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Deburring/Finishing

Walter Surface Technologies: Working with aluminum, as workpiece or welding wire, poses challenges for welders

By Jonathan Douville

November 2018 - Aluminum’s high strength-to-weight ratio makes it an obvious choice for automotive and aerospace applications, and although it is not the strongest of metals, alloying aluminum with other materials, particularly copper, magnesium, tin and zinc, helps increase its strength, durability and mass.

These aluminum alloys are easily workable but, as with any material, there are fabrication advantages and disadvantages. On one hand, cast aluminum products are relatively inexpensive due to aluminum’s low melting point. On the other, they have lower tensile strengths. Additionally, aluminum alloys will 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 applications that require a high fatigue tolerance, such as girders in building construction and railways.

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Shop floor challenges

Aluminum can pose a unique set of challenges for metalworkers. In terms of pre- or post-welding problems, aluminum shares some common ground with steel; however, 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 incorrect equipment is used. Common aluminum weld defects are spatter, porosity, cracking and lack of fusion.

Defects such as porosity or cracking are common concerns. When welding, if hot spatter fuses to nozzles and tips, the resulting clog inhibits shielding gas from flowing freely, which can cause porosity, inconsistent welds or welds that require complete reworking. Applicators such as Walter Surface Technologies’ E-Weld Nozzle coat welding nozzle surfaces and prevent spatter adherence and nozzle obstructions. Beyond torch nozzles, workpieces can also be protected from spatter to ensure not only clean welds but also eliminate costly reworks. E-Weld 4 is a premium anti-spatter emulsion that protects workpieces from spatter.

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Aluminum alloys are easily workable but, as with any fabrication material, there are advantages and disadvantages.

In addition, welders working with aluminum should not underestimate the value of pre-weld cleaning. First, it is crucial to remove all oils, greases, lubricants, solvents and other hydrocarbons from the base material in the aluminum weld area. These contaminants contain hydrogen, so if they get into the welding arc, they cause weld porosity.

Premium degreasers, such as Walter’s Alustar products, remove contaminants from the weld area. Additionally, Walter’s CB 100 ALU is a powerful degreaser designed for aluminum and sensitive alloys. These degreasers are biodegradable so there is no added cost for disposal. Second, it is necessary to remove oxides from weldable surfaces. This can be done with a stainless-steel power brush with fine bristles, but operators are advised to use a light touch. Excessive pressure will actually burnish oxides and drive them into the aluminum surface.

Post-weld cleanup

But what about post-weld problems such as discoloration, weld smut or heat tint on heat-affected zones? Where aluminum cleaning is concerned, there’s been a move away from traditional wire brushes and harsh chemical cleaning solutions in favor of efficient, environmentally friendly electrochemical technologies.

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Common causes of incomplete fusion include inadequate oxide removal, insufficient heat input, narrow joint preparation and improper torch angle.

Wire brushes are fast but can scratch aluminum and alter its finish. Strong chemicals (pickling pastes) can clean welds but can cause surface damage. Health hazards and expensive disposal issues also are a concern when using chemicals. Walter’s Surfox is a safe, electrochemical and pH-neutral solution that won’t damage aluminum or stainless steel.

When grinding or cutting aluminum, it is important to use high-performance equipment that won’t add unnecessary steps to jobs. Walter’s Enduro-Flex Alu flap discs can be used to blend or finish aluminum alloys. Long lasting, the discs feature a special abrasive blend and size that provides smooth and fast material removal. Metalworkers will spend more time getting the job done and less time making trips to the tool crib.

Walter’s Alu grinding and cutting wheels won’t clog or glaze when working with aluminum and other nonferrous metals. Because they are free of waxes and lubricants, there is no need to clean work surfaces or apply a coating before welding, which saves valuable preparation time.

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The Surfox 305 weld cleaning system removes heat tint from heat-affected zones of MIG, TIG and spot welds.

Once an aluminum alloy shape is free of defects, finished to a professional standard, electrochemically cleaned and looking its best, shops then may need to mark or  brand the piece. Surfox marking and etching kits use an efficient electrochemical process that permanently marks and etches aluminum and stainless steel surfaces. The technology involves a wand that connects directly into Surfox electrochemical cleaners to permanently mark or etch parts, model or serial numbers, company logos, lot and batch numbers, UPC codes, QR codes, and more.

In terms of cutting, blending and polishing aluminum alloys, there has never been a better range of high-tech choices to enhance productivity and maximize safety on today’s shop floor. FFJ

Jonathan Douville is senior product manager, R&D International, at Walter Surface Technologies. Prior to joining Walter in 2012, Douville was senior scientist, R&D, at Johnson & Johnson. He has experience in mechanical and industrial engineering, R&D, product design, process engineering, mechatronics and medical devices.

Sources

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