With the rapid development of human civilization, the consequent air pollution and greenhouse gas (GHG) emissions have threaten human being for years. Energy conservation and emission reduction is an increasing priority in the development of transportation industry.
Material substitution appears a promising option for lightweighting. Traditionally, steel, such as low-carbon steel and stainless steel, is used as main material to build major structure of transportation equipment. Titanium, aluminum and magnesium are promising lightweight metallic materials as alternatives to steel and cast iron. Among these materials, aluminum shows a balanced performance, such as light weight, good corrosion resistance, good formability, high specific strength and relatively low cost. Density of aluminum alloy is only one third of steel. Considering structural optimization due to material replacement, the overall weight of rail car-body is decreased by 50% when aluminum is used. This degree of reduction deserves an effort in engineering application.
Aluminum alloys was originally used in aviation industry which is an important part of the transportation industry. It was firstly used on Junker F13 fuselage with the invention of 2017-T4 alloy in 1920. It began to be used in the manufacture of train with increase of the train speed until 1980s. So far, it has been widely used in passenger cars with speeds above 200km/h, such as German ICE series high-speed EMU car-body, French ALSTOM double-decker TGV high-speed EMU car-body, Italy Pendolino(ETR) series pendulum high-speed EMU car-body, Japanese Shinkansen, and Chinese CRH high-speed EMU car-body and so on. Especially with the huge expansion of high-speed rail lines in China in the last 20 years, the development and application of aluminum alloy prospered.
The special operating environment of trains and unique properties of aluminum alloy promotes the their combination, which favored the popularization of high speed train and in-depth application of aluminum alloy in transportation industry. For engineering application on rail transit vehicles, aluminum has the following advantages:
The net weight of the vehicle can be greatly reduced. The use of aluminum alloy can greatly reduce the net weight of rail passenger car while it meets the safety requirements in the aspect of strength and rigidity. Generally speaking, car-body made of aluminum alloy is 30%~50% lighter than that of steel. For high-speed and double-deck trains, the most effective way to make vehicles light is to increase the proportion of aluminum used in vehicles as much as possible.
Aluminum alloy has excellent fire resistance. Although the melting point of aluminum (660 °C) is much lower than that of steel (1530 °C), the fire-resistant of the car body is not only related to the melting point of the material, but also to the thermal conductivity of the material. Compared with steel, aluminum alloy has excellent thermal conductivity and better heat dissipation.
Aluminum alloy has good corrosion resistance. The surface of aluminum alloy is easy to form a layer of dense oxide film, which has a good anti-oxidation ability in the atmosphere. Therefore, car-body made of aluminum alloy has better corrosion resistance than that of steel, especially in the components that are not easy to be coated, such as the box structure and some of its internal beams and columns, aluminum counterpart show obvious advantages. At the same time, aluminum alloy surface can be colored, painted, sprayed, through chemical methods to greatly improve the corrosion resistance of the components, together with improved decorative effect.
Aluminum alloy is easy to process, manufacture and maintain. With the development and application of large hollow and complex section aluminum profiles, aluminum welding technology is constantly improving, and vehicle manufacturing technology is becoming more and more mature. Aluminum alloy parts is easy to be replaced, and suitable for all kinds of surface treatment. The workload need for manufacturing rail car-body is also greatly reduced than the steel one.
The price of aluminum alloy is moderate. The high price of aluminum material increases the manufacturing cost of vehicles, but aluminum alloy also makes vehicles light, which leads to the increase of transport capacity, reduction of energy consumption and reduction of maintenance costs. Taking the comparison of maintenance hours of vehicles leaving the factory at 10 A as an example, steel car is 100%, aluminum car is 52%.The recovery value of scrapped vehicles is 100% for steel vehicles and 480% for aluminum vehicles. From the perspective of comprehensive economic benefits, the use of aluminum vehicles is economical and reasonable. Therefore, the final cost of using aluminum alloy is moderate.
