The hottest test on the weldability of aluminum an

2022-08-16
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Try to describe the weldability of aluminum and aluminum alloys

try to describe the weldability of aluminum and aluminum alloys

⑴ strong oxidation ability aluminum is very easy to combine with oxygen in the air to form a dense and solid Al2O3 film, with a thickness of about 0.1 μ m。 The melting point of Al2O3 is as high as 2050 ℃, which is much higher than that of aluminum and aluminum alloys (about 660 ℃), and its volume and mass are large, about 1.4 times that of aluminum. During the welding process, alumina film will hinder the good bonding between metals, and it is easy to form and should not be used as slag inclusion. The oxide film will also absorb water, which will promote the formation of pores in the weld during welding. Therefore, the oxide on the surface of the weldment must be strictly cleaned before welding, and the protection of the welding area must be strengthened

⑵ large thermal conductivity and specific heat capacity. The thermal conductivity and specific heat capacity of aluminum and aluminum alloy are about twice that of steel. A large amount of heat is rapidly transmitted to the base metal during welding. Therefore, welding aluminum and aluminum alloys consumes more heat than steel, and preheating and other technological measures are often required before welding

⑶ hot cracks tend to be large, the linear expansion coefficient is about twice that of steel, and the volume shrinkage during solidification is about 6.5%. Therefore, when welding some aluminum alloys, hot cracks often occur due to excessive internal stress. In production, the method of adjusting the composition of welding wire is often used to prevent thermal cracks, such as using welding wire hs311

⑷ the gas that is easy to form pores is hydrogen. The solubility of hydrogen in liquid aluminum is 0.7ml/100g, while at the solidification temperature of 660 ℃, the solubility of hydrogen suddenly drops to 0.04ml/100g, which makes a large amount of hydrogen dissolved in liquid aluminum precipitate and form bubbles. At the same time, the density of aluminum and aluminum alloy is small, and the rising speed of bubbles in the molten pool is slow. In addition, aluminum has strong thermal conductivity and rapid condensation in the molten pool. Therefore, the rising bubbles often do not have time to escape and remain in the weld to become pores. The water in the arc column atmosphere and the water absorbed by the oxide film on the surface of welding materials and base metals are all the main sources of hydrogen, so the surface cleaning of weldments must be strictly done before welding

⑷ the heat affected zone of aluminum and aluminum alloy with unequal strength of the joint softens and the strength decreases due to heating, so that the joint and the base metal cannot reach the same strength. The strength of pure aluminum and non heat treatment strengthened aluminum alloy joints is about 75% - 100% of the base metal; The joint strength of heat-treated strengthened aluminum alloy is small, only 40% - 505 of the base metal

⑥ when welding through aluminum and aluminum alloy from solid to liquid, there is no obvious color change, so it is difficult to judge the base metal temperature, and welding will often lead to welding through because the temperature is too high to be detected

what preparations should be made before aluminum and aluminum alloy welding

⑴ the purpose of pre welding cleaning is to remove the oxide film and oil stain on the surface of the weldment, which is an important measure to prevent pores and slag inclusions

a chemical cleaning has high efficiency and stable quality. It is suitable for cleaning welding wires and weldments with small size and mass production. Chemical cleaning can be divided into immersion method and scrubbing method. See the table for cleaning agent and cleaning process. Chemical cleaning of aluminum and aluminum alloys

b mechanical cleaning first wipe the oil stain on the surface of the weldment with organic solvent (acetone, rosin or gasoline), and then brush it with thin copper wire until the surface shows metallic luster, or clean the surface with a scraper. The cleaned weldment shall be welded within 4h, otherwise it shall be cleaned again

⑵ backing plate in order to ensure full penetration and prevent welding penetration or collapse of weldments, backing plates can be placed under the joints before welding. The backing plate material can be graphite, stainless steel or carbon steel, with an arc-shaped groove on the surface to ensure the formation of the reverse weld

⑶ preheating is generally unnecessary for thin and small weldments. When welding weldments with a thickness of more than 5mm, in order to reach the required temperature near the joint, the weldments should be preheated before welding. The preheating temperature is 100 and the anti-interference ability is poor ~ 300 ℃

what cleaning work should be done after aluminum and aluminum alloy welding

the residual flux and welding slag left in the weld and adjacent after welding of the weldment need to be cleaned in time, otherwise under the action of air and moisture, the residual solvent and welding slag will damage the aluminum oxide film with anti-corrosion effect and severely corrode the weldment. Therefore, the residual dirt on the weldment should be strictly removed immediately after welding

common slag removal methods and steps:

1) carefully wash the welded joints with a hard brush in the main interface after the hot water system self-test and automatic valve port reset

2) soak the weldment in chromic anhydride aqueous solution or potassium dichromate solution with a temperature of 60 ~ 80 ℃ and a mass fraction of 2 ~ 3% for about 5 ~ 10min, and carefully wash it with a hard brush. Or immerse the weldment in 10% nitric acid solution at 15 ~ 20 ℃ for 10 ~ 20min

3) wash the weldment in hot water

4) dry the weldment with hot air or dry it in a 100 ℃ drying oven

try to describe the welding process of tungsten argon arc welding of aluminum and aluminum alloy

⑴ the selection of welding wire. See Table 2 for the brand of welding wire for aluminum and aluminum alloy. Among them, hs311 is a general-purpose welding wire. When using this kind of welding wire, the metal has good fluidity, high heat crack resistance, and can ensure a certain strength. However, when welding aluminum magnesium alloy, brittle compound Mg2Si will appear in the weld, which will reduce the plasticity and corrosion resistance of the joint. Hs331 shall be used when welding aluminum magnesium alloy. Welding wire grades for aluminum and aluminum alloys

⑵ welding joints and groove forms. See Table 3 for groove forms

⑶ the welding power supply should be AC power supply

70 describe the welding process parameters of tungsten argon arc welding of aluminum and aluminum alloys

see Table 4 and table 5 for welding process parameters of manual TIG welding and automatic TIG welding of aluminum and aluminum alloy respectively. Aluminum and aluminum alloy manual TIG welding process parameters

aluminum and aluminum alloy automatic TIG welding process parameters

try to describe the welding process parameters of aluminum and aluminum alloy MIG welding

see Table 6 for welding process parameters of automatic and semi-automatic consumable electrode argon arc welding aluminum when using steel wire hook to pull out the steel ball of oil pump outlet valve and aluminum alloy. The welding power supply adopts DC reverse connection. Welding process parameters of automatic consumable electrode argon arc welding of aluminum and aluminum alloys

try to describe the gas welding process of aluminum and aluminum alloys

⑴ joint form lap joints and T-joints should not be used in gas welding of aluminum and aluminum alloys, because these joints are prone to residual gas welding flux and welding slag, which is inconvenient to be cleaned after welding

⑵ flame and nozzle number during gas welding, neutral flame (or slight carbonization flame) can be used. The nozzle number is selected according to the thickness of aluminum plate, as shown in Table 7

⑶ see Table 8 for the process parameters of tack welding

⑷ inclination of welding nozzle and welding wire when welding thin plates, the inclination of welding nozzle is about 30 ° ~ 45 °, and the inclination of welding wire is about 40 ° ~ 50 °; When welding thick plates, the inclination of welding nozzle should be about 50 °, and the inclination of welding wire should be 40 ° ~ 50 °. Aluminum and aluminum alloy gas welding process parameters

aluminum and aluminum alloy gas welding positioning welding process parameters

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