with 50% to 75% He is recommended.
3. Aluminum alloy welding process
1. Gas welding of aluminum alloy
The thermal efficiency of oxygen-acetylene gas welding is low and the heat input is not concentrated, making the quality and performance of the joint not high. In addition, flux is required when welding aluminum and aluminum alloys, and residues must be removed after welding.
Despite these disadvantages, gas welding equipment is commonly used to weld aluminum alloys with low quality requirements, such as thin sheets and small parts, as well as to repair aluminum alloys and castings. This is due to its simplicity, lack of need for power supply and its convenient and flexible nature.
(1) Joint form of gas welding
Lap joints and T-joints are not ideal for gas welding of aluminum alloys because it is difficult to remove residual flux and welding slag in the gap. Therefore, it is recommended to use butt joints whenever possible.
To ensure complete welding without collapse or burnout, it is recommended to use a slotted backing plate. The backing plate is typically made of stainless steel or pure copper.
Welding with a backing plate can achieve good reverse forming and improve welding productivity.
(2) Flux selection for gas welding
When gas welding aluminum alloys, the use of flux is necessary to ensure a smooth welding process and good weld quality. Flux, also known as gas flow, removes oxide film and other impurities from the surface of aluminum alloy during welding.
The main function of flux is to remove the oxide film formed on the aluminum surface during welding, improve the wettability of the base metal and promote the formation of a dense weld microstructure.
Flux is typically sprayed directly into the groove of the part to be welded before welding or added to the molten pool of welding wire.
Aluminum alloy fluxes are typically made from chlorides of elements such as potassium, sodium, calcium and lithium. These compounds are ground, sieved, and mixed in specific proportions to create flux.
For example, aluminum cryolite (Na3AlF6) can melt alumina at 1000°C, and potassium chloride can transform refractory alumina into fusible aluminum chloride. Flux has a low melting point and good fluidity, which can also improve the fluidity of molten metal and ensure proper weld formation.
(3) Selection of welding nozzle and flame
Aluminum alloys have a strong tendency to oxidize and absorb air. During gas welding, it is important to use a neutral flame or weak carbonization flame (with excess acetylene) to avoid oxidation of the aluminum. This will keep the pool of molten aluminum under a reducing atmosphere and prevent oxidation.
The use of an oxidation flame is strictly prohibited, as it will strongly oxidize the aluminum and make the welding process difficult.
However, if there is too much acetylene, free hydrogen can dissolve in the molten pool, causing porosity in the weld and loosening it.
(4) Welding point
To avoid changes in size and relative position during welding, pre-spot welding is required.
Gas welding has a high coefficient of linear expansion, fast heat conduction speed and large heating area, so positioning welds must be denser than those for steel parts.
The filler wire used for positioning welding is the same as that used for product welding. Before positioning the weld, a layer of gas flux must be applied to the weld gap.
The flame power during positioning welding should be slightly higher than during gas welding.
(5) Gas welding operation
When welding steel materials, the heating temperature can be determined by observing the color change of the steel. However, this is not possible when welding aluminum alloys as there is no obvious color change during heating.
To control the welding temperature, the welding time can be determined based on the following observations:
- When the surface of the heated part changes from bright white to dull silvery white, with wrinkled surface oxide film and floating metal in the heating area, the melting temperature is about to be reached and welding can be carried out.
- When the end of the welding wire immersed in flux and the heated part can be fused with the original material, the melting temperature has been reached and welding can be carried out.
- When the edge of the base metal falls off, the base metal has reached melting temperature and welding can proceed.
For gas-welded sheets, the left-hand welding method can be used, with the welding wire in front of the welding flame. This helps prevent overheating of the weld pool and grain growth or burning in the heat-affected zone, reducing heat loss.
For base metals thicker than 5mm, the correct welding method can be used, with the welding wire behind the welding torch. This minimizes heat loss, increases melting depth and improves heating efficiency.
When gas welding parts less than 3 mm thick, the torch inclination angle should be 20-40°. For thick parts, the torch inclination angle should be 40-80°, with an angle between the welding wire and the torch of 80-100°.
For gas welding of aluminum alloys, it is best to complete the joint in one pass, as deposition of a second layer may result in slag inclusion in the weld.
(6) Post-welding treatment
Corrosion of aluminum joints caused by residual flux and slag on the gas welding surface is a potential cause of future joint damage.
Within 1-6 hours after gas welding, it is necessary to clean up the residual flux and slag to prevent welding corrosion.
The cleaning process after welding involves the following steps:
- After welding, immerse the welded part in a hot water bath at 40-50°C. It is best to use hot running water and brush the solder, residual flux and slag near the solder with a bristle brush until clean.
- Immerse the solder in a nitric acid solution. When the ambient temperature is above 25°C, the solution concentration should be 15-25% and the soaking time should be 10-15 minutes. When the ambient temperature is 10-15°C, the solution concentration should be 20-25% and the soaking time should be 15 minutes.
- Immerse the welded part in hot water (40-50°C) for 5-10 minutes.
- Rinse the weldment with cold water for 5 minutes.
- Welding can be allowed to air dry or dried in an oven or with hot air.
2. TIG welding of aluminum alloy
Also known as tungsten inert gas (TIG) welding, it involves using tungsten as an electrode to generate an arc between the tungsten and the workpiece. The heat generated by the arc melts the metal to be welded, which is then joined by filler wire to form a solid welding joint.
Argon arc welding of aluminum uses the “cathodic atomization” properties of argon to remove the oxide film from the surface.
The TIG welding process protects the tungsten electrode and the welding area by shielding them with an inert gas, such as argon, which is emitted from the nozzle. This helps to avoid any reaction between the welding area and the surrounding air.
The TIG welding process is ideal for welding thin plates with a thickness of less than 3mm. This results in less deformation of the part compared to gas welding and manual arc welding.
The AC TIG welding method is particularly useful for welding aluminum alloys as the cathode can remove the oxide film and prevent corrosion. This results in a shiny, smooth surface with an unrestricted joint shape. The argon flow also cools the joint quickly, improving its microstructure and properties, making it suitable for welding in all positions.
However, the TIG welding process requires more rigorous cleaning before welding due to the absence of flux. AC TIG welding and AC pulse TIG welding are the preferred methods for welding aluminum alloys, followed by DC reverse TIG welding.
In general, AC welding is most commonly used for aluminum alloys as it provides the best combination of current carrying capacity, arc control and cleanliness. When DC positive connection (electrode connected to negative electrode) is used, the heat generated on the workpiece surface results in deep penetration and a higher welding current can be used for a given electrode size.
This method does not require preheating even for thick sections and causes minimal deformation of the base metal. However, the DC reverse connection (electrode to positive electrode) TIG welding method is rarely used for welding aluminum. Despite this, it offers advantages such as shallow melting depth, easy arc control and good purification effects for continuous welding or repair welding of thin-walled heat exchangers and similar components with tube thickness less than 2.4mm.
(1) Tungsten electrode
The melting point of tungsten is 3410°C.
Tungsten has strong electron emission ability at high temperatures.
By adding trace amounts of rare earth elements such as thorium, cerium and zirconium, the electron emission efficiency is significantly decreased and the current carrying capacity is significantly improved.
In TIG welding of aluminum alloys, a tungsten electrode is mainly used to conduct current, start an arc and maintain normal arc combustion.
Commonly used tungsten electrode materials include pure tungsten, thorium-tungsten and cerium-tungsten.
(2) Welding process parameters
To obtain excellent weld formation and quality, welding process parameters must be selected based on the technical requirements of welding.
The main process parameters for manual TIG welding of aluminum alloys include current type, polarity, current size, shielding gas flow rate, tungsten electrode extension length, and distance between nozzle and workpiece.
Process parameters for automatic TIG welding also include arc voltage (arc length), welding speed, and wire feed speed.
Depending on the material and thickness to be welded, process parameters will include tungsten electrode diameter and shape, welding wire diameter, type of shielding gas, gas flow rate, nozzle diameter, welding current, arc voltage, welding speed and these parameters can be adjusted based on actual welding results until they meet the desired requirements.
The following are the main considerations for selecting TIG welding parameters for aluminum alloy:
- Nozzle diameter and shielding gas flow: The nozzle diameter for aluminum alloy TIG welding is typically 5 to 22 mm, while the shielding gas flow rate is generally 5 to 15 l/min.
- Tungsten electrode length and nozzle-workpiece distance: For butt welds, the tungsten electrode extension length is normally 5 to 6 mm, while for fillet welds it is 7 to 8 mm. The distance between the nozzle and the workpiece is generally around 10 mm.
- Welding current and voltage: Welding current and voltage are related to factors such as plate thickness, joint type, welding position, and welder skill level. In manual TIG welding, when using AC power and welding with a thickness of less than 6 mm, the maximum welding current can be calculated by the formula I = (60 ~ 65) d, where D is the diameter of the electrode. The arc voltage is mainly determined by the arc length, which should be approximately equal to the diameter of the tungsten electrode.
- Welding speed: To minimize deformation during TIG welding of aluminum alloy, a faster welding speed should be used. In manual TIG welding, the welder adjusts the speed as needed based on the size and shape of the weld pool and the melting conditions on both sides. The general welding speed is 8-12 m/h, while in automatic TIG welding the speed remains constant once the process parameters are defined.
- Wire diameter: The diameter of the welding wire is generally proportional to the thickness of the plate and the welding current.
Common Defects and Causes of Aluminum Welding
Causes of stomata closure
- Impurities in the argon gas supply or leaks in the argon piping
- Inadequate cleaning of the welding wire or base metal groove before welding or contamination after cleaning
- Incorrect welding current or speed
- Poor weld pool protection, unstable arc, prolonged arc length, or excessive tungsten electrode extension.
Preventive measures:
- Ensure purity of argon gas supply by thoroughly cleaning piping and welding wire, and prevent recontamination by welding immediately after cleaning.
- Upgrade the gas supply pipeline, choose the appropriate gas flow rate, and adjust the tungsten electrode extension length as needed.
- Correctly select the welding process parameters.
- Consider using a preheating process and installing windproof devices at the welding site to prevent wind interference.
Causes of Weld Cracks
- Incorrect selection of welding wire alloy composition
- Insufficient magnesium content in the solder (less than 3%) or excessive impurities such as iron and silicon
- High melting temperature of welding wire leading to liquefaction cracks in the heat affected zone
- Inadequate joint design, excessive welding concentration, or excessively high temperature in the heating zone causing excessive restraint stress
- High levels of turbulence, prolonged exposure time, or tissue overheating
- Unfilled craters resulting in cracks.
Preventive measures:
- Make sure the composition of the welding wire matches that of the base metal.
- Use an arc impingement plate or current attenuation device to fill the arc pit.
- Properly design the welding structure, arrange welding seams reasonably, avoid stress concentrations, and choose the appropriate welding sequence.
- Adjust the welding current or increase the welding speed as needed.
Causes of Incomplete Weld Penetration
- Fast welding speed, long arc length, small welding gap, angle or current or large blunt edge
- Presence of burrs on the edge of the groove or dirt on the lower edge of the part
- Incorrect inclination angle between welding torch and welding wire
Preventive measures:
- Correctly select the gap, blunt edge, groove angle and welding process parameters.
- Thoroughly clean the oxide film, flux, slag and oil.
- Improve welding technique.
Causes of tungsten inclusion in weld
- Contact arc
- Improper tungsten electrode tip shape or excessive welding current leading to electrode detachment
- Improper use of oxidizing gas causing the filler to touch the hot tip of the tungsten electrode
Preventive measures:
- Use high-frequency, high-voltage pulsed arc ignition.
- Choose the appropriate shape for the tungsten electrode tip based on the selected current.
- Reduce the welding current, increase the tungsten electrode diameter or decrease its length.
- Replace inert gas.
- Improve welding technique and avoid contact between filler wire and tungsten electrode.
Causes of Undercutting
- Large welding current, high arc voltage, irregular torch oscillation, insufficient wire filling, or fast welding speed
Preventive measures:
- Reduce welding current and arc voltage, maintain uniform torch oscillation, increase wire feed speed or reduce welding speed as appropriate.
4. Conventional repair welding process of castings
Defects in aluminum alloy castings can usually be repaired using argon arc welding, with best results using AC TIG welding.
When using repair welding to correct casting defects, it is important to clean the welding wire and parts before welding, select appropriate welding wire materials, and use short arc and small angle welding wire. In practice, there have been many successful experiences with different types of defects, such as using low welding current whenever possible.
The welding wire must have a higher alloy composition than the base metal to supplement any alloy burned during repair welding and maintain consistency in weld composition.
For castings with crack defects, holes must be drilled to prevent cracks at both ends before repair welding. The part should be preheated and welded using a left hand welding method to observe the weld melting. The wire must be filled to form a fully wet weld pool.
When the defect is large, a thin layer of surfactant (ATIG surfactant) can be applied to the welding position to increase efficiency during traditional TIG welding. Surfactant causes the welding arc to shrink or the metal flow in the weld pool to change, resulting in greater weld penetration.
In AC TIG welding of aluminum alloy, a layer of SiO2 active agent can be applied to the weld surface to change penetration, reduce preheating and facilitate the welding process.
5. Features of welding aluminum and aluminum alloys
(1) Aluminum is highly subject to oxidation in air and during welding, forming aluminum oxide (Al2O3) which has a high melting point and is very stable, making it difficult to remove. This makes it difficult to melt and melt the base material. The heavy oxide film does not emerge easily, leading to slag inclusions, incomplete melting and insufficient penetration.
The surface oxide film of aluminum and the large amount of adsorbed moisture can cause porosity in the weld. Before welding, rigorous cleaning of the surface must be carried out using chemical or mechanical methods to remove this oxide film. Protection must be reinforced during the welding process to avoid oxidation. When using tungsten inert gas welding, an alternating current source must be selected to remove the oxide film through “cathodic cleaning”.
In gas welding, a flux must be used to remove the oxide film. When welding thick plates, the welding heat can be increased. For example, the heat of the helium arc is high, so helium or argon-helium mixed gas shielding may be used, or large specification gas shielded arc welding may be employed. In the case of positive direct current connection, “cathodic cleaning” is not necessary.
(2) The thermal conductivity and specific heat capacity of aluminum and aluminum alloys are more than twice those of carbon steel and low-alloy steel. The thermal conductivity of aluminum is tens of times greater than that of austenitic stainless steel.
During the welding process, a large amount of heat can be quickly conducted to the base metal, therefore, when welding aluminum and aluminum alloys, in addition to the energy consumed in melting the metal pool, more heat is wasted on other parts of the metal. This energy waste is more significant than in steel welding.
To obtain high-quality welded joints, energy sources with concentrated energy and high power should be used as much as possible. Sometimes preheating and other process measures can also be adopted.
(3) The coefficient of linear expansion of aluminum and its alloys is approximately twice that of carbon steel and low-alloy steel. Aluminum undergoes significant volume contraction after solidification, leading to considerable deformation and stress in the weld, necessitating measures to prevent weld deformation. Aluminum weld pools are prone to shrinkage holes, porosity, hot cracking, and high internal stress during solidification.
In production, adjusting the composition of the welding wire and the welding process can prevent the occurrence of hot cracks. Aluminum silicon alloy welding wire can be used to weld aluminum alloys except aluminum magnesium alloys where corrosion resistance is permitted. In aluminum and silicon alloys, the tendency to hot cracking is greater when the silicon content is 0.5%.
As the silicon content increases, the crystallization temperature range of the alloy decreases, the fluidity improves significantly, the shrinkage rate decreases, and the tendency to hot cracking reduces correspondingly. Based on production experience, hot cracking does not occur when the silicon content is 5% to 6%. Therefore, using SAlSi rods (with silicon content between 4.5% and 6%) for welding can result in better crack resistance.
(4) Aluminum has strong light and heat reflectivity. There is no noticeable color change during the solid-liquid transition, making it difficult to judge during welding operations. High-temperature aluminum has low strength, making it difficult to support the weld pool and easy to burn.
(5) Liquid aluminum and its alloys can dissolve a large amount of hydrogen, while solid aluminum hardly dissolves it. During the solidification and rapid cooling of the welding pool, hydrogen does not have enough time to escape, easily leading to the formation of hydrogen pores. Moisture in the arc column atmosphere, welding materials, and moisture adsorbed by the surface oxide film of the parent material are critical sources of hydrogen in the weld seam. Therefore, hydrogen sources must be strictly controlled to prevent pore formation.
(6) Alloying elements tend to evaporate and burn, causing a decrease in weld seam performance.
(7) If the base metal of the original material is deformed or strengthened by solution aging, the heat of welding may reduce the strength of the heat-affected zone.
6. Mission Completion
TIG and MIG arc welding, which is convenient and economical, can be used for welding and repairing aluminum alloys.
When high-energy beam welding and friction welding are used in aluminum alloy welding, the problems of alloy element burning, joint softening and welding deformation can be solved effectively. Friction welding, in particular, is a solid-state connection that has the added benefits of being environmentally friendly.
When conventional repair welding methods are used to repair defects in aluminum alloy castings, it is important to pay attention to cleaning before welding, selecting a suitable welding wire filler, and following the correct welding process specifications. AC TIG repair welding is typically preferred to avoid welding defects.
In order to improve the quality of repair welding of aluminum alloy castings, special repair welding methods can be used in combination with the actual situation when casting defects are unique and conditions permit.
