Creep processes in magnesium alloys and their composites
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INTRODUCTION
THE major current area of growth for the use of magnesium alloys is in the high volume commercial automotive sector, where there is an incentive for weight savings to maximize fuel economy and minimize emissions.[1] To achieve additional substantial increases in the use of magnesium in the automotive industry, it is necessary to utilize magnesium alloys in the engine and transmission components.[1–5] These applications require a greater improvement in the high-temperature strength and creep resistance than is possible with the currently available commercial magnesium alloys.[6] Here, cost considerations dictate major compromises on alloy additions and performance. In practice, the creep resistance of magnesium alloys tends to be limited at temperatures above ⬃400 K. However, there is a potential for achieving a considerable improvement in the creep properties of magnesium alloys through the inclusion of nonmetallic reinforcements to form metal matrix composites (MMCs). A fundamental issue in the creep behavior of these composites is a determination of the mechanism or mechanisms by which the creep rate of the composite is reduced through reinforcement of the creeping matrix with lesscreeping or non-creeping short fibers or particles. When this creep mechanism is clarified, it may be possible to design new MMCs with even higher creep resistance by tailoring the constituent parameters of the matrix alloy and the short fiber or particle phase. Although the creep properties of complex magnesium alloys have been extensively investigated and discussed,[6–17] comparatively little research has been carried out on the ´ , K. KUCHAR˘OVA ´, V. SKLENIC˘KA, Professor, and M. PAHUTOVA and M. SVOBODA, Senior Scientists, are with the Institute of Physics of Materials, Academy of Sciences of the Czech Republic, CZ-616 62 Brno, Czech Republic. T.G. LANGDON, Professor, is with the Departments of Aerospace & Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. METALLURGICAL AND MATERIALS TRANSACTIONS A
creep behavior of Mg-based fiber or particulate-reinforced composites[18–29] and their microstructure evolution.[23,28–33] Therefore, the present study was initiated to conduct experiments on two representative magnesium alloys (AZ 91 and QE 22) and their composites in order to compare directly their creep resistance. The objective of this research is thus to provide information on the significance of creep strengthening in discontinuously reinforced magnesium alloys and to con
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