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What is aluminum?
What happens to aluminum when it enters the environment? How might I be exposed to aluminum? How can aluminum affect my health? How likely is aluminum to cause cancer? How can aluminum affect children? How can families reduce the risks of exposure to aluminum? Is there a medical test to determine whether I’ve been exposed to aluminum? Has the federal government made recommendations to protect human health? What does ductile and malleable mean? Because it is a good conductor of heat, aluminum is used to make what two items? Why is my aluminum weld much weaker than the parent material? What type of shielding gas should I use for aluminum welding? For TIG Welding, what type of electrode is best for aluminum? How much preheat should I use when welding aluminum? What is the proper stress relieving practice for aluminum welds? How can I tell different aluminum alloys apart? How do I TIG weld two dissimilar thicknesses of aluminum? How do I weld 7075? What is the difference between aluminum and vinyl siding? Is aluminum siding more durable than vinyl? Can I paint over aluminum siding? What are the advantages to aluminum siding? |
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What is aluminum? Aluminum is the most abundant metal in the earth’s crust. It is always found combined with other elements such as oxygen, silicon, and fluorine. Aluminum as the metal is obtained from aluminum-containing minerals. Small amounts of aluminum can be found dissolved in water. Aluminum metal is light in weight and silvery-white in appearance. Aluminum is used for beverage cans, pots and pans, airplanes, siding and roofing, and foil. Aluminum is often mixed with small amounts of other metals to form aluminum alloys, which are stronger and harder. Aluminum compounds have many different uses, for example, as alums in water-treatment and alumina in abrasives and furnace linings. They are also found in consumer products such as antacids, astringents, buffered aspirin, food additives, cosmetics, and antiperspirants. What happens to aluminum when it enters the environment? * Aluminum cannot be destroyed in the environment, it can only change its form. * In the air, aluminum binds to small particles, which can stay suspended for many days. * Under most conditions, a small amount of aluminum will dissolve in lakes, streams, and rivers. * It can be taken up by some plants from soil. * Aluminum is not accumulated to a significant extent in most plants or animals. How might I be exposed to aluminum? * Virtually all food, water, air, and soil contain some aluminum. * The average adult in the U.S. eats about 7-9 mg aluminum per day in their food. * Breathing higher levels of aluminum dust in workplace air. * Living in areas where the air is dusty, where aluminum is mined or processed into aluminum metal, near certain hazardous waste sites, or where aluminum is naturally high. * Eating substances containing high levels of aluminum (such as antacids) especially when eating or drinking citrus products at the same time. * Children and adults may be exposed to small amounts of aluminum from vaccinations. * Very little enters your body from aluminum cooking utensils. How can aluminum affect my health? Only very small amounts of aluminum that you may inhale, ingest, or have skin contact with will enter the bloodstream. Exposure to aluminum is usually not harmful, but exposure to high levels can affect your health. Workers who breathe large amounts of aluminum dusts can have lung problems, such as coughing or abnormal chest X-rays. Some workers who breathe aluminum dusts or aluminum fumes have decreased performance in some tests that measure functions of the nervous system. Some people with kidney disease store a lot of aluminum in their bodies and sometimes develop bone or brain diseases which may be caused by the excess aluminum. Some studies show that people exposed to high levels of aluminum may develop Alzheimer’s disease, but other studies have not found this to be true. We do not know for certain whether aluminum causes Alzheimer’s disease. Studies in animals show that the nervous system is a sensitive target of aluminum toxicity. Obvious signs of damage were not seen in animals after high oral doses of aluminum. However, the animals did not perform as well in tests that measured the strength of their grip or how much they moved around. We do not know if aluminum will affect reproduction in people. Aluminum does not appear to affect fertility in animals. How likely is aluminum to cause cancer? The Department of Health and Human Services (DHHS) and the EPA have not evaluated the carcinogenic potential of aluminum in humans. Aluminum has not been shown to cause cancer in animals. How can aluminum affect children? Children with kidney problems who were given aluminum in their medical treatments developed bone diseases. It does not appear that children are more sensitive to aluminum than adults. We do not know if aluminum will cause birth defects in people. Birth defects have not been seen in animals. Aluminum in large amounts has been shown to be harmful to unborn and developing animals because it can cause delays in skeletal and neurological development. Aluminum is found in breast milk, but only a small amount of this aluminum will enter the infant’s body through breastfeeding. How can families reduce the risks of exposure to aluminum? * Since aluminum is so common and widespread in the environment, families cannot avoid exposure to aluminum. * Avoid taking large quantities of aluminum-containing antacids and buffered aspirin and take these medications as directed. * Make sure all medications have child-proof caps so children will not accidentally eat them. Is there a medical test to determine whether I’ve been exposed to aluminum? All people have small amounts of aluminum in their bodies. Aluminum can be measured in blood, bones, feces, or urine. Urine and blood aluminum measurements can tell you whether you have been exposed to larger-than-normal amounts of aluminum. Measuring bone aluminum can also indicate exposure to high levels, but this requires a bone biopsy. Has the federal government made recommendations to protect human health? The EPA has recommended a Secondary Maximum Contaminant Level (SMCL) of 0.05–0.2 milligrams per liter (mg/L) for aluminum in drinking water. The SMCL is not based on levels that will affect humans or animals. It is based on taste, smell, or color. The Occupational Health and Safety Administration (OSHA) has limited workers' exposure to aluminum in dusts to 15 milligrams per cubic meter (mg/m3) (total dust) and 5 mg/m3 (respirable fraction) of air for an 8-hour workday, 40-hour workweek. The Food and Drug Administration (FDA) has determined that aluminum used as food additives and medicinals such as antacids are generally safe. What does ductile and malleable mean? Because it is a good conductor of heat, aluminum is used to make what two items? 1. Why is my aluminum weld much weaker than the parent material? In steels a weld can be made as strong as the parent material, but this is not the case with aluminum. In almost all instances, the weld will be weaker than the parent material. To further understand why this occurs, let's look at the two classifications of aluminum alloys: heat treatable and non-heat treatable. The latter category is hardened only by cold working which causes physical changes in the metal. The more the alloy is cold worked the stronger it gets. But, when you weld an alloy that has been cold worked, you locally anneal the material around the weld so that it goes back to its 0 tempered (or annealed) condition and it becomes "soft". Therefore, the only time in the non-heat treatable alloys that you can make a weld as strong as the parent material is when you start with 0 tempered material. With heat treatable aluminum alloys, the last heat treatment step heats the metal to approximately 400° F. But when welding, the material around the weld becomes much hotter than 400° F so the material tends to lose some of its mechanical properties. Therefore, if the operator doesn't perform post-weld heat treatments after welding, the area around the weld will become significantly weaker than the rest of the aluminum - by as much as 30 to 40 percent. If the operator does perform post weld heat treatments, the proprieties of a heat treatable aluminum alloy can be improved. The following is a guide as to which series of aluminum alloys are heat treatable and which are not: Heat treatable series: 2000, 6000, 7000. Non-heat treatable: 1000, 3000, 4000, 5000. 2. What type of shielding gas should I use for aluminum welding? For both TIG Welding (Gas Tungsten Arc Welding or GTAW) and MIG Welding (Gas Metal Arc Welding or GMAW) use pure argon for aluminum materials up to ˝" in thickness. Above ˝" in thickness, operators may add anywhere between 25 to 75 percent helium to make the arc hotter and increase weld penetration. Argon is best because it provides more cleaning action for the arc than helium does and it is also less expensive than helium. Never use any shielding gas that contains oxygen or carbon dioxide, as this will oxidize the aluminum. 3. For TIG Welding, what type of electrode is best for aluminum? For most materials, including steel, a two percent thoriated tungsten electrode is recommended, but since aluminum is welded with AC rather than DC, the electrical characteristics are different and the amount of energy put into the tungsten electrode is higher when AC welding. For these reasons, pure tungsten or zirconiated tungsten are recommended for aluminum welding. In addition, the electrode diameter for AC welding has to be significantly larger than when using DC. It is recommended to start with an electrode that is 1/8" and adjust as needed. Zirconiated tungsten can carry more current than pure tungsten electrodes. Another helpful hint for AC welding is to use a blunt tip - the arc tends to wander around a pointed tip. 4. How much preheat should I use when welding aluminum? While a little preheat is good, too much preheat can degrade the mechanical properties of the aluminum. As was discussed earlier, the last heat treatment for heat treatable alloys is 400° F so if the operator preheats the aluminum to 350° F and holds the temperature in that range while welding, the aluminum's mechanical properties are changed. For the non-heat treatable alloys such as the 5000 series, if the operator holds the temperature even in the 200° F range - he or she can sensitize the material to stress corrosion cracking. In most cases, some preheat is acceptable to dry the moisture away from the piece, but preheat should be limited. Many inexperienced aluminum welders use preheat as a crutch. Since equipment for welding aluminum needs to operate at higher capacities, many feel that preheat helps eliminate equipment limitations, but this is not the case. Aluminum has a low melting point -- 1200° F compared to 2600° F to 2700° F for steel. Because of this low melting point, many operators think they only need light duty equipment to weld the aluminum. But, the thermal conductivity of aluminum is five times that of steel, which means that the heat dissipates very quickly. Therefore, welding currents and voltages for welding aluminum are higher than they are for steel so operators actually need heavier duty equipment for aluminum. 5. What is the proper stress relieving practice for aluminum welds? When welding, the operator sets up residual stresses around the vicinity of the weld because the molten material shrinks as it solidifies. Further, when the operator takes this welded structure and begins to remove material by machining, it tends to distort and create dimensional instability. To avoid this in aluminum, operators perform stress relieving by heating the material hot enough to allow the aluminum atoms to move around. For steel, the stress relieving temperature is approximately 1050° F to 1100° F, but for aluminum, the proper stress relieving temperature is 650° F. This means that in order for post weld stress relief on aluminum to be effective, the material will have to be heated to a temperature where mechanical properties will be lost. For this reason, post weld stress relief is not recommended for aluminum. 6. How can I tell different aluminum alloys apart? There are quite a few different aluminum alloys and for proper and safe welding, you should know what alloy your welding. If you don't, you can follow these general guidelines: * Extrusions are generally 6000 series alloys * Castings most often are a combination of aluminum/silicon cast -- some are weldable, others are not * Pieces of sheet, plate or bar are probably 5000 to 6000 series alloys If you want to be precise, purchase an alloy tester kit that will help you determine the exact makeup of your alloy. 7. How do I TIG weld two dissimilar thicknesses of aluminum? When an operator has two dissimilar thicknesses, he or she must set the parameters so that they are high enough to TIG weld the thickest piece. When welding, favor the joint and put more of the heat on the thicker piece. 8. How do I weld 7075? Most aluminum alloys are weldable, but there are a fair number of them that are not, including 7075 aluminum. The reason 7075 is singled out in this example is that it is one of the highest strength aluminum alloys. When designers and welders look for an aluminum alloy to use, many will start by reviewing a table that lists all of the aluminum alloys and their strengths. But what those newcomers don't realize is that few of the higher strength aluminum alloys are weldable - especially those in the 7000 and 2000 series - and they should not be used. The one exception to the rule of never using 7075 for welding is in the injection molding industry. This industry will repair dies by welding 7075 - but it should never be used for structural work. • What is the difference between aluminum and vinyl siding? Some of the major differences are: vinyl is an extruded plastic material while aluminum siding is a formed metal. Vinyl siding has a solid, inherent color whereas aluminum siding typically has a baked on enamel finish which can chip off. • Is aluminum siding more durable than vinyl? You might assume that because it is a metal aluminum is a more durable house siding choice than vinyl. However, vinyl usually ranges in thickness from .040 of an inch to .046" whereas aluminum siding is typically .019". Vinyl siding is usually twice as thick as aluminum siding and much less likely to be dented or bent. • Can I paint over aluminum siding? Aluminum siding usually was offered with a baked on enamel finish that can be chipped off or scratched. However, it is very easy to paint and maintains the same properties all year long despite the temperature so you will have few issues resulting from the metal expanding or contracting. • What are the advantages to aluminum siding? Aluminum siding won't expand or contract as outside temperatures change and it is extremely durable. It resists corrosion and for years has stood up to adverse weather conditions. It is frequently used for trim pieces as it is easily bent and formed on location, whereas vinyl siding must be formed by the manufacturer. |