Production and Mechanical Properties of Roll Bonded Bulk Metallic Glass/Aluminum Laminates
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BULK metallic glasses (BMGs) are alloys that can form an amorphous structure at thicknesses greater than 1 mm, when produced via copper mold casting techniques. The critical thickness of a BMG is a measurement used to assess the glass forming ability of the alloy. The critical thickness of an alloy is the largest cross section of a casting that can be produced with a 100 pct amorphous structure.[1] When casting a BMG, the critical thickness cannot be exceeded in any direction to maintain an amorphous structure. This limits the size and shape of parts that can be made from BMGs. The limit in cross-sectional thickness also limits the length of a part that can be made, because of the limits of molten metal flow through a thin cross section mold. To overcome the restrictions on part length continuous casting techniques such as twin roll casting can be used. Twin roll casting involves the delivery of molten metal through a melt delivery nozzle to the roll nip of two counter rotating rolls. Twin roll casting has been DANIEL EAST, Research Engineer, is with the Department of Materials Engineering, Monash University, Clayton, VIC 3800, Australia, and also with the CSIRO Process Science and Engineering, Clayton, VIC 3168, Australia. Contact e-mail: [email protected] MARK A. GIBSON and DANIEL LIANG, Research Scientists, are with the CSIRO Process Science and Engineering. JIAN-FENG NIE, Professor, is with the Department of Materials Engineering, Monash University. Manuscript submitted May 31, 2012. Article published online September 27, 2012 2010—VOLUME 44A, MAY 2013
used to produce sheet in Zr- and Mg-based amorphous systems.[2,3] The major shortcoming of magnesium-based BMGs is their low level of toughness. By combining a second ductile phase into a hybrid structure, the toughness levels can be increased substantially. This second phase toughening mechanism has been achieved via semi-solid processing in Zr-and Ti-based systems.[4,5] Mg-based BMG systems also have compositions that form in-situ second phases, and research is being conducted to exploit these systems for improved mechanical performance of bulk amorphous alloys.[6,7] Ex-situ methods of adding second phases to an amorphous matrix have also been trialled. The addition of tungsten wire as structural reinforcement has been tried with Zr-based amorphous materials.[8] As with the previous reinforcement methods, the wires act to restrict shear band propagation and to promote the generation of multiple shear bands. In this work laminate structures are produced via roll bonding to produce an Mg-based BMG/aluminum laminate. The lack of toughness in BMGs has been highlighted as an obstacle to the use of BMGs as structural materials. Laminate structures have been used to improve the impact resistance of BMGs. To date the work done on production of laminate structures involves the use of press forming and forge casting. Crystalline metal and amorphous metal are bonded in layers to form laminates to improve the toughness of the material. In these two techniques the BMG is
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