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INTRODUCTION

MAGNESIUM is the lightest structural metal representing an attractive option for aerospace and transport industries, providing that limitations such as poor corrosion resistance and low mechanical strength at room and high temperature can be overcome. Rare-earth containing magnesium alloys have received considerable attention due to their potential for improving strength and creep resistance at high temperatures.[1–7] Especial interest has been paid to Mg-Y,RE-Zn systems due to the thermal stability of second intermetallic phases formed during processing. These phases enhance its mechanical strength and forming ability due to the anisotropy, commonly found in magnesium alloys after extrusion or rolling stages, diminishes by weakening the basal texture. Based on the RE/Zn ratio, several second phases are reported.[8–17] For a (Y, Gd, Dy, Ho, Er, Tb, and Tm)/Zn ratio around 2, the alloy microstructure consists of magnesium dendrites and Long-Period Stacking Ordered (LPSO) phases. LPSO phase-containing magnesium alloys can combine high strength with acceptable ductility and enhanced creep resistance. LPSO phases are ordered solid solutions of yttrium or rare-earth elements and transition metals in the magnesium lattice, where these atoms are arranged periodically in the magnesium basal planes and change the periodicity along the c direction. A Mg97Y2Zn1(pct at) alloy produced by warm extrusion of rapid-solidified ribbons exhibited high yield strength, about 610 MPa, with 5 pct of elongation at room temperature (RT).[16] Recently, Kawamura and Yamasaki[18] obtained after extrusion of ingot SANDRA CABEZA, Ph.D. Student, GERARDO GARCE´S, PABLO PE´REZ, Tenured Scientists, and PALOMA ADEVA, Professor, are with the Department of Physical Metallurgy, National Center for Metallurgical Research (CENIM-CSIC), Av. Gregorio del Amo n8, 28040 Madrid, Spain. Contact e-mail: s.cabeza@cenim. csic.es Manuscript submitted June 25, 2013. Article published online October 16, 2013 3222—VOLUME 45A, JULY 2014

Mg97Y2Zn1 alloys a combination of high yield stress (around 350 MPa) and appreciable ductility (around 8 pct), by controlling the cooling rate during the casting process and the extrusion parameters. The partial or total substitution of Y by RE elements in this system Mg-Y,RE-Zn promote the formation of b precipitates in the prismatic planes, preserving the formation of the LPSO phase, resulting in a considerable increase of the strength at RT.[18–23] There is a worldwide concern regarding RE global strategic market and their recycling. Moreover, Europe, Japan, and the USA are taking actions with guidelines for research and industry.[24,25] The aim of lowering RE additions is therefore pursued, but such reduction would imply a detriment in mechanical properties. In order to preserve the mechanical requirements with low rareearth contents, a powder metallurgy (PM) route is proposed in the present study. The advantages of processing magnesium alloys by a PM route stem from microstructure refinement, and increase in solid so