Investigation into the Extrudability of a New Mg-Al-Zn-RE Alloy with Large Amounts of Alloying Elements
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SINCE the beginning of this century, magnesium alloys, the lightest structural metallic materials, have attracted great attention for applications in 3-C (computers, communications, and consumer electronics) products, automobiles, and aerospace in order to realize weight reduction.[1–6] Cast magnesium alloy parts made using a variety of casting techniques have been widely accepted for these applications.[7] However, the applications of wrought magnesium alloys have been rather limited, although in general wrought magnesium alloys possess better mechanical properties than their cast counterparts and are thus more suitable for structural applications.[8,9] Extruded magnesium alloy products, for example, accounted for less than 3 pct of the annual output of magnesium production in 2013.[10] The limited applications of extruded products are mainly due to the
SHENG-WEN BAI and GANG FANG are with the State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China. Contact email: [email protected] JIE ZHOU is with the Department of Biomechanical Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands. Manuscript submitted September 17, 2018. Article published online May 17, 2019 3246—VOLUME 50A, JULY 2019
low extrudability of magnesium alloys, compared to aluminum alloys, leading to low productivity and low cost-effectiveness. The limited use of extruded magnesium alloy products is also due to the achievable mechanical properties that are not substantially better than those of the cast counterpart. In recent years, much research effort has been made to improve the mechanical properties and extrudability of magnesium alloys. Basically, there are two ways to improve the mechanical properties of extruded magnesium alloys. Alloying is effective in enhancing the mechanical properties of magnesium, but at the same time, it imposes limitations to applicable extrusion speed, as a result of raised resistance to hot deformation, increased temperature during the process, and lowered incipient melting point. Microstructure control throughout materials processing from casting to extrusion is also effective, especially the control of grain structure within an applicable extrusion process window by applying an optimum combination of extrusion process parameters. Obviously, it is best if alloying and microstructure control are combined to achieve optimum mechanical properties from a refined grain structure and from the distribution of fine precipitates at a minimum loss in extrusion speed. The effect of alloying on the microstructure, extrudability, and mechanical properties of extruded magnesium alloy products depends on the amount of a chosen element and its solubility in the magnesium matrix. METALLURGICAL AND MATERIALS TRANSACTIONS A
When its content is low, it stays dissolved in the magnesium matrix even at room temperature, creating a solid solution strengthening effect. However, when the content exceeds its solubility in the magnesium matrix,
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