While magnesium alloys have the attractive attributes of low density, the application of the metal in transportation industries has been restricted by its low stiffness and strength. The aim of this study was to examine the possibility of lightweight railway car body construction using magnesium alloys from the structural and manufacturing perspectives. Extruded members, making up a car body, were designed employing a gradient-based optimization algorithm. And then, numerical simulations were conducted to confirm the structural performance of the newly designed car body. In addition, one of the designed members was extruded and joined with another via friction stir welding in order to verify its fabrication potential. The work demonstrated that, with just 85% of the weight of an aluminium car body currently in operation, a magnesium-based railway car body can be potentially constructed by extrusion followed by friction stir welding for the next generation rolling stocks; that is to say, the weight saving amount is 10% of the total bare frame weight, or 2% of its total rolling stock weight.

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서 론자동차Abstract In this study, the optimal welding condition of an extruded AZ61 magnesium alloy plate was investigated through evaluation of the mechanical properties and microstructure in the friction stir welding zones. The friction stir welding conditions considered in this study were the tool rotation speeds of 400, 600, and 800rpm and the welding speeds of 200, 300, and 400mm/min. To evaluate the welding strength, tensile and hardness tests were carried out.Microstructures of the welded regions were examined using optical microscopes. Under a tool rotation speed of 800rpm and welding speed of 200mm/min, the joint showed the best joining properties. The UTS, yield strength, and elongation of the welded region showed values of 79.0%, 65.4%, and 30.1%, respectively, of those of the base metal.

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