condition within the material that can produce intergranular microcracking, which may be susceptible to propagation and eventual failure of the welded component. Fabricators may get into this predicament when they ask their material supplier for a “high-strength alloy.” They often receive 7075 or 2024 because they are “aerospace” alloys. Unfortunately, ASM International classifies both of these alloys as nonweldable. To solve the problem, we recommended fabricating the boxes from 2219. It offers high strength and can be welded using 2319 filler as the weld strength needed to be as close to the base material strength as possible. There are hundreds of grades of aluminum, and any one of them might be found on an airplane. However, there’s no such thing as “aircraft-quality” welding on aluminum. Outside of the beverage cart and seat frames, planes do not use arc welded aluminum structures. For example, wings are made from 7075 and 2024. As noted, both grades are nonweldable. For this reason, never attempt arc welding repair on a 7075 or 2024 component. Be aware, more than a few metal suppliers use “aerospace-grade” as a marketing ploy. Don’t take the phrase aerospace-grade at face value. Fabricators should ask for the specific grade of material, and then determine if it’s weldable and which filler metal best matches the application. For example, 6061 often gets marketed as an aerospace grade material, and as noted earlier, 6061 is easily welded using a host of filler materials. Go Big We often see fabricators trying to perform the welding equivalent of towing a 30-ft trailer with a subcompact car. For example, one fabricator wanted to weld 1⁄2-in.-thick aluminum using a conventional 250-A, AC/DC GTAW power source and 1⁄16-in. filler rod. A better solution would be to use a 350-A advanced inverter-based power source and 1⁄8-in. filler rod. Note the 1⁄8-in. rod has four times the volume of a 1⁄16-in. rod. Whenever operators are GTA welding aluminum and the pool becomes uncontrollable — yet they know they need to apply sufficient amperage to obtain penetration — that’s a signal to Fig. 4 — Modified pulsed spray transfer processes produce good bead aesthetics without gun manipulation. More significantly, they enable using a single wire diameter use a larger-diameter filler rod. When dipped into the weld pool, the larger rod will absorb more heat and provide better pool control. When it comes to GMAW, we see fabricators trying to weld sections 0.250 in. and thicker with a 250-A, 40% duty cycle conventional power source and 0.047-in. wire, which has a maximum energy capacity of about 240 A/28 V. Given the general rule of using 1 A for each 0.001 in. of material thickness, it’s clear the system isn’t optimized for this application. For thicker sections, a better choice would be to use a power source with an output of at least 350 A at a high duty cycle paired with 0.062-in. wire, which can be run up to about 340 A/30 V. Bigger Wire, Broader Range Alternatively, and often ideally, fabricators who want to weld aluminum using a GMA process should explore using an inverter power source and a pulsed spray transfer process. In many applications, the more controlled and efficient heat input of GMAW-P provides better fusion, faster travel speeds, reduced distortion, better pool control, a gas tungsten arc-like bead appearance (by using a modified GMAW-P process, such as ESAB’s SuperPulse™process), reduced spatter, and all-position welding capabilities — Fig. 4. Compared to short circuit or spray transfer, GMAW-P also enables using larger-diameter wires, as well as standardizing on a single diameter for a broad range of material thicknesses. For example, 0.047-in. wire (say in 4xxx or 5xxx series aluminum) can weld materials as thin as 0.040 in. and up to 3⁄8 in. thick; a 0.062-in. wire can weld materials as thin as 0.187 in. and up to 5⁄8 in. thick (generally speaking). Standardizing on a single diameter of wire reduces inventory costs and complexity, and larger-diameter wires cost less per pound. Costs can range between 2 and 10% from one size to the next, depending on alloy and package size. As an added benefit, the larger diameter wires possess greater columnar strength, so they typically improve wire feed performance. Ask Questions The variety of aluminum grades and filler materials is both a blessing and curse — a blessing because the welded material can be tailored to meet many different applications, and curse because the complexity of choices creates confusion and error. As a result, consider involving a knowledgeable filler metal supplier not just when selecting a filler metal, but also when selecting a base material and developing welding procedures. Remember: The only stupid question is the one you didn’t ask. WJ THOM BURNS is technical services director and ROB KRAUSE is technical services manager at AlcoTec Wire Corp., Traverse City, Mich, www.alcotec.com. AlcoTec is a subsidiary of ESAB Welding and Cutting Products, Florence, S.C.; www.esab.com. APRIL 2015 / WELDING JOURNAL 45 for a broad range of metal thicknesses.
Welding Journal | April 2015
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