Microstructure and compression behavior of chip consolidated magnesium
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Ritwik Basu and Indradev Samajdar Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology—Bombay, Mumbai 400076, India
Mirle K. Surappa Department of Materials Engineering, Indian Institute of Science, Bengaluru 560012, India Director, Indian Institute of Technology—Ropar, Rupnagar 140001, Punjab, India (on Deputation from Department of Materials Engineering, Indian Institute of Science, Bengaluru 560012, India) (Received 8 September 2011; accepted 14 November 2011)
Chips produced by turning a commercial purity magnesium billet were cold compacted and then hot extruded at four different temperatures: 250, 300, 350, and 400 °C. Cast billets, of identical composition, were also extruded as reference material. Chip boundaries, visible even after 49:1 extrusion at 400 °C, were observed to suppress grain coarsening. Although 250 °C extruded chip-consolidated product showed early onset of yielding and lower ductility, fully dense material (extruded at 400 °C) had nearly 40% reduction in grain size with 22% higher yield strength and comparable ductility as that of the reference. The study highlights the role of densification and grain refinement on the compression behavior of chip consolidated specimens.
I. INTRODUCTION
Chips generated during machining are a major challenge for the industry and environment. Although recycling through remelting is widely practiced (conventional technique), it is typically energy intensive and consequently expensive. Sharma and Nakagawa proposed a new method of recycling the chips and scraps through direct conversion, circumventing the melting route.1 This approach gained momentum in the 1990s when several publications appeared presenting high-strength products manufactured through recycling of machined chips.2–4 This new method has been known as solid state recycling (SSR) from the nature of its recycling route, which involves cold compaction followed by hot extrusion with or without sintering. Due to increasing usage of light metals (such as magnesium and aluminum alloys) in electronic, automotive, and aircraft industry, wastes such as chips and swarfs can be expected to become more worrisome to the industry and the environmentalists. This has led to an extensive research in improving strength properties of SSR-machined chips. Although SSR of aluminum chips is equally successful and quite a number of papers are available on this material,5–8 limited work is available on steels9 and titanium alloys10. This is possibly because recycling magnesium (Mg) alloys through this technique is more sensible, for it a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.411 J. Mater. Res., Vol. 27, No. 4, Feb 28, 2012
does away with the hazardous melting route. Mg alloys being the lightest among the structural alloys have many beneficial characteristics: high specific strength and stiffness, superior damping capacity, high thermal conductivity, high dimensional stability, good electromagnetic shielding
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