There are many methods used for aluminum alloy welding, mainly tungsten gas shielded welding and consumable gas shielded welding. In addition, methods such as tungsten pulse argon arc welding, consumable pulse argon arc welding, plasma arc welding, tungsten direct current helium arc welding, and vacuum electron beam welding are also commonly used.

An important feature of aluminum and aluminum alloy welding is that its electrodes, arcs, welding pools, and metals at high temperatures should be in a protective gas.

 Why do we need protective gas?

On the one hand, it is necessary to explore the characteristics of aluminum, as in conventional air, it is easily combined with oxidation to form a stable alumina film, with a melting point of up to 2050 ℃. Moreover, the alumina film has strong adsorption properties, and the adsorbed water can promote the formation of pores in the weld seam during welding. In arc welding, if the oxide film needs to be removed, it is achieved through the impact effect of ionized protective gas and the electronic fragmentation effect from the workpiece to the electrode, which is relatively complex.

Compared to steel, aluminum has different physical, chemical, and mechanical properties, resulting in its completely different welding characteristics from steel. For example, aluminum has a significantly low melting point (560-660 ℃), but due to its high thermal conductivity and melting heat, the heat required for aluminum welding is equivalent to that of steel.

When aluminum cools and solidifies, it produces significant shrinkage and a large coefficient of thermal expansion, which can cause shape changes during heating and cooling processes, easily leading to welding cracks, deformation, and residual stress.

In addition, argon or helium gas should be selected, as inert gases have a persistent neutrality in chemistry and do not form compounds with molten metal or oxygen in the air at high temperatures. Therefore, using inert gas as a shielding gas in arc welding of aluminum alloys, such as the C02 active gas used in welding steel, is not suitable for welding aluminum and aluminum alloys.

Normally, pure argon gas protection is used for aluminum alloy welding. There are also mixtures of argon and helium, and of course, there are also those that use pure helium.

So, what are the requirements for selecting shielding gas argon or helium for aluminum alloy welding?

Firstly, the purity of argon or helium gas used must be greater than 99.99%, and its dew point should be lower than -50 ℃ (when the pressure is 1 bar). For example, the 99.999% purity of Bao Sude liquid argon can meet on-site needs.

The function of argon or helium gas is to prevent air from entering the molten pool, providing effective protection for molten metals and metals at high temperatures. Inert shielding gas can also play a role in stabilizing the arc.

Secondly, under the same welding current, the arc power and heat concentration of helium gas are higher than that of argon gas. However, argon can generate a more obvious and stable arc, and using argon is easier to ignite the arc than helium. Therefore, for AC tungsten gas shielded welding, argon or argon helium mixture is preferred as the shielding gas.

Aluminum alloy welding, using argon and helium gas, a mixture of single or two gases, has been reliably applied in production practice. The basic difference between argon and helium lies in their atomic weights and differences in arc voltage. It should also be noted that due to the lower density of helium compared to argon, a helium flow rate of 2.5 to 3 times is required to achieve the same protective effect as argon.