[China Aluminum Network] (1) Aluminum and oxygen have a strong affinity

It is easy to combine with oxygen in the air to form a dense and strong alumina film with a thickness of about 0.1μm and a melting point of up to 2050°C, far exceeding the melting point of aluminum and aluminum alloys, and a density of 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 quality of welding, the surface oxides of the weldment must be strictly cleaned before welding and reoxidation is prevented during the welding process. This effectively protects the molten metal and the metal at high temperatures. This is an important factor in the welding of aluminum and aluminum alloys. Features. The specific protection measures are: using mechanical grinding or chemical method D40 to remove the oxides of the workpiece groove and surrounding parts before welding; use qualified protective gas for protection (such as 99.99% Ar) during welding.

(2) Aluminum has a high thermal conductivity and specific heat

Fast heat conduction Although the melting point of aluminum and aluminum alloys is much lower than that of steel, the thermal conductivity and specific heat capacity of aluminum and aluminum alloys are both large and more than double that of steel. During the welding process, a large amount of heat energy is rapidly transferred to the inside of the collective metal. In order to obtain high-quality welded joints, heat sources with concentrated energy and large power must be used. Preheating and other technical measures must be applied to thick plates of 8 mm or more in order to achieve the fusion welding process.

(3) Large coefficient of linear expansion

The coefficient of linear expansion of aluminum and aluminum alloys is about 2 times that of steel, and the volumetric shrinkage 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, some 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) easy to form pores

Pinholes in welded joints are defects that can easily occur during the welding of aluminum and aluminum alloys, 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. During the cooling and solidification process after welding, the gas will not precipitate, 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 strength and plasticity at high temperatures Low aluminum strength is only 10MPa at 370°C. Welds will not form well because they cannot support liquid metals during welding, and may even collapse or burn through. In order to solve this problem, pads are often used for welding aluminum and aluminum alloys.

(6) No color change, making welding operation 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.

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