Study on Rapidly Solidified Powder Magnesium Alloys

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Rapidly solidified P/M materials were produced for AZ91 and ZK61 magnesium alloys with alloying additions of Si, Ni, Mn and Ce, and their mechanical properties were examined, with the prupose of improving properties of conventionally processed magnesium materials. Rapidly solidified flakes showed cellular dendritic structures of 1 to 2 mum in the average cell size. The cooling rate during solidification was estimated as 10^4 to 10^5 K/s. P/M materials of 7 mm in diameter were produced by cold pressing and hot extrusion.Among obtained P/M materials of AZ91 based alloys, Si bearing alloy showed the highest peak hardness when aged at 433 K. Ni and Ce bearing alloys showed very little age hardening for both AZ91 and ZK61 based alloys. Mn bearing ZK61 alloy showed higher age hardening at 403 K than the base alloy. Rapid solidification of magnesium alloys with some proper alloying additions was shown to be very effective in increasing strength of magnesium alloys. Among the all tested materials, P/M materials of Ce added ZK61 alloy showed the highest tensile strength of 554 MPa. The specific strength of this alloy was as high as 295 MPa and exceeded those of 7075 aluminum alloy and Ti-6Al-4V. At elevated temperatures, rapidly solidified P/M materials showed lower tensile strength and higher elongation than I/M magnesium materials. P/M materials of AZ91 alloy showed elongation higher than 400% at 573 K, which is in the superplastic deformation regime. Thus, the salient features of rapidly solidified magnesium P/M materials are higher strength at room tempearture and higher ductility at elevated temperatures than the conventionally processed magnesium materials.