Abstract

Various kinds of Mg-Zn-Ca base alloys were rapidly quenched via melt spinning process. The meltspun ternary and quaternary alloy ribbons were heat-treated, and then the effects of additional elements on age hardening behavior and phase change of precipitates were investigated using Vickers hardness tester, XRD, and TEM equipped with EDS system. In ternary alloys, age hardening was mostly due to the distribution of Mg_6Ca_2Zn_3 and Mg_2Ca. The stable phases of precipitates were varied according to the aging temperature and the alloy composition. With the increase of Ca content, Mg_2Ca precipitates were detected more than Mg_6Ca_2Zn_3 precipitates. In quaternary alloys, the precipitates taken from Mg-Zn-Ca-Co were identified as new quaternary phase, whereas those taken from Mg-Zn-Ca-Zr as MgZnCa containing Zr. In general, the ternary alloy showed higher peak hardness and thermal stability than the quaternary considering the total amounts of the solutes. It implies that the structure of precipitate should be controlled to have the coherent interface with the Mg matrix.

• Keywords: Mg alloy;Melt spinning;Precipitate;Age hardening;Microstructure;