TIG Welding Anodized Aluminum – The Fundamentals

When you mention TIG welding anodized aluminum, one is reminded of poking a into a thin sheet of ice, leaving the water beneath undisturbed. Here, the solid sheet of oxide which is formed due to anodization procedure can be compared to the ice and the pulpy aluminum beneath is the water.

Anodized aluminum is nothing but the basic aluminum which has been processed to create a thick sheet of oxides on its exterior. The base aluminum is a very soft and pulpy material which melts at about 1100áµ’ F, though the sheet of oxide is exceptionally hard (in some cases it can be as hard as diamonds) and melts at around 3600áµ’ F. The problem to weld anodized aluminum depends on the removal of the sheet of oxide avoiding to burn through the base of the aluminum.

It is interesting that these elements of the layer of oxide are what are responsible for making the anodized aluminum into a useful material. Since it is comparatively cheap, appealing to the eye, exceedingly averse to corrosion, extremely lightweight – especially in environments of high salinity - anodized aluminum is a usual material in the coastal areas. It is effectively utilized for rod holders, tuna towers, wakeboard towers, bow rails, t-tops and chairs on the sport fishing boats, etc.

Even in the absence of any kind of treatment, aluminum innately creates an extremely thin sheet of oxides. An electrolytic chemical procedure, normally with Sulfuric acid is used in the procedure to anodize aluminum to generate a sheet of oxides many times more denser that it would form naturally – which ranges between .0002 and .001 inch in thickness.

The standard, bright finish, colored and hardened is the four types of anodized aluminum.

The bright finish type of anodized aluminum is visually notable from the anodized aluminum because of its shiny and its finish which is chrome-like. This kind of substance includes a thicker sheet of oxides than the standard anodized aluminum, making GTAW welding more difficult and is utilized basically for cosmetic causes.

Colored anodized aluminum is again utilized for cosmetic reasons. This substance makes use of dyes the process of anodization, and makes it possible for the substance to accept various hues and also to initiate potential pollutants into the weld.

The hardened anodized aluminum which is nearly as solid as diamond is very tough to weld. This kind of substance is normally utilized in extremely specialized industrial operations which are not going to be discussed here in detail.

Though all, the standard, colored and bright finish anodized aluminum make use of more or less similar preparation, technique and equipment as standard aluminum, to be welded triumphantly, some need some distinctive considerations.

Choice of Equipment

In order to have a successful weld, the first step is the choice of the right equipment. Substances distinctive to anodized aluminum comprise a 5356 class filler metal and a torch having a fingertip control. A torch that is air-cooled is acceptable in order to weld below 200 amps though a torch that is water-cooled is required for procedures which need more amperage.

Anodized aluminum, just like standard aluminum requires a 100 percent Argon/Helium mixture or Argon shielding gas along with a 2 percent Thoriated or Ceriated tungsten. [Note: Since Thorium is radioactive, care should always be taken to comply with the manufacturer’s instructions, warnings and the MSDS (Material Safety Data Sheet) before using it.] You can use pure tungsten (green stripe) though only to about 70 percent amperage of Thoriated or Ceriated tungsten.

For preparing the tungsten, you will have to grind it to the very same kind of level used for stainless steel or steel. Regrinding of the tip is required as it slowly rounds off and while the arc gets unstable, continuing the procedure as needed. A source of current competent of alternating current (AC) is also required since it is the electrode positive part of the current cycle that causes the splitting away of the layer of oxide.

Though the traditional and transformer supported TIG current sources can successfully be utilized for the welding of anodized aluminum, for both its frequency control and balance, it is strongly recommended that an inverter is made use of.

The balance controls permits the user to determine the period of time that the current stays in each point of the AC cycle. For instance, a balance control that is adjusted to 30/70 would mean that the currents stays 30 percent of its cycle as electrode positive, clearing the oxide layer away from the base substance and 70 percent on electrode negative, directing the electrical power into the joint of the weld thereby joining both the pieces of substance. The real balance control adjusting will be decided by the skill and experience of the welder. A more skilled and experienced operator would opt to use a higher percentage of electrode negative (between 80 and 90 percent) so as to work faster.

The advantage of using an inverter is that the frequency control function available there will permit the operator to decide the period of time for the unit to make a complete round of current cycle (the combined time that is spent on both the electrode negative and electrode positive.)

The transformer supported sources of power is only capable of producing an output of 60Hz (in Canada it is 50Hz), which is similar to the frequency to that coming from the wall powered containers. Inverters, on the other hand, are capable of adapting to any frequency from as less as 20Hz to as high as 400Hz. Anodized aluminum at a frequency between 160 to 200Hz usually brings about the greatest outcomes. The heightened frequency generates a narrower cone of arc and as a result, a heated affected zone and a narrower weld bead. The weld’s strength increases because the field of the base substance exposed to the arc’s heat is reduced. A narrower weld bead brings down the filler material and the time required creating the weld.

A backhanding technique is also eliminated while using an inverter. Backhanding – also referred to as backing around the weld, entails forming two passes on each of the joints in the welds – one of the passes going ahead to wipe off the layer of oxide and later reversing the route to add filler metal to the region that was just cleaned. Besides doubling the period taken to weld the joint, it can also decrease the weld’s strength since backhanding demands that the work piece be heated twice.