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Aluminum: Minimize Hydrogen for X-Ray-Quality Welds

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Thursday, November 2, 2017
 


Photo courtesy of Jenny Ogborn, Lincoln Electric
Hydrogen is the most abundant element in the universe, so trying to completely escape its presence is difficult, if not impossible. But minimizing the effects of hydrogen is critical to achieving the highest caliber weld on aluminum, one of X-ray quality.

Following the proper steps will result in clean base metal and wire, proper gas coverage and the appropriate welding technique to sustain gas coverage, whether welding with the gas-metal arc (GMAW) or gas-tungsten-arc (GTAW) process.

A quality weld depends on a number of factors; here we will concentrate on steps to avoid porosity.

Clean, Don’t Just Brush

The metallurgical properties of aluminum are such that it absorbs nothing from the atmosphere—including hydrogen—in its solid state. However, the metal’s ability to absorb hydrogen substantially increases as it heats up.

The source of hydrogen in the atmosphere is humidity (H2O), which can exist on both the base metal and wire. On the base metal, the presence of oil, grease, water and other contaminants can result in hydrogen buildup. The metal should be degreased using a substance such as acetone, nonchlorinated brake cleaner or citrus cleaner.

While aluminum can be brushed to reduce the oxide layer, which absorbs hydrogen, it’s important to remember that brushing is not synonymous with cleaning. Brushing will smear contaminants over a larger area of the material.

A high-quality, clean consumable is a must. It should be properly stored before and after use to keep it contaminant-free. As with the base metal, an oxide-layer buildup on the consumable will contain hydrogen. Also important to note, to achieve X-ray-quality welds on aluminum, the filler metal, too, should be aluminum.

Gas Shielding Keeps Humidity at Bay

The laptop shows an x-ray of an aluminum weld. Key to obtaining welds that pass the x-ray test is minimizing the effects of hydrogen. Fortunately, steps such as proper cleaning, use of proper shielding gases, and minding weld angle and speed can be taken to do just that. Photo courtesy of Jenny Ogborn, Lincoln Electric.
In most cases, the shielding gas will be 100-percent argon. Some heavy aluminum materials may necessitate an argon-helium blend, as the helium adds heat to the puddle. The gas shielding will help prevent humidity from getting inside the weld.

Angles, Speed Are Critical

Angles are important when trying to achieve X-ray-quality welds. The work angle, or angle to the workpiece, should be 45 deg., and the travel angle should be 10-20 deg. The objective is to maintain gas coverage. Coverage will be lost if the work and travel angles are off, leading to porosity. The correct angles maximize the level of gas coverage to ensure that nothing from the atmosphere gets into the weld puddle. In addition, the push, rather than the drag, technique is required because the shielding gas must purge the area ahead of the weld.

Travel speed is critical as well. Go too quickly and the weld will be colder with little or no penetration. Go too slowly and the weld will ball up. In both cases, a lack of fusion will occur.

An X-ray-quality weld is a superior weld, widely considered to be the gold standard in skill. Achieving such a quality weld takes time and experience. Do-overs will be common, especially early on, so don’t be afraid to continually practice the technique on coupons. FPN

Article provided by Lincoln Electric Co., Cleveland, OH; 888/935-3878, www.lincolnelectric.com.

 

As seen in Fabricating Product News: Lincoln Electric Co.