[China Aluminum Industry Network] (1) Aluminum alloys have strong affinity with oxygen and can easily combine with oxygen in the air to form a dense and strong alumina film with a thickness of about 0.1 μm and a melting point of up to 2050°C, far exceeding that of aluminum and aluminum. The melting point of aluminum alloy, and the density is very large, about 1.4 times that of aluminum. During the welding process, the aluminum oxide film can prevent good bonding between the metals and can easily cause slag inclusion. Oxide film also adsorbs moisture, which causes the weld to form pores during welding. These defects will reduce the performance of welded joints. In order to ensure the welding quality, the surface of the weldment must be strictly cleaned of oxides before welding, and to prevent reoxidation during the welding process, to effectively protect the molten metal and the metal at high temperatures, which is an important welding of aluminum and aluminum alloys Features. The specific protective measures are: using mechanical grinding or chemical method D40 to remove the oxide of the workpiece groove and surrounding parts before welding; use qualified protective gas for protection (such as 99.99% Ar) during welding.
(2) Thermal conductivity and specific heat of aluminum alloy Aluminum and aluminum alloys have large thermal conductivity and specific heat capacity. During the welding process, a large amount of thermal energy is quickly transferred to the inside of the collective metal. In order to obtain high-quality welded joints, it must be adopted. For heat sources with concentrated energy and large power, 8mm and above thick plates need to adopt preheating and other technological measures to achieve the fusion welding process.
(3) Linear expansion coefficient of aluminum alloy body The coefficient of linear expansion of large aluminum and aluminum alloys is about 2 times that of steel, and the volume shrinkage rate when solidified reaches 6.5% to 6.6%, so that it is easy to produce welding distortion. An effective measure to prevent deformation is to use a suitable welding tool besides choosing a reasonable process parameter and welding sequence. This is especially true when welding thin plates. In addition, certain aluminum and aluminum alloys have a tendency to form crystal cracks in the weld metal and a tendency to form liquefied cracks in the heat-affected zone when they are welded, often within the brittle temperature range due to excessive internal stress. Thermal cracking is one of the more common serious defects in aluminum alloys, especially high-strength aluminum alloys. The measures to prevent such cracks in the actual welding site are mainly to improve joint design, select reasonable welding process parameters and welding sequence, and adopt welding filler materials that are suitable for the characteristics of the parent material.
(4) Holes in the welded joints of aluminum alloy parts are easily formed. The pores in the welded joints are easily generated when aluminum and aluminum alloys are welded, especially the welding of pure aluminum and rust-proof aluminum. Hydrogen is the main reason for the generation of pores in the welding of aluminum and aluminum alloys, which has been proved by practice. The source of hydrogen is mainly moisture in the arc column atmosphere, the welding material and the moisture absorbed by the parent material. The moisture absorbed by the oxide film on the surface of the welding wire and the parent material often occupies a prominent position in the generation of pores in the weld. Aluminum and aluminum alloy liquid pools can easily absorb pores. A large amount of gas dissolved at high temperatures will rapidly decrease in solubility when solidified from the liquid phase. The gas will not precipitate in the process of cooling and solidification after welding, but will accumulate in the weld. Stoma. In order to prevent the generation of blowholes and to obtain good welded joints, the source of hydrogen must be strictly controlled. Before welding, the moisture content of the used welding materials (including welding wire, welding rod, flux, and shielding gas) must be strictly limited. Strictly carry out drying treatment. The cleaned base metal and welding wire are preferably welded within 2 to 3 hours, and more than 24 hours. During TIG welding, a large welding current is selected to match the higher welding speed. When MIG welding, use a large welding current slow welding speed to increase the existence of the molten pool.
(5) Aluminum alloy strength and plasticity at high temperature Low aluminum strength is only 10MPa at 370°C. When the welding is performed, the weld seam may be poorly formed due to failure to support the liquid metal, and even collapse or burn-through may occur. In order to solve this problem, pads are often used for welding aluminum and aluminum alloys.
(6) Aluminum and aluminum alloys have no color change during welding, making welding operations difficult.
When the aluminum and aluminum alloys are changed from a solid state to a liquid state during welding, there is no noticeable color change, and therefore, the operator has many difficulties in the welding process. Therefore, the welder is required to have a good grasp of the heating temperature during welding, and to use flat welding as much as possible to induce (accept) the arc on the lead (receiving) arc plate.
1.Welding characteristics: Aluminum and aluminum alloys have characteristics of high thermal conductivity, large heat capacity, large linear expansion coefficient, low melting point and low high temperature strength, etc. It is difficult to weld, and certain measures should be taken to ensure the welding quality.
2. Cleaning of pipe fittings and welding wire. Clean the surface of the wire within 50mm of both sides of the wire and breakage with acetone. Brush the surface oxide film with a stainless steel wire brush to expose the metal luster. The clean break must be welded within 2 hours. A good wire is placed in an unused cartridge and must be used within 8 hours or it will be reprocessed.
3. Tungsten rods are made of tantalum-tungsten rods, and the argon blunt quality is not less than 99.96%, and the water content should not exceed 50 mg/m3.
4. The ambient temperature is not lower than 5 °C, otherwise it should be preheated to 100 ~ 200 °C before welding, relative humidity control.
Aluminum alloy body welding technical characteristics and welding precautions