Tungsten Inert Gas Welding [TIG]
The welding of aluminium, magnesium alloys and stainless steels by the Oxy-Acetylene and MMA processes require the addition of a corrosive flux, however this is overcome in the Tungsten Inert Gas [TIG] process by the use of an inert [dead] gas Argon.
The choice of current is based around the principle of DC for ferrous alloys as well as copper and its alloys, AC for aluminium and its alloys. [also aluminium bronze]
The arc burns between a tungsten electrode [Thoriated for DC and Zironiated for AC] and the work piece within the shield of inert gas, argon, which excludes the atmosphere and prevents contamination of the tungsten electrode and 
the molten pool. The hot tungsten arc ionizes the arc gap, between tungsten and work piece, allowing the filler rod to melt, at the same time forming a molten pool in the base material. It is essential that the molten tip of the filler rod is kept within the inert gas shield to avoid any contamination.
Which TIG Rod?
TIG Welding rods are selected based on their compatibility with the base materials and the more common ones are listed below:-
- A] Mild & Low Alloy Steels
- B] Stainless Steels
- C] Cast Iron
- D] Wear facing [Hard facing]
- E] Aluminium
- F] Bronzes
- G] Copper
A] Mild and Low Alloys Steels
BS:2901 A15
AWS ER 70S-2
A triple deoxidised copper coated mild steel alloy containing manganese and silicon, for joints in mild and low carbon steel sheet, rod, or bar.
BS:2901 A18
AWS ER 70S-6
A deoxidised rod for joints in mild steel
B] Stainless Steels
BS:2901 308S92
EN ISO 14343: 19 9 L
For the welding of stainless steels of the 18/8 type. This alloy has maximum carbon content of 0.03% which increases the resistance to inter-granular corrosion.
BS:2901 316S92
EN ISO 14343: 19 1 3 L
Suitable for the welding of austenitic acid resisting steels, particular resistance to pitting corrosion.
BS:2901 309S92
EN ISO 14343: 23 12 L
For the welding of corrosion and heat resistant stainless steels. The low carbon content [0.03% maximum] increases resistance to inter-granular corrosion. 309L superior to 309 for the cladding of carbon or low alloy steels as well as for dissimilar joints that require heat treatment.
BS:2901 310S92
EN ISO 14343: 25.20. L
For joint in stainless, heat resistant and cast steels. Sutable for cryogenic applications and stainless chromium irons.
C] Cast Iron
High nickel content alloy for machineable overlays and joints in most weldable grades of cast iron. Ideal for casting reclamation and machining error rectification.
D] Wear facing [Hard facing]
HF6 alloy for reclamation of machining errors in tool and die steels. Also suitable for overlaying of steel to obtain a wear resistant finish.
E] Aluminium
BS:2901 1050A [GIB]
EN ISO 18273 S Al 1070
For the welding of pure aluminium sheet and extrusions and the end product requires anodising.
BS:2901 4043A [NG21]
EN ISO 18273 S Al 4043A
An aluminium 5% silicon alloy. Suitable to for the welding of cast and wrought aluminium alloys in the range H9[6063], H20[6061] & H30[6082].
This alloy should not be used if the end product requires anodising.
BS:2901 4047A [NG2]
EN ISO 18273 S Al 4047A
A 12% silicon aluminium alloy. Free flow alloy for joints and machining error reclamation in silicon bearing aluminium alloys. Do not use this alloy if the end product requires anodising as discolouring of the welded joint will occur.
BS:2901 5356 [NG6]
EN ISO 18273 S Al 5356
A 5% magnesium containing aluminium alloy. Suitable for high strength joints in most weldable aluminium alloys. This alloy can also be used where the end product requires anodising.
F] Bronzes
BS:2901 C11
EN 14640 Cu 5180
A 7% tin phosphor bronze alloy, for joints in phosphor bronze castings and brasses/bronzes.
BS:2901 C13
EN 14640 Cu 6180
A 10% aluminium, copper based alloy for overlaying and joints in aluminium bronzes. Also for joining these to steel and copper alloys. This alloy can also be used as a corrosion and sliding surface wear resistant [low coefficient of friction] deposit.
BS:2901 C20/26
EN 14640 Cu 6328
A manganese, nickel, aluminium bearing copper alloy for joining and rebuilding castings and components of similar composition. Suitable for marine grade aluminium bronzes
G] Copper
BS:1453 C1
EN: 14640 Cu 1897
A free flowing copper rod for use on application within the food, drink and electrical industries. Suitable for the welding of copper vessels, tanks etc.