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MICROSTRUCTURE AND MECHANICAL PROPERTIES OF TWIN-ROLL STRIP CAST  MAGNESIUM ALLOYSG.

T. Bae, S. S. Park and N. J. Kim
Center for Advanced Aerospace Materials, POSTECH, San 31,Hyjadong, Namgu,
Pohang, 790-784 , Korea (email: njkim@postech.ac.kr)

Mg alloys are the lightest commercial structural alloys and normally show a very good castability and machinability as well as excellent specific strength and stiffness. However, due to the low workability of Mg, there is a lack of competitive Mg wrought products, especially sheet materials, which are much needed for numerous weight-sensitive applications. Recent development of twin-roll strip casting technology has shown that it can efficiently produce low cost, high performance Mg sheet products having equivalent mechanical properties to conventional ingot cast Mg alloys. Twin-roll strip casting has beneficial effects on microstructure such as reducing segregation and grain size. Since twin-roll strip casting offers a relatively high solidification rate, it can incorporate alloying elements which have limited solid solubilities without forming coarse deleterious intermetallic particles.

In the present study, several Mg alloys were subjected to twin-roll strip casting and their microstructure and mechanical properties were evaluated. Alloying elements were chosen to incorporate various types of second phase particles. Types of second phase particles include precipitates, primary dispersoids as well as quasicrystalline particles. Twin-roll strip cast alloys were subjected to thermo-mechanical treatment for modification of microstructure. It shows that microstructure after thermo-mechanical treatment is quite dependent on the alloy composition, more precisely the type of second phase particles. The alloys having fine primary dispersoid particles show the finest grain size after thermo-mechanical treatment. Effects of alloying elements and thermomechanical treatment on the microstructure and mechanical properties were analyzed with emphasis on the formation of second phase particles.