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I.

INTRODUCTION

LOW density bulk metallic glasses (BMGs) in Ca-Mg-Zn, Ca-Mg-Cu, and Ca-Mg-Zn-Cu systems have recently been developed.[1–10] These metallic glasses represent a new group (seventh group by Takeuchi and Inoue [11]) of BMGs. They are based on two simple metals (Ca and Mg), while all other BMGs rely on transition metals. The Ca-based glasses have low density (~2000 kg/m3) and their YoungÕs modulus values (~20 to 35 GPa) are comparable to the modulus of human bones.[12] Many of these BMGs have high glass forming ability (GFA), and fully amorphous plates and rods with thickness or diameter larger than 10 mm can be easily produced by casting.[8–10] Although Ca-Mg-ZnCu glasses have a wide super-cooled liquid temperature range (DTx = Tx – Tg ~30 to 70 K), they have low glass transition temperature (Tg ~373 to 423 K) and crystallization temperature (Tx ~403 to 453 K), i.e., low glass stability (GS) against crystallization near room temperature. The ternary Ca-Mg-Zn and Ca-Mg-Cu glassy alloys also have marginal oxidation and corrosion resistance.[13–15] Quaternary Ca-Mg-Zn-Cu BMGs have better oxidation and corrosion resistance, which improves even further with addition of Al.[15] Partial substitution of Cu or Zn with Al also reduces the density of these alloys. Estimations show that every 1 at. pct Al added in place of Zn will reduce the density in Ca-MgZn alloys by ~1 pct. Unfortunately, there are no data available on the effect of Al addition on GFA and GS of Ca-Mg-Zn-Cu metallic glasses. O.N. SENKOV, Senior Scientist, and J.M. SCOTT, Materials Scientist, are with the UES, Inc, Dayton, OH 45433, USA. D.B. MIRACLE, Senior Scientist, is with the Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, Dayton, OH 45433, USA. Contact e-mail: oleg.senkov@ wpafb.af.mil The article is based on a presentation given in the symposium entitled ‘‘Bulk Metallic Glasses IV’’ which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee. Article published online July 18, 2007 METALLURGICAL AND MATERIALS TRANSACTIONS A

In the present work, we produced several new CaMg-(Al,Zn),* Ca-Mg-Al-Cu, and Ca-Mg-(Al,Zn)-Cu *Al and Zn are included in parentheses to indicate that they occupy the same structural sites, as discussed in Section III–D.

BMGs by partial substitution of Zn or Cu with Al in the baseline Ca-Mg-Zn, Ca-Mg-Cu, and Ca-Mg-Zn-Cu amorphous alloys. Thermal properties of these new metallic glasses, such as the glass transition, crystallization and melting temperatures, as well as heats of crystallization and melting, were determined and the effect of Al on GFA and GS of these alloys was identified.

II.

EXPERIMENTAL PROCEDURES

The master alloys were prepared by induction melting mixtures of pure elements (in atomic percent, 99.99 pct for Al and Cu, 99.9 pct for Mg and Zn, and 99.5 pct for Ca) in a water-cooled copper crucible in an argon atmosphere. Each of the produced alloys was