Enabling sustainable transportation through joining of dissimilar lightweight materials
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uction In 2016, people in the United States travelled more than 5.7 trillion miles in cars, trucks, buses, trains, and airplanes. In the same year, 14.9 million tons of freight were moved in the United States via road, rail, water, and air.1 However, all of this movement comes at a cost. In 2017, the transportation sector became the largest contributor to greenhouse gas emissions in the United States at 29% of the total 6.5 million metric tons of CO2 equivalent emitted.2 Because it takes less energy to move a lighter object, even small reductions in weight can have a significant effect on fuel consumption and emissions in the transportation sector. Historically, ships, trains, trucks, and cars have been made of steel, which is a low-cost product with an established supply chain and manufacturing infrastructure. Dozens of steel grades are commercially available in product forms such as coils, plates, and ingots that can be manufactured in a variety of processes, including casting, forging, sheet forming, and roll forming to turn the steel into components. High volume
assembly of steel components into vehicles primarily utilizes various forms of fusion welding, including arc welding with different shielding strategies, laser welding, and resistance welding. Fusion welding creates a metallurgical bond between the steel components via localized melting and results in a weldment that can have mechanical properties equivalent to the component steel. However, mild carbon steel has a density of 7.85 g/cc, which can result in substantial weight when fabricating large structures. Airplanes have embraced lightweight materials since the Wright brothers built the Wright Flyer from wood and canvas with an aluminum engine in 1903. The huge increase in aluminum production during World War II allowed for more modern aircraft designs. Boeing’s 737 aircraft, designed in 1965 and still one of the most popular commercial airplanes, is made of 81% aluminum. Aircraft structures are primarily assembled using aluminum rivets, although steel rivets are also used when joining steel components to avoid galvanic corrosion. While the cost per pound of aluminum is approximately four
Sarah Kleinbaum, US Department of Energy Vehicle Technologies Office, USA; [email protected] Cindy Jiang, AET Integration, Inc., USA; [email protected] Steve Logan, AET Integration, Inc., USA; [email protected] doi:10.1557/mrs.2019.178
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Enabling sustainable transportation through joining of dissimilar lightweight materials
times that of mild steel, it is also approximately one-third the density of steel. There are dozens of grades of aluminum alloys spanning a wide range of properties, which makes aluminum appealing
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