《Unexpected influence of Mn addition on the creep properties of a cast Mg–2Al–2Ca (mass%) alloy》.pdf

Available online at Acta Materialia 59 (2011) 7662–7672 /locate/actamat Unexpected influence of Mn addition on the creep properties of a cast Mg–2Al–2Ca (mass%) alloy T. Homma a,⇑, S. Nakawaki a, K. Oh-ishi a, K. Hono b, S. Kamado a a Department of Mechanical Engineering, Nagaoka University of Technology, Nagaoka 940-2188, Japan b National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan Received 5 April 2011; received in revised form 24 August 2011; accepted 30 August 2011 Available online 15 October 2011 Abstract The addition of 0.3% Mn to a Mg–2Al–2Ca (mass%) alloy improves the minimum creep rate by one order of magnitude compared with the Mn-free alloy. Network-shaped Mg Ca (C14 structure) and (Mg,Al) Ca (C36 structure) compounds coexist in the interdendritic 2 2 regions, while plate-shaped Al2Ca (C15 structure) phases are dispersed in the matrix. Ordered Guinier–Preston (GP) zones form dynam- ically on the basal plane of the a-Mg matrix during creep deformation. The number density of the fine GP zones in the Mn-containing alloy was found to be higher than that in the Mn-free alloy. 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Magnesium alloy; Creep; Guinier–Preston zone; Transmission electron microscopy; Atom probe 1. Introduction systems are ACM522 [6] and MRI153 [7], both of which