Two hundred years on and aluminum is still going strong. Aluminum has come a long way since it was first produced in 1824. It is a pervasive mainstay in the consumer goods, machinery and equipment sectors as well as in the electrical industry and many more.
Today, construction and transportation sectors account for a hefty 52 percent of global aluminum consumption with automotive and aerospace applications driving the metal’s growth as never before. In North America, demand for aluminum appears to be insatiable.
In 2016, the latest year for which statistics are available, demand for aluminum had hit a seventh straight year of growth, according to the U.S. Aluminum Association. Within that seven-year period, aluminum demand grew by an impressive 41 percent. Worldwide, aluminum consumption is second only to steel. Since 2000, global aluminum consumption has exceeded production roughly every other year.
But what are the implications for metalworkers who work with aluminum? As with steel, metalworkers can be faced with challenges when working with aluminum. However, there are plenty of shop floor challenges unique to the lightweight metal.
Strengths and weaknesses
As with all materials, the “metal with wings” has several advantages that are desirable in a variety of applications. Aluminum’s high strength-to-weight ratio has long made it an obvious choice in automotive and aerospace sectors because of its lightweight properties and fuel efficiency as well as corrosion resistance and a slew of other practical benefits. Although aluminum is not the strongest of metals, alloying it with other metals, such as copper, magnesium, tin or zinc, helps increase its strength, durability and mass.
Aluminum alloys are easily workable, but, as with any fabrication material, there are disadvantages of which to be aware. On one hand, cast aluminum products are relatively low cost due to aluminum’s low melting point. On the other hand, they have lower tensile strengths.
Additionally, aluminum alloys warp at high temperatures. They have lower fatigue limits than steel and weaken with repeated stress, which is why aluminum alloys are rarely used in high fatigue tolerance applications, such as girders in building construction and railways.
While the industrial benefits of aluminum are impressive – they’re recyclable, corrosion resistant, lightweight and energy efficient, and they offer military-grade durability – aluminum poses a unique set of challenges for metalworkers. In terms of pre- or post-welding problems, aluminum shares some common ground with steel, but not always.
Aluminum conducts heat six times faster than steel and has a low melting point, making it very susceptible to warping and burn-through. Aluminum wire has relatively low tensile strength, which can pose wire feeding issues and lead to weld defects if the correct equipment is not used. Common aluminum weld defects are spatter, porosity, cracking and lack of fusion.
Fortunately, there are plenty of methods to overcome the challenges that aluminum can present. Ceramic pre-weld coating technologies are among the latest powerful tools in the arsenal for solutions for aluminum metalworkers. As with steel, weld spatter can be problematic in aluminum welds. If hot spatter fuses to welding nozzles and tips, the resulting clog inhibits shielding gas from flowing freely. Poor gas flow can cause porosity, inconsistent welds or welds that require complete reworking.
Applicators, such as the E-Weld Nozzle from Walter Surface Technologies Inc., are able to coat welding nozzle surfaces and prevent spatter adherence and nozzle obstructions. This allows shielding gas to flow freely, consistent heating of the feeding wire and, ultimately, better quality welds.
Along with torch nozzles, workpieces should also be protected from spatter to ensure clean welds and eliminate costly reworks. Anti-spatter emulsions, such as Walter’s E-Weld 4, are compatible with aluminum, stainless steel and steel and can provide porosity-free welds and help prevent weld cracking. Crucially, E-Weld 4 retracts in the presence of heat, leaving welding areas free of liquid.
In addition to anti-spatter products, other measures can be taken to optimize aluminum metalworking conditions. The value of pre-weld aluminum cleaning cannot be understated. Bad shielding gas or bad wire can cause porosity, but so can a lack of pre-weld cleaning.
Two steps come into play: First, it is crucial to remove all oils, greases, lubricants, solvents and other hydrocarbons from the base material in the weld area. These contaminants contain hydrogen, and if they get into the welding arc, they cause weld porosity. Powerful degreasers designed for aluminum and sensitive alloys help remove contaminants.
Second is the removal of oxides from weldable surfaces. This can be done with a stainless steel power brush with fine bristles. It requires a light touch; excessive pressure actually burnishes oxides and drives them into the aluminum surface.
Pre-weld products that eliminate fabrication problems such as porosity or cracking are common. But what about post-weld problems such as discoloration, weld smut or heat tint on heat-affected zones?
For post-weld processes, electrochemical weld cleaning technologies make sense. Where aluminum cleaning is concerned, there’s been a move away from traditional wire brushes and harsh chemical cleaning solutions in favor of efficient, environment-friendly electrochemical technologies.
Wire brushes are fast but can scratch aluminum and alter finishes. Strong chemicals (pickling pastes) can clean welds, but, depending on the type, cause surface damage. Health hazards and expensive disposal issues also come into play.
Walter’s Surfox is an electrochemical system that doesn’t damage aluminum or stainless steel. On a fresh aluminum weld, it is not uncommon to see the presence of black smut – a residue that needs to be cleaned. And metalworkers want fast cleaning processes that won’t alter surfaces.
The Surfox 305 cleans a weld at a rate of 3 ft. to 5 ft. per min. The device uses a pH-neutral electrolyte solution, pumped directly to the surface being cleaned, and the dynamic electrical current control prevents micro pitting on weld surfaces.
Compare that with toxic pickling pastes, which require at least an hour of application prior to removal. In addition to the time involved, pickling pastes contain strong acidic solutions of nitric and hydrofluoric acids. Costly environmental compliance measures come into play if special wastewater disposal techniques are required, which usually are with toxic acids. Electrochemical weld cleaning makes more economic, environmental and safety sense than costlier, traditional and sometimes toxic methods.
Working with aluminum alloys can throw up all manner of shop floor challenges – be they pre-weld or post-weld. Fabricators looking to prevent pre-weld defects, however, can find solutions. For those seeking safe and efficient post-weld methods to remove heat tint and discoloration from MIG, TIG and spot welds, electrochemical cleaning and polishing technologies offer approaches toward correcting weld defects in an environment friendly manner.