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Steel-Magnesium Laminated Composites by Infiltration Arda Çetin1*, Jérôme Krebs1, Alexandre Durussel1, 2, Andreas Rossoll1, Junya Inoue2, Shoichi Nambu2, Toshihiko Koseki2, Andreas Mortensen1 1

Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory for Mechanical Metallurgy, CH-1015 Lausanne, Switzerland 2 Department of Materials Engineering, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan ABSTRACT Steel–magnesium alloy laminated composites can be produced by gas-driven pressure infiltration of a molten magnesium alloy between layers of stacked steel sheets followed by directional solidification of the infiltrated magnesium alloy. A key step in the process is ensuring adequate separation and alignment of the steel sheets during the process; this is achieved by introducing small dimples in the steel sheets to hold them apart during infiltration. Advantages of the process are its speed, the defect-free composites it produces, and the fact that, unlike roll-bonded composites, the steel in the composite is in an annealed condition. The ultimate tensile strength of the as-cast laminates, of 260 MPa, obeys the rule of mixtures. The uniform tensile elongation, of around 20%, makes the infiltrated laminates nearly as ductile as the bulk steel it contains, implying that the magnesium alloy in the as-cast laminates has a substantially increased tensile ductility in comparison to the bulk state in a metallurgically equivalent condition. INTRODUCTION Lamination is a strategy, used well over a millennium, to drive certain metals and alloys to perform well beyond their performance range [1-5]. A brittle metal, for example, can experience large tensile strains when bonded to a ductile metal [6, 7] as long as the interfaces are strong enough to resist delamination. The reason is that, if the two metals are strongly bonded together, the more ductile metal will prevent necking in the other, less ductile, metal thus coaxing it to deform beyond the tensile strain that it would reach in its metallurgically equivalent bulk state [3-12]. Magnesium and its alloys tend to display poor ductility since they have only a few slip systems in their hexagonal crystal structure. Lamination could therefore be a promising strategy to improve their performance, notably where deformability is required. To this end, bonding magnesium to a more ductile metal, such as steel, can be attractive, also because magnesium is relatively inert in contact with iron. Chemical compatibility of various magnesium alloys with iron has already been investigated [5, 13, 14]; however, none of those studies concern laminated structures.

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In what follows, we show how infiltration can be used to produce laminated metal composites (LMCs) of mild steel and a manganese and zinc containing magnesium alloy, and explore their structure and tensile properties. A more complete report of this work can be found in Ref. [1] EXPERIMENT The LMCs were made by infiltration of ZM21 magnesium alloy, a zinc and manganese containing magnesium alloy, into a sta