Welding Materials for Aluminium
(1) Welding wire
When welding aluminum alloys by gas welding and argon tungsten arc welding, it is necessary to add filler wire. Aluminum and aluminum alloy welding wires are divided into two categories: homogeneous welding wires and heterogeneous welding wires. In order to obtain a good welded joint, the welding wire suitable for the base metal should be selected as the filler material considering the use requirements of the welded components.
The composition requirements of the welding seam, the mechanical properties, corrosion resistance of the product, rigidity, color and crack resistance of the structure should be considered for selecting welding wires. Selecting a filler metal with a melting temperature lower than that of the base metal can greatly reduce the tendency for intergranular cracking in the heat-affected zone. The welded joint strength of non-heat-treated alloys should be increased in the order of series 1000, series 4000, and series 5000.
Series 5000 welding wires containing more than 3% magnesium should not be used in structures with operating temperatures above 65℃, because these alloys are very sensitive to stress corrosion cracking; stress corrosion cracking will occur in the above-mentioned temperature and corrosive environment. Using a welding wire whose alloy content is higher than the base metal as the filler metal usually prevents the cracking tendency of the welding seam's metal.
At present, most of the commonly used welding wires for aluminum alloys are welding wires with standard grades that have a similar composition to the base metal. In the absence of welding wires with standard grades, strips can be cut from the base metal. The more common welding wire is HS311, which has good liquid metal fluidity, small shrinkage during solidification, and excellent crack resistance. To refine grains and improve the crack resistance and mechanical properties of the welding seam, a small amount of Ti, V, Zr and other alloying elements are usually added to the welding wire as modificators.
The problems that should be paid attention to when choosing aluminum alloy welding wires are as follows:
Crack sensitivity of welded joints
The direct factor that affects the crack sensitivity is the matching of the base metal and the welding wire. Selecting a welding seam metal with a melting temperature lower than that of the base metal can reduce the crack sensitivity of the welding seam metal and heat-affected zone. For example, when welding 6061 alloys with a silicon content of 0.6% and the same alloy is used as the welding seam, the crack sensitivity is great.
However, the ER4043 welding wire with a silicon content of 5% has good crack resistance due to its lower melting temperature than that of the 6061 alloy and higher plasticity during cooling. In addition, avoids the combination of magnesium and copper for the welding seam metal, because Al-Mg-Cu has great crack sensitivity.
Mechanical properties of welded joints
Industrial pure aluminum has the lowest strength; series 4000 aluminum alloy's strength is average, and series 5000 aluminum alloys have the highest strength. Although aluminum silicon welding wire has good crack resistance, the plasticity of welding wires containing silicon is poor. Welding wires containing silicon should be avoided for joints that need plastic deformation after welding.
The performance of welded joints
The choice of filler metal depends not only on the base metal's composition, but also on the geometry of the joint, the requirement of corrosion resistance in service, and the appearance of the weldment. For example, welded containers for storing hydrogen peroxide require aluminum alloys with high purity to provide good corrosion resistance to the container or to prevent contamination from the stored product. In this case, the purity of the filler metal must be at least equivalent to the base metal.
(2) Welding rods
See Table 2 for the model, specification and uses of aluminum alloy welding rods. The chemical composition and mechanical properties of the aluminum alloy welding rods are shown in Table 3.
Table 2 Grades, specifications and uses of aluminum and aluminum alloy welding rods
When welding aluminum alloys by gas welding and argon tungsten arc welding, it is necessary to add filler wire. Aluminum and aluminum alloy welding wires are divided into two categories: homogeneous welding wires and heterogeneous welding wires. In order to obtain a good welded joint, the welding wire suitable for the base metal should be selected as the filler material considering the use requirements of the welded components.
The composition requirements of the welding seam, the mechanical properties, corrosion resistance of the product, rigidity, color and crack resistance of the structure should be considered for selecting welding wires. Selecting a filler metal with a melting temperature lower than that of the base metal can greatly reduce the tendency for intergranular cracking in the heat-affected zone. The welded joint strength of non-heat-treated alloys should be increased in the order of series 1000, series 4000, and series 5000.
Series 5000 welding wires containing more than 3% magnesium should not be used in structures with operating temperatures above 65℃, because these alloys are very sensitive to stress corrosion cracking; stress corrosion cracking will occur in the above-mentioned temperature and corrosive environment. Using a welding wire whose alloy content is higher than the base metal as the filler metal usually prevents the cracking tendency of the welding seam's metal.
At present, most of the commonly used welding wires for aluminum alloys are welding wires with standard grades that have a similar composition to the base metal. In the absence of welding wires with standard grades, strips can be cut from the base metal. The more common welding wire is HS311, which has good liquid metal fluidity, small shrinkage during solidification, and excellent crack resistance. To refine grains and improve the crack resistance and mechanical properties of the welding seam, a small amount of Ti, V, Zr and other alloying elements are usually added to the welding wire as modificators.
The problems that should be paid attention to when choosing aluminum alloy welding wires are as follows:
Crack sensitivity of welded joints
The direct factor that affects the crack sensitivity is the matching of the base metal and the welding wire. Selecting a welding seam metal with a melting temperature lower than that of the base metal can reduce the crack sensitivity of the welding seam metal and heat-affected zone. For example, when welding 6061 alloys with a silicon content of 0.6% and the same alloy is used as the welding seam, the crack sensitivity is great.
However, the ER4043 welding wire with a silicon content of 5% has good crack resistance due to its lower melting temperature than that of the 6061 alloy and higher plasticity during cooling. In addition, avoids the combination of magnesium and copper for the welding seam metal, because Al-Mg-Cu has great crack sensitivity.
Mechanical properties of welded joints
Industrial pure aluminum has the lowest strength; series 4000 aluminum alloy's strength is average, and series 5000 aluminum alloys have the highest strength. Although aluminum silicon welding wire has good crack resistance, the plasticity of welding wires containing silicon is poor. Welding wires containing silicon should be avoided for joints that need plastic deformation after welding.
The performance of welded joints
The choice of filler metal depends not only on the base metal's composition, but also on the geometry of the joint, the requirement of corrosion resistance in service, and the appearance of the weldment. For example, welded containers for storing hydrogen peroxide require aluminum alloys with high purity to provide good corrosion resistance to the container or to prevent contamination from the stored product. In this case, the purity of the filler metal must be at least equivalent to the base metal.
(2) Welding rods
See Table 2 for the model, specification and uses of aluminum alloy welding rods. The chemical composition and mechanical properties of the aluminum alloy welding rods are shown in Table 3.
Table 2 Grades, specifications and uses of aluminum and aluminum alloy welding rods
| Models | Grades | Coatings | Core wire materials | models Specifications of welding rods/mm |
Uses | |
| E1100 | L109 | The basic type | Pure aluminum | 3.2 and 4.5 | 345 to 355 | Welding pure aluminum plates and pure aluminum containers |
| E4043 | L209 | The basic type | Aluminum silicon alloys | 3.2 and 4.5 | 345 to 355 | Welded aluminum plates, aluminum silicon castings, general aluminum alloys, forged aluminum and hard aluminum (except aluminum magnesium alloys) |
| E3003 | L309 | The basic type | Aluminum manganese alloys | 3.2 and 4.5 | 345 to 355 | Welding aluminum manganese alloys, pure aluminum and other aluminum alloys |
Table 3 Chemical composition and mechanical properties of aluminum and aluminum alloy welding rods
| Models | Grades | Coatings | Type of power supply | The chemical composition of core wire/% | Tensile strength of deposited metal/MPa | Tensile strength of welded joints/MPa |
| E1100 | L109 | The basic type | Direct current reverse polarity | Si+Fe is less than and equal to 0.95. Co is between 0.05 and 0.20. Mn is less than and equal to 0.05. Be is less than and equal to 0.0008. Zn is less than and equal to 0.10, and the other total amount is less than and equal to 0.15. AI is greater than and equal to 99.0. | Greater than and equal to 64 | Greater than and equal to 80 |
| E4043 | L209 | The basic type | Direct current reverse polarity | Si is between 4.5 and 6.0. Fe is less than and equal to 0.8. Cu is less than and equal to 0.30. Mn is less than and equal to 0.05. Zn is less than and equal to 0.10. Mg is less than and equal to 0.0008. The rest of the amount is less than and equal to 0.15. Al is the rest. | Greater than and equal to 118 | Greater than and equal to 118 |
| E3003 | L309 | The basic type | Direct current reverse polarity | Si is less than and equal to 0.6 and Fe 0.7. Cu is from 0.05 to 0.20 and Mn 1.0 to 1.5. Zn is less than and equal to 0.10, and the rest is less than and equal to 0.15. Al is the rest. | Greater than and equal to 95 | Greater than and equal to 95 |
(3) Protective gases
Inert gases for welding aluminum alloys include argon and helium. The technical requirements of argon are that Ar is greater than 99.9%, oxygen less than 0.005%, hydrogen 0.005%, moisture 0.02mg/L and nitrogen 0.015%. Oxygen and nitrogen increase, and both deteriorate the cathode atomization. Oxygen being greater than 0.3% will aggravate the burning loss of tungsten electrode, and if it exceeds 0.1%, the surface of the welding seam will be dull or black.
In tungsten argon arc welding, pure argon gas is used for AC and high-frequency welding, which is suitable for plates with great thickness. Ar plus He or pure Ar is used for DC positive polarity welding.
In melting electrode argon arc welding, when the plate's thickness is less than 25mm, pure Ar is used. When the plate thickness is 25 to 50 mm, an Ar plus He mixed gas added with 10% to 35% Ar is used. When the plate thickness is 50 to 75 mm, it is advisable to use an Ar plus He mixed gas with 10% to 35% or 50% He. When the plate thickness is greater than 75mm, it is recommended to use an Ar plus He mixed gas added with 50% to 75% He.
