Aluminum welding process

I’ve gathered some information for the original poster’s reference. I hope this can be helpful to you. 1. Welding characteristics of aluminum (1) Aluminum oxidizes very easily in air and during welding; the resulting alumina (Al2O3) has a high melting point and is highly stable, making it difficult to remove. It hinders the melting and fusion of the base material; due to its high density, the oxide film does not easily rise to the surface, leading to defects such as inclusions, lack of fusion, and incomplete welding. The surface oxide film of aluminum absorbs a large amount of moisture, which can easily cause pores in the welds. Before welding, strict surface cleaning using chemical or mechanical methods should be carried out to remove the oxide film from the surface. Enhance protection during the welding process to prevent oxidation. In TIG welding, an AC power source is used to remove the oxide film through the effect of \"cathode cleaning\". During gas welding, a flux that removes the oxide film is used. When welding thick plates, it is possible to increase the welding heat input; for example, helium arcs generate a high amount of heat, and protection can be provided using helium or a mixture of argon and helium. Alternatively, GMAW with larger wire gauges can be employed, and in the case of DC positive polarity, \"cathode cleaning\" is not required. 　　(2) The thermal conductivity and specific heat capacity of aluminum are both more than twice those of carbon steel and low-alloy steel. The thermal conductivity of aluminum is more than a dozen times that of austenitic stainless steel. During the welding process, a large amount of heat is quickly conducted into the base metal. Therefore, when welding aluminum, in addition to being used to melt the metal pool, more heat is wasted in other parts of the metal. This unnecessary loss of energy is more significant compared to welding steel. To obtain high-quality welds, it is advisable to use energy sources that provide concentrated power; sometimes preheating and other technical measures can also be employed. 　　(3) The linear expansion coefficient of aluminum is about twice that of carbon steel and low-alloy steel. Aluminum experiences a large volume contraction during solidification, resulting in significant deformation and stress in the welded joints; therefore, measures must be taken to prevent welding deformation. During the solidification of the aluminum welding pool, shrinkage cavities, porosity, thermal cracks, and high internal stresses tend to occur. In production, measures such as adjusting the wire composition and welding parameters can be employed to prevent the occurrence of hot cracks. Where corrosion resistance permits, aluminum-silicon alloy welding wires can be used to weld aluminum alloys other than aluminum-magnesium alloys. In aluminum-silicon alloys, the tendency to undergo thermal cracking is high when the silicon content is 0.5%. As the silicon content increases, the crystallization temperature range of the alloy decreases, its fluidity improves significantly, the shrinkage rate drops, and the tendency to thermal cracking also decreases accordingly. Based on production experience, thermal cracking does not occur when the silicon content is 5%–6%; therefore, using SAlSi wire (with a silicon content of 4.5%–6%) provides better crack resistance. 　　(4) Aluminum has a strong ability to reflect light and heat; there is no significant change in color during the solid-liquid phase transition, making it difficult to judge during welding operations. Aluminum has very low strength at high temperatures, making it difficult to support the molten pool and prone to weld penetration. 　　(5) Aluminum can dissolve a large amount of hydrogen in its liquid state, but it hardly dissolves hydrogen in its solid state. During the solidification and rapid cooling of the welding pool, hydrogen does not have time to escape, making it very easy for hydrogen pores to form. The moisture in the arc column atmosphere, as well as the moisture adsorbed on the surface oxide films of the welding materials and base metal, are all important sources of hydrogen in the weld. Therefore, the source of hydrogen must be strictly controlled to prevent the formation of pores. 　　(6) When the base metal of the base material is strengthened by deformation or solid solution aging, the welding heat will reduce the strength of the heat-affected zone. 　　(7) Aluminum has a face-centered cubic crystal structure; it has no allotropes, and no phase changes occur during heating or cooling. The grain size in welds tends to become coarse, and it is not possible to refine the grains through phase changes. 　　 2. Welding methods Almost all welding methods can be used to weld aluminum, but aluminum responds differently to various welding methods, and each method has its own appropriate applications. Gas welding and shielded metal arc welding are methods with simple equipment and easy operation. Oxyacetylene welding can be used for patch welding thin aluminum sheets and castings where high welding quality is not required. Shielded metal arc welding can be used for patch welding aluminum alloy castings. Gas shielded welding (TIG or MIG) is the most widely used welding method for aluminum and aluminum alloys. Aluminum and aluminum alloy thin sheets can be welded using tungsten inert gas arc welding with alternating current or tungsten inert gas arc welding with pulsed current. Thick plates of aluminum and aluminum alloys can be welded using tungsten inert gas welding, argon-helium mixed tungsten inert gas welding, metal inert gas welding, and pulsed metal inert gas welding. GMAW and pulsed GMAW are being used more and more widely (with argon or an argon/helium mixture).

Request the welding procedure qualification for aluminum from the construction contractor; it specifies the welding parameters for aluminum. This is a technical document that the construction party must provide prior to welding, and it constitutes the internal technical resources of each company.

Our company has just built several aluminum storage tanks; the welding quality is acceptable. The specific welding materials used are pure aluminum 1060(0), 1060(H112), and aluminum-magnesium alloy 5052(0), 5052(H112). Feel free to contact me if you need any further information

QB Sinopec Group Enterprise (General Processes) Standards, Fourth Construction Company ★Piping Engineering★ QJ/PG (Welding) -08 General Construction Procedures for Welding Aluminum and Aluminum Alloys in Industrial Pipelines. Published on October 1, 1999; implemented on January 1, 2000. Issued by the Technical Department of Sinopec Group’s Fourth Construction Company. General Construction Procedures for Welding Aluminum and Aluminum Alloys in Industrial Pipelines 1 Scope of application: These procedures are applicable to the welding of pipes made of industrial pure aluminum and rust-resistant aluminum alloys in projects undertaken by FCC, with the welding methods being manual tungsten inert gas welding and metal inert gas welding. 2 Construction preparation: 2.1 Material requirements 2.1.1 The construction site should be equipped with a fixed or mobile electrode storage area that meets the required standards. 2.1.2 Welding materials must be accompanied by a quality certificate or material certification; their storage, issuance, and retrieval shall be carried out in strict accordance with the relevant provisions outlined in the \"Pressure Pipeline Quality Manual\". 2.1.3 The base material and welding wire shall be properly stored to prevent damage, contamination, and corrosion. 2.1.4 Surface cleaning of welding wire 1) For welding wire that has already been cleaned by the manufacturer and delivered in sealed boxes, it should be dried at 80~100°C before use to remove moisture from its surface. Care must be taken to prevent contamination during use; otherwise, the surface oil and oxide layers need to be removed. 2) For wire delivered in bulk or with an untreated surface, the oil and oxide films on its surface should be removed before use. 3) Oil stains are removed using organic solvents such as acetone or carbon tetrachloride, while oxide films are removed by chemical methods. The sequence of chemical cleaning is shown in the table below: Cleaning sequence: 1, 2, 3, 4, 5, 6. Process names: Degreasing, Alkali washing, Rinsing, Neutralization and passivation, Rinsing, Drying. Concentration of NaOH solution: %; Temperature: °C; Time: minutes. Concentration of HNO3 solution: %; Temperature: °C; Time: minutes. For pure aluminum: Propanone or similar organic solvents; Temperature: 13–18 °C; Time: 10–15 minutes. For water: Temperature: 25–30 °C; Time: 1–3 minutes. Drying is done using oil-free compressed air or at room temperature for 5–10 minutes. For rust-resistant aluminum: Temperature: 50–60 °C; Time: 5–10 minutes. 4) After chemical cleaning, the welding wire must be free of any traces of water or alkali; otherwise, it needs to be cleaned again. 5) The cleaned welding wire should be kept free from contamination before welding, and welding must be carried out within eight hours; otherwise, it needs to be cleaned again. 2.2 Equipment Requirements 2.2.1 For manual TIG welding, an AC manual TIG welding machine should be used. The welder features good high-frequency arc initiation and arc stabilization capabilities, enabling it to achieve a steep voltage drop characteristic and sufficient current capacity. It features flexible adjustment and safe, reliable performance. 2.2.2 For gas metal arc welding with a melting electrode, a DC power supply equipped with a constant-speed wire feeding system and constant current capability is generally used. Commonly, the American Lincoln DC-400 or DC-600 multi-functional power supplies are used in combination with LN-9 or LN-9GMA wire feeders, or the Lincoln Inverter-300 power supply is used together with an LN-9 wire feeder. 2.2.3 Cerium-tungsten or thorium-tungsten electrodes should be used for the tungsten electrode, and the tip of the tungsten electrode is ground into a spherical shape before use. 2.2.4 The stainless steel wire brushes used for welding, as well as the grinding machines and electric stainless steel wire brushes, are all properly prepared. 2.3 Operating Conditions: 2.3.1 Personnel Qualifications: Welders must pass examinations in accordance with the relevant provisions of the \"Code for Construction and Acceptance of Welding Works on On-site Equipment and Industrial Piping\" GB50236-98, and obtain a welder’s certificate valid for the corresponding welding methods; or they may take examinations in accordance with ASME Volume IX. 2.3.2 Environmental conditions: Before welding, it is necessary to ensure that the environment meets the following requirements: 1) Wind speed should be less than 2 m/s. 2) Ambient temperature should be at least 5°C. 3) Relative humidity should not exceed 80%. 4) The welding area must be kept clean, separated from areas where other materials such as carbon steel are being worked on, and it should have wind and rain protection facilities. 3 Welding 3.1 Welding procedures 3.2 Grooves 3.2.1 Types of grooves 3.2.1.1 Types of grooves for manual TIG welding are shown in the table below: Thickness T (mm) Groove name Type of groove Groove dimensions Remarks Gap C (mm) Bevel length p (mm) Groove angle α 8 U-shaped αc p 0~2.5 1.5~2.5 55~65 The radius of curvature at the root of the U-shaped groove is 6~8 mm. >814 X-shaped groove αc 0~2 2~3 75°±5° R=4~6 When it is 5 mm, this value should not exceed 10% of the wall thickness, and it should also not be more than 2 mm. 3.3 Welding methods 1) Manual TIG welding is used for butt joints of pipes under 10″ and for the fillet welds of all pipeline connections. 2) The butt welding of pipes over 10″, as well as the support and reinforcement plates for all pipelines, shall be carried out using the gas tungsten arc welding method. 3.4 Spot Welding: Manual TIG welding is used for spot welding, with a bridge-type welding method. The process and welding materials are the same as those used in regular welding. The number of weld points ranges from 3 to 5, and the thickness of each weld point is 70% of the wall thickness, with a maximum thickness of 6 mm. 3.5 Key points for welding: 1) Before actual welding, a surfacing test should be conducted on a test plate; all process parameters must be adjusted, and it is necessary to confirm the absence of pores before proceeding with welding. 2) Each weld joint must be welded continuously in one go. 3) Rolling welding should be preferred for the welding position to ensure weld quality. 4) When performing multi-layer welding, it is advisable to reduce the number of welding layers; the interlayer temperature should be as low as possible, not exceeding 65°C. Impurities such as alumina present between the layers must be removed mechanically. 5) Under the condition of ensuring proper weld penetration and fusion, a high current and fast welding speed should be used as much as possible within the limits permitted by the welding procedure specification; the lateral movement of the welding wire should not exceed 3 times its diameter. 6) For GMAW, a droplet transfer mode of jet transfer is recommended, and the arc and voltage should be set at slightly lower values. 7) The end of the welding wire in manual TIG welding should not leave the argon shield; the angle between the welding wire and the weld surface should be 15 degrees, while the angle between the welding torch and the weld surface should be 80–90 degrees. 8) During welding, the oxide films between weld layers, excess weld metal, and other welding defects must be removed. For welds that require root cleaning in double-sided welding or for root sealing welding, mechanical methods should be used to clean the weld roots. 4 Welding Precautions and Requirements 4.1 The welding wire used for TIG welding should be stored in a wire box after cleaning, to be retrieved as needed. 4.2 When the tip of the tungsten exhibits contamination or irregular shapes, it must be repaired or replaced. 4.3 Arc starting and arc scraping on the pipe surface at non-welding areas are prohibited. 4.4 When starting arc welding with a tungsten inert gas welder, it is necessary to avoid contact between the tungsten electrode and the base material; during welding, care should be taken to ensure that the welding wire does not come into contact with the tungsten electrode. 4.5 When there is spatter attached to the nozzle that significantly hinders the flow of argon gas, the spatter must be removed or the nozzle replaced. 4.6 The welding wire should be properly stored to prevent it from getting damp. 4.7 In GMAW, the wire feeding sleeve and wire feeding wheel in the welding gun should be cleaned and purged regularly, and the wire feeding sleeve should be replaced if necessary. 4.8 Aluminum and aluminum alloy welds suffer from significant shrinkage deformation; therefore, the tack welds must have sufficient length, spacing, and height to ensure adequate strength and prevent cracking during welding. 4.9 After welding is completed, the surface of the weld must be thoroughly cleaned. Once the visual inspection of the weld shows it to be satisfactory, the welder shall mark a steel stamp at a distance of 30–50 mm from the weld. 4.10 Tungsten inert gas welding welders should wear clean white gloves when operating to feed the welding wire. 4.11 For welds that use temporary shims, the shims must not be melted during welding; if they do melt into the weld, that portion of the weld must be removed promptly before welding can continue. 5 Weld Repair 5.1 Weld repair should be carried out by certified welders who possess the appropriate qualifications for such work. 5.2 Before rework, the type of defect should be identified, the causes of the defect analyzed, and the location of the defect determined. 5.3 Defect removal method: Grinding is carried out using a grinder. After the defects are removed, the repaired area should be prepared by creating bevels, and stainless steel wire brushes are used to remove any powder from the defect area prior to welding. 5.4 The number of rework attempts for the same area should not exceed 2 times; for welds that fail after two rework attempts, they should be cut out and rewelded. 6 Quality Standards 6.1 The weld shall transition smoothly to the surface of the base material; its surface must be free from defects such as cracks, lack of fusion, pores, oxide inclusions, and overheating. 6.2 Weld bead height: when the base metal thickness T is ≤ 10 mm, it shall not exceed 3 mm; when T > 10 mm, it shall not exceed 1/3T, with a maximum value of 5 mm. 6.3 Weld undercut depth: When the base metal thickness T is ≤ 10 mm, it shall not exceed 0.5 mm; when T > 10 mm, it shall not exceed 0.8 mm. The total length of undercuts on both sides of the weld shall not exceed 20% of the total length of the weld. 6.4 Surface depressions: Except that on the inner surface of the single-sided weld in the overhead welding position, depressions with a depth not exceeding 0.2T and not greater than 2 mm are allowed, the weld surface at all other positions shall be at least at the level of the base metal. 6.5 The fillet weld height shall be equal to or greater than 70% of the thickness of the thinner base metal among the two welded pieces, and shall not be less than 3 mm. 6.6 Non-destructive testing methods for welds, proportions, and requirements for drawings regarding acceptance criteria. 7 Quality records: Pipeline welding work record J412, Weld repair report, Non-destructive testing report. 8 Safety considerations: 8.1 Welders’ clothing must meet safety specifications. 8.2 Tools used by welders should be kept in tool bags. 8.3 The erection for working at heights shall comply with safety regulations, and the location shall be suitable for welding operations. 8.4 Electric tool junction boxes shall be equipped with leakage protection devices. 8.5 Safety goggles and a mask should be worn when using a grinder. 8.6 Before using the welding machine, check whether its grounding is proper. 9 The welding processes for aluminum and aluminum alloys are as follows: 1) LF2 welding process: Welding process evaluation code, Applicable plate thickness (mm), Welding method, Wire grade, Wire diameter in mm, Welding current in A, Welding voltage in V, Welding speed in cm/mm, Argon flow rate in L/mm, Welding position. 2-005AWV – MI: 1.5–8 GTAM, LF11, wire diameter φ3; Plate thickness: 100–130 mm; Welding current: 18–20 A; Welding voltage: 5–10 V; Welding speed: 8–12 cm/mm; Argon flow rate: 100–130 L/mm; Welding position: Horizontal fixation. 2-004AWN-MI: 1.5–8 GTAM, LF11, wire diameter φ3; Plate thickness: 100–130 mm; Welding current: 18–20 A; Welding voltage: 5–15 V; Welding speed: 8–12 cm/mm; Argon flow rate: 100–130 L/mm; Welding position: Vertical fixation. 2) SB-209 welding process for 6061 alloy: Welding process evaluation code, Applicable plate thickness, Welding method, Wire grade, Wire diameter in mm, Welding current in A, Welding voltage in V, Welding speed in cm/mm, Argon flow rate in L/mm, Welding position. 2-925GV – MV: 9–18 GMAM, ER5356, wire diameter φ1.2; Plate thickness: 160–180 mm; Welding current: 23–24 A; Welding voltage: 20–30 V; Welding speed: 20–30 cm/mm; Welding position: Horizontal fixation. For tube sheets, plate thickness: 140–160 mm; Welding current: 23–24 A; Welding voltage: 20–30 V; Welding speed: 20–30 cm/mm; Welding position: Vertical fixation