The author: Release time : 2017-01-04 16:27:42 1240time to browse
(1) strong oxidation ability Aluminum easy to combine with oxygen in air to generate dense solid Al2O3 thin film, the thickness of about 0.1 microns. Al2O3 as high as 2050 ℃, melting point than aluminium and aluminium alloy melting point (660 ℃), and quality of large volume, which is about 1.4 times of aluminum. During the welding process, the alumina film will hinder the good combination between metal, and is easy to form slag. Oxide film will moisture adsorption, prompt production weld porosity when welding. Therefore, must be strictly before welding oxide on the surface of the weld, and strengthen the protection of the welding area.
2 larger thermal conductivity and specific heat capacity of aluminium and aluminium alloy thermal conductivity and specific heat capacity of about 1 times larger than that of steel, the welding process large amounts of heat are rapidly conduction into the base metal. Therefore, the welding of aluminium and aluminium alloy to burn more calories than steel, often take preheating before welding process measures, etc.
(3) hot cracking tendency about 2 times of steel large linear expansion coefficient, freezes the volume shrinkage rate of about 6.5%, so some aluminum alloy welding, tend to produce hot crack due to excessive internal stress. Adjust the wire component method is commonly used in production to prevent thermal cracks, such as using the wire HS311.
(4) easy formation porosity The gas is hydrogen gas hole. Hydrogen solubility in the liquid aluminum is 0.7 mL / 100 g, and in 660 ℃ solidification temperature, the solubility of hydrogen plunged to 0.04 mL / 100 g, which dissolves in the hydrogen in the liquid aluminium, a large amount of precipitation, the formation of air bubbles. At the same time, the density of aluminum and aluminum alloy is small, air bubbles in the molten pool increase slower, and the thermal conductivity of the aluminum is strong, molten pool cooling fast, therefore, the rising bubbles often too late to escape, stay inside weld porosity. Moisture in the atmosphere of arc column, welding material and parent metal surface oxidation film adsorption of water are the main source of hydrogen, so must be strictly before welding to do a good job of weldment surface clean.
5] range joint strength of aluminium and aluminium alloy heat affected zone due to thermal softening, strength reduce the strength of joint and parent metal cannot reach. Pure aluminium and the heat treatment to strengthen the strength of the aluminum alloy joint is about 75% ~ 100% of parent metal; Heat treatment to strengthen the joint strength of aluminum alloy is small, only 40% of the parent metal - 505.
 in aluminium and aluminium alloy welding from solid to liquid, no obvious color change, so the temperature is not easy to judge the parent metal, welding shi often due to the high temperature will be unable to detect and guide to welding.
Aluminium and aluminium alloy what preparation work should be done before welding?
(1) it is the purpose of cleaning cleaning before welding to remove oxide film on the surface of the weldment and the oil, it is one of the important measures to prevent produce blowhole, slag.
A chemical cleaning cleaning up, stable quality, high efficiency welding wire and welding parts size is not big, batch production. Chemical cleaning points immersion method and scrubbing method two kinds, cleaning agents and cleaning technology, see table.
Aluminium and aluminium alloy chemical cleaning method
B mechanical cleaning With organic solvent (acetone, rosin or gasoline) wipe the oil on the surface of the weld, then with fine copper wire brush to the surface above metallic luster, or with surface of scraper to clean up. Clean up after the welding should be within 4 h welding, otherwise should clean up again.
2 plate In order to ensure the weld penetration and welding without welding, wear, or collapse under the joint plate was laid before welding. Can use graphite plate material, stainless steel or carbon steel, open a circular arc wall surface, to ensure that the reverse side of weld.
(3) preheating welding of thin, small, can generally without preheating. When the welding of weldment thickness more than 5 mm, in order to make the seam near to reach the required temperature, should butt welding pieces of preheating before welding, preheating temperature is 100 ~ 300 ℃.
Aluminium and aluminium alloy welding shall be carried out after the cleanup?
And adjacent parts after welding in welding residual flux and welding slag, need to clean up in time, or in the air, water, under the action of residual solvents and slag can destroy have antiseptic effect of alumina film, hot corrosion weldment. Therefore, should immediately after welding strictly to remove residual dirt on weldment.
The commonly used slag removal methods and steps:
1) in hot water with a hard brush carefully wash welded joint.
2) the weldment in the temperature of 60 ~ 80 ℃, the mass fraction of 2% ~ 3% of chromic anhydride in aqueous solution or potassium dichromate solution soaking for about 5 ~ 10 min, and scrub brush carefully cleaning. Or put in 15 ~ 20 ℃ the weldment in the mass fraction of 10% nitric acid solution immersion 10 ~ 20 min.
3) in hot water washing away weldment.
4) weldment with blowing hot air dry, or within 100 ℃ drying oven drying.
Test of aluminium and aluminium alloy tungsten argon arc welding, the welding process.
(1) the selection of welding wire aluminum and aluminum alloy welding wire brands are shown in table 2. Including HS311 is a kind of universal wire, using this kind of welding wire welding, metal liquidity is good, have higher thermal cracking performance, and can guarantee a certain strength. But when welding aluminum magnesium alloy, there will be a brittle compounds in weld Mg2Si, reduce plastic and corrosion resistance of joint. When the welding aluminium magnesium alloy HS331 should be adopted.
Aluminum and aluminum alloy welding wire
2 weld and groove form Groove form shown in table 3.
(3) welding power source should be chosen ac power.
70 test of aluminium and aluminium alloy tungsten argon arc welding, the welding process parameters.
Aluminium and aluminium alloy the manual tungsten argon arc welding and automatic tungsten argon arc welding welding process parameters, see table 4, 5, respectively.
Aluminium and aluminium alloy manual tungsten argon arc welding welding process parameters
Aluminium and aluminium alloy tungsten argon arc welding welding process parameters automatically
Test of aluminium and aluminium alloy melting pole argon arc welding, the welding process parameters.
Automatic and semi-automatic melting pole argon arc welding of aluminium and aluminium alloy welding process parameters, respectively, as shown in table 6. Welding power source USES the dc reverse connection.
Aluminium and aluminium alloy melting pole argon arc welding welding process parameters automatically
Test of aluminium and aluminium alloy, the gas welding process.
(1) the form aluminum and aluminum alloy welding joint, unfavorable use lap joints and T joint, because these joint easy to residual gas welding flux and welding slag, inconvenient to clean up after welding.
2 flame and welding nozzle number When welding flame can use neutral flame (or mild carbonizing flame), undertake choosing according to the thickness of the aluminum plate welding nozzle number, are shown in table 7.
(3) positioning welding welding process parameters are shown in table 8.
(4) welding nozzle Angle and wire Thin plate welding, welding nozzle Angle is about 30 ° to 45 °, wire Angle of about 40 ° ~ 50 °; Thick plate welding, the welding nozzle Angle should be about 50 °, wire Angle of 40 ° ~ 50 °.
Aluminium and aluminium alloy welding welding process parameters
Aluminium and aluminium alloy welding position welding process parameters
The next article：In the wave soldering flux principle