Welding aluminum is much different than welding steel due to their differences in chemical composition. Either the TIG or MIG method should be used when welding aluminum.
- Welding aluminum is done using two preferred methods, both of which employ inert gases, pure argon, or a mix of argon with helium.
- Argon is about ten times the cost of carbon dioxide, commonly used to weld carbon steel.
- Welds often absorbed hydrogen gas and trapped oxide inclusions. If the flux used wasn't thoroughly neutralized with sulfuric acid, corrosion occurred around the welds. The acid cleaner presented a hazard to the welder's lungs and his clothing. Such welds were satisfactory, but they wouldn't qualify for applications where your life depended on them.
- Today, TIG and MIG welding are the two recommended options for welding aluminum. TIG means Tungsten Inert Gas, a shorter acronym for Gas Tungsten Arc Welding (GTAW). The process uses a hand torch with a non-consumable tungsten or tungsten alloy electrode to strike an arc.
- High frequency alternating current, the preferred electrical source for manual welding is controlled by either a torch trigger or foot controlled rheostat. An alternating current gives the arc a cleaning action and divides the heat evenly between the tungsten electrode and the weld pool. TIG is slower than MIG welding, but it allows for more welder manipulation without the fixtures for faster automated production.
- MIG welding, an acronym for Gas Metal Arc Welding (GMAW), uses a consumable electrode, aluminum alloy wire fed through the torch along with the inert gas. Unlike TIG welding, MIG occupies one hand.
- Aluminum has characteristics that make welding its alloys different than welding steel, which is the reason many fabricators "job-out" their aluminum work to fabricators specializing in the process. One-third the weight of steel, aluminum thermal conductivity is six times greater. The rapid heat transfer makes the weld solidify faster than steel. Steel melts at 2,800 degrees Fahrenheit, while pure aluminum melts at 1,220 degrees Fahrenheit. However, surface oxides, one of aluminum's natural barriers against corrosion, melt at much higher temperatures, around 3,725 degrees
- Aluminum oxide abrasives are common grit materials in most shops because aluminum oxide is one of the hardest substances known, second only to diamonds. These same oxides are heavier than aluminum, and their presence destroys expensive milling cutters if the oxides are trapped in welds where finish machining has been done. Gas entrapment occurs with tell tale porosity in the welds.
- Dozens of aluminum alloys can be obtained in wrought forms such as rolled bar stock, sheet, plate, extrusions, and pipe. Some aluminum alloys respond to heat treatment. The nomenclature for both cast and wrought alloyed aluminum Cast grades of aluminum can be easily distinguished by their three-digit numbers like 206, 319. 356. The next time you stop at a red light look at the base of the traffic light and its support column. That's a common aluminum fabrication, a cast base welded to a tapered aluminum pipe.
- Cast grades of aluminum, because of their higher silicon content for fluidity, do not anodize as well as wrought alloys. The two are difficult to color match, and the same is true of aluminum filler rods and the base alloy. The common filler rod for welding heat-treatable alloys like the 6XXX series is 4,043. When black anodizing a
- According to statistics followed by the Aluminum Association, there has been an increase of 26 percent (13,197 to 16,664 million pounds) in usage of wrought.
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