High silicon aluminum alloy welding status

According to the large-scale non-ferrous net finishing: In recent years, domestic and foreign researchers have done a lot of research on high-silicon aluminum alloys in terms of formulation, performance evaluation, etc., but the study of its weldability has been limited to a large extent, limiting the silicon-aluminum alloy. Promotion and application. With the rapid development of science and technology, it is necessary to study and solve the welding problem of high-silicon aluminum alloy. High-silicon aluminum alloy has a wide range of applications in aerospace, aerospace, automotive, space technology and other high-tech fields. It can manufacture heat-pipe components such as microcircuit packages, substrates and cover plates, and wear parts such as pistons and engine cylinders. The key to the development and application of high-silicon aluminum alloys lies in the excellent properties of the alloys. High-silica-aluminum has the advantages of low thermal expansion coefficient, good mechanical properties, and easy precision machining. However, since the affinity of aluminum and oxygen is very strong, it is easily oxidized to form an oxide film that is refractory. The oxide film seriously affects the fusion formation of the weld during the welding of the material. And high silicon aluminum contains a large amount of silicon, easily lead to silicon cracking. Therefore, the high-efficiency and high-quality connection of high-silicon-aluminum is one of the key issues in the field of welding.

High silicon aluminum welding

In the welding process of high-silicon-aluminum, defects such as inclusions, pores and cracks are prone to occur, and how to avoid oxidization to generate slag as much as possible is an important research direction.

Oxidation

Aluminum in high-silica-alumina is easily compatible with oxygen and produces a dense Al2O3 thin film, which is solid and dense. Its melting point is as high as 2050°C, which is far greater than the melting point of high-silicon aluminum alloy. In the welding process, a dense oxide film is formed. It is difficult to remove, seriously affecting the bonding between metals and easily causing slag inclusion. In order to prevent the occurrence of slag inclusion, some measures can be taken. Before the welding, the oxide film on the surface can be removed by mechanical cleaning or chemical cleaning. The mechanical cleaning method is mainly used to clean the oxide film by grinding, boring knife, scraper, and wire brush. The chemical cleaning method can not only clean the oxide film, but also clean the surface of the oil.

Welding porosity

Gases that generate pores include H2/CO/N2. Among them, H is the main source of stomata. The dense oxide film easily absorbs moisture. When soldered, the solubility of hydrogen in liquid aluminum is 0.7 ml/100g. At the solidified state at 660°C, the solubility of hydrogen is 0.04 ml/100g, which makes the hydrogen originally dissolved in liquid aluminum. A large number of precipitation, the formation of air bubbles, and high heat conductivity of silicon aluminum alloy itself is very good, the molten pool crystallization process is very fast, so the gas generated by the metallurgical reaction is too late to escape the surface of the bath, residual pores in the weld. The impure gas and the intrusion of air into the weld zone can also cause internal gas and surface porosity in the weld. Moreover, for the silicon-aluminum alloy prepared by powder metallurgy, the content of the occluded gas is high at the fusion-welding temperature, and pore defects are easily caused. Because the generation of high-silicon-aluminum welding porosity is closely related to the oxide film on the surface of the alloy, it is necessary to prevent the generation of pores. First, the oxide film on the surface of the welding area must be completely removed before welding, and the welding area is easily contaminated before welding. Therefore, care should be taken to prevent contamination before welding, and in particular, the welding face area should be kept clean. To obtain high-quality welded joints, suitable welding methods, specifications and protective measures should also be adopted for welding, and the humidity of the operating environment should be strictly controlled.

Welding crack

In the high-silicon-aluminum welding process, the weld crystallizes and solidifies metal from the liquid metal to the solid metal. The molten pool solidifies and shrinks to generate tensile stress. In the early stage of welding and solidification, the temperature is relatively high, the metal fluidity is good, and the metal liquid can be The free flow between the solidified grains can fill the gap caused by the tensile stress and will not form cracks. In the process of crystallization, the crystal grains that are first crystallized cause the heat affected zone of the welding to crack, but studies have shown that the welding melt The smaller the pool, the less likely it is to crack.

In addition, the silicon content of the high-silicon-aluminum alloy is high, and the heated silicon phase becomes coarser, which has an adverse effect on the toughness and plasticity of the alloy, and is prone to stress deformation and cracking.