WELDING PROCESS 
WELDING PROCESS
CAN ALUMINUM BE WELDED WITH THE MIG/MAG PROCESS?
The answer is very simple: yes, it is possible. In fact, since the early development of the GMAW…
In gas-shielded arc welding processes, the shielding gas has a great influence on both the properties of the deposited metal and the stability of the arc. Therefore, it is necessary that welding be performed in a controlled atmosphere.
In the GMAW process, the controlled atmosphere is achieved by surrounding the arc with a gas, which is supplied through the nozzle. The air in the welding zone is displaced by the flow of the shielding gas. As a result, the arc and the weld pool are maintained within said protective atmosphere; in other words, the purpose of the shielding gas is to prevent the molten metal from coming into contact with air. The surrounding air is composed of 78% Nitrogen, 21% Oxygen, 0.94% Argon, and 0.04% of other gases, mainly Carbon Dioxide, and a certain amount of water in the form of vapor and Hydrogen from moisture in the environment.
Of the gases found in the atmosphere, the most harmful to welding operations are: Hydrogen, Nitrogen, and Oxygen. The consequences of these gases combining with the molten or still incandescent metal are as follows: hydrogen, when dissolved in the electric arc, produces porosity, causing a weakening of the deposited metal; nitrogen, when combined with iron, forms a compound called Iron Nitride, characterized by its great hardness, turning the deposited metal into a brittle metal; oxygen, when combined with iron, forms iron oxides, reducing the mechanical properties of the deposited metal.
Given the harmful effects caused by these three gases, it is essential to eliminate them from the vicinity of the arc or the molten metal during the welding operation. This is achieved through the action of shielding gases, which are divided into two groups: inert and active.
The former are highly stable elements that do not react with other substances; in nature only six inert gases exist: Helium, Neon, Argon, Krypton, Xenon, and Radon, and in welding only Helium and Argon are used, as they are the only ones that can be obtained in reasonable quantities and at reasonable prices.
The latter are basically Carbon Dioxide, and any mixtures containing this gas which, due to their active nature and their reaction with other elements, require the use of wires rich in deoxidizing elements such as, for example, Manganese and Silicon, to compensate for their oxidizing action.
Argon: This gas has been used as a shielding medium in fusion welding for many years; it is obtained by distillation of previously liquefied air.
Pure argon is only used as a shielding gas when welding metals such as Aluminum, Copper, Nickel, and Titanium; when used in the welding of Steels, however, it tends to produce undercuts and beads with very irregular edges.
Helium: Like Argon, it is an inert gas and is obtained through a fractional distillation process of atmospheric air similar to the one applied in obtaining Argon. Its main application is limited to the welding of non-ferrous metals, such as: Aluminum, Copper, and Magnesium.
Carbon Dioxide: The greatest use of Carbon Dioxide as a shielding gas is found in the welding of Carbon Steels. The main characteristic of this gas is that it provides welds with greater penetration, in addition to being much cheaper than Argon and other shielding gases.
Argon + Oxygen Mixture: When welding Carbon Steels and with the objective of improving the bead edges and the penetration profile obtained with pure Argon, mixtures of Argon + Oxygen at 1, 2, or 5% may be used. Oxygen increases penetration, improves the appearance of the joint, and reduces the tendency to form undercuts. Argon + Oxygen mixtures are widely used in the welding of Carbon, Low-Alloy, and Stainless Steels.
Argon + Carbon Dioxide Mixture: When welding Carbon Steels with pure Carbon Dioxide shielding, the best arc characteristics cannot be achieved. This problem tends to arise in joints where good surface appearance must be especially ensured and spatter must be minimized; in this case, Argon + Carbon Dioxide mixtures are used. Argon + Carbon Dioxide mixtures can be used in the welding of Carbon Steels, Low-Alloy Steels, and some types of Stainless Steels.Argon + Helium + Carbon Dioxide Mixtures: The widest field of application for this type of mixture is the welding of Austenitic Stainless Steels, according to AISI, those in the 3XX Series. The use of these mixtures allows for beads with good appearance and very low reinforcement or crown height, which is very important when a smooth surface with minimal reinforcement is desired. For these reasons, it is used in the welding of Stainless Steel piping.
