With the expansion of the application range of aluminum alloy, more and more problems are highlighted. With the development of research, aluminum alloy welding technology has been greatly developed, at present, the main tungsten argon arc welding (TIG), molten inert gas welding (MIG), laser welding (LBW), friction stir welding (FSW) and so on.

· Argon tungsten arc welding

Tungsten Inert Gas Welding (TIG), a typical inert gas shielded welding, is the most commonly used welding method. During welding, tungsten electrode and welding surface are used as electrodes, and helium or argon is passed between the two poles as a protective gas to protect the arc. The wire and base metal are melted by instantaneous high voltage discharge, and the welding and repair of aluminum alloy parts and casting defects are carried out.

It mainly has the following technical characteristics:

1. Easy to operate, flexible and controllable, suitable for various working conditions, low cost;

2. The heat affected zone is narrow, the deformation of the welded joint is small in the case of sufficient wire feeding, and the comprehensive performance of the joint is higher;

3. Welding process performance is good, stable, the weld formation is dense and beautiful.

· MIG shielded welding

MIG (GMA-Gas Metal Arc Welding) and TIG are both inert gas shielded welding, the difference is that TIG welding uses tungsten electrode as the fixed electrode, while MIG welding uses the filled wire material itself as the electrode.

In the process of MIG welding of aluminum alloy, the voltage and current act on the electrode electrode of the wire and generate instantaneous high pressure between the base metal and the base metal, melt the base metal and the groove, drop off the melt droplet at the end of the wire, and vertically transition to the base metal melt pool to form the welding zone.

However, the application process of aluminum alloy MIG welding is greatly limited, because the soft aluminum wire leads to poor wire feeding, and the molten aluminum is easy to form a phenomenon of "hanging without dropping" during welding, which is easy to cause droplets to splash. Its advantage is that the welding speed of MIG welding is faster than that of TIG welding, the welding motion amplitude is small when welding large workpieces, and the welding efficiency can reach several meters per minute by adjusting the wire feed speed.

· Laser welding

Laser Beam Welding LBW (Laser Beam Welding LBW) uses high-energy laser pulses to locally heat the material in a small area. The energy of laser radiation diffuses to the interior of the material through thermal conduction, and the material is melted to form a specific melt pool. After solidification, the material is connected as a whole.

The advantages of laser welding are that the welding operation point is small, the high-power heat source is concentrated, the ability to perform thick plate welding, the heat affected zone is narrow and the welding deformation is small. However, at the same time, laser welding has higher requirements for welding positioning, expensive welding devices, high welding costs, and high laser reflectivity for metal materials such as aluminum and magnesium, and direct welding is difficult.

Laser irradiation with different power densities shows that when the power density on the workpiece reaches 107W/cm2 or more, the metal in the heating zone will be vaporized in a very short time, and the gas will converge into a small hole in the molten pool, and the heat transfer will be carried out near the small hole, and the molten pool will be formed. This is the "keyhole" effect of laser deep penetration welding. In order to avoid the non-uniform problem caused by this phenomenon, the bubbles in the fusion zone can be removed by reducing the laser energy, increasing the welding speed or controlling the remelting of the core zone.

· Friction stir welding

Friction stir Welding (FSW) is a new solid phase joint technology based on traditional friction welding technology. Its principle is to friction stir welding (FSW), a non-expendable special shape of the head composed of a needle and a shoulder, which will rotate into the interface to be welded. When the friction stir welding head moves along the weld, the temperature of the welding material will increase. The plasticized metal has strong plastic deformation under the action of mechanical stirring and top forging, and forms a dense solid phase connection after diffusion and recrystallization.

Compared with traditional welding methods, FSW technology has the following advantages:

1. Low welding temperature, small welding deformation;

2. Good mechanical properties of weld;

3. The welding process is simple, economic and environmental protection.

The main existing problems and research emphases

With the application of aluminum alloy in more and more industries, the problem of repairing the connection has attracted more and more scholars' attention. Through a variety of welding technology for aluminum alloy welding tests, it is found that the maturity of the repair technology is not up to the needs of industrial development, and there are still various problems.

Argon tungsten arc welding and inert gas welding are the two welding methods that are widely used at present, but the heat affected zone of these two technologies is wide, and the weld metal needs to be melted and recoagulative, which has a great impact on the structure and high residual stress, resulting in serious impact on the mechanical properties of the joint. Laser welding energy beam density is high, weld depth and width is relatively large, but it is very easy to form pores, and its expensive cost also limits the popularity of applications. Friction stir welding provides a solution to the problem of heat, but the friction stir welding requires relatively large forging pressure and forward driving force, and the equipment is generally more complex and heavy, which limits its development.

The research focus of related topics should be placed on the following aspects:

1. Starting from the basis of fusion welding, adjust the formula of welding wire, add rare earth elements or appropriate selection of welding active agents, control the amount of welding deformation, reduce stress, and reduce the formation of pores.

2. Due to the expansion of the scope and use of alloys, they are usually used with heterogeneous materials, so it is necessary to carry out lap fusion welding experiments between dissimilar metals to obtain high-quality joints.

3. Research on weldability of composite heat sources, such as TIG-laser composite welding and laser composite friction stir welding, in order to obtain optimal weld performance.

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