Microstructural change and precipitation hardening in melt-spun Mg-X-Ca alloys

Abstract

Mg-Al-Si-Ca and Mg-Zn-Ca base alloys were rapidly solidified by melt spinning at the cooling rate of about a million K/s. The melt spun ribbons were aged in the range 100-400 degrees C for 1 h. The effect of additional elements on microstructural change and precipitation hardening after heat treatment was investigated using TEM, XRD and a Vickers microhardness tester. Age hardening occurred after aging at 200 degrees C in the Mg-Al-Si-Ca alloys mainly due to the formation of Al2Ca and Mg2Ca phases, whereas in the Mg-Zn-Ca alloys mostly due to the distribution of Mg2Ca. TEM results revealed that spherical Al2Ca precipitate has the coherent interface with the matrix. Considering the total amount of additional elements, Mg-Zn-Ca alloys showed higher hardness and smaller size of precipitates than Mg-Al-Si-Ca alloys. With the increase of Ca content, the hardness values of the aged ribbons were increased. Among the alloys, Mg-6Zn-5Ca alloy showed the maximum value of age hardening peak(H-v:180) after aging at 200 degrees C for 1 h. (C) 2001 Published by Elsevier Science Ltd.