Microstructures and Mechanical Properties of Direct-Extruded Novel Mg Alloys. (2017)

• Record Type: Journal Article
• Authors: Suh, Joung Sik; Klaumünzer, David; Kim, Ha Sik; Kim, Young Min; You, Bong Sun
• Is Part Of: Procedia engineering. Volume 207(2017)
• Page Start: 908
• Page End: 913
• Publication Date: 2017
• Subjects: Magnesium alloy -- Extrusion -- Microstructure -- Mechanical properties -- Work hardening; Engineering -- Congresses; Engineering -- Periodicals; Engineering; Conference proceedings; Periodicals; 620.005
• DOI: 10.1016/j.proeng.2017.10.850
• Languages: English
• ISSNs: 1877-7058

Abstract

Abstract: Non-flammability and high production rate are prerequisite for extending application of Mg extrusion products. In this respect, the present study focuses on microstructure development and mechanical behavior of two novel Mg alloys as compared with a commercial Mg alloy. As a reference, Mg-8Al-0.4Zn (AZ80 bal. wt.%) is extrudable at low speed of 0.5-2.5 m/min. This is due to hot shortness during extrusion, which results from low melting point of secondary phases like Mg17 Al12 . Furthermore, Mg alloys are reactive in molten state and rapidly ignited as contacting with oxygen in air. Hence, a non-flammable Mg alloy was developed by a trace addition of 0.3%Ca and 0.2%Y, which form protective oxide layer on Mg grains (AZ80+0.3%Ca+0.2%Y denoted as SEN8). In other way, Mg-5Sn-4Al-1Zn (TAZ541) was developed for high-speed extrusion. Hereby Mg2 Sn precipitate makes Mg matrix thermally stable due to its high melting point. Three Mg alloys were extruded in the form of 50 mm x 4 mm plate with extrusion ratio of 25:1 at 350 °C with 1.1 m/min. As-extruded microstructures exhibited fully recrystallized structure with equiaxed grains as well as partially elongated grains along the extrusion direction. There was no big difference in grain size with 17.7~19.6 µm. SEN8 showed the weakest texture owing to the effect of Ca and Y. This made yield strength of SEN8 lower and uniform strain higher than AZ80. Mg2 Sn particles led to higher work hardening of TAZ541 than AZ80 and SEN8. Moreover, SEN8 and TAZ541 had higher hardening capacity due to lower yield strength and higher work hardening rate than AZ80. That is, their relatively weak textures resulted in superior hardening ability. This presented that texture has a more dominant effect on mechanical properties rather than grain size in extruded Mg alloys. Regarding the effects of Ca, Y and Sn, it enables development of next generation Mg alloys with high strength and non-flammability for high-speed extrusion.