Effects of Mn Addition on the Microstructure and Mechanical Properties of As-cast and Heat-Treated Mg-Zn-Ca Bio-magnesium Alloy

Abstract

The effects of manganese (Mn) addition on the microstructure, tensile properties and hardness of the as-cast (AC) and heat-treated (HT) Mg-2Zn-0.5Ca-xMn (x = 0.5, 1.0 and 1.5 wt%) alloys were investigated for biomedical osteosynthesis applications. The transformation of the microstructure and precipitation of the AC and HT alloys with different Mn additions were analyzed by optical microscope, x-ray diffraction, scanning electron microscope and transmission electron microscope. Mechanical properties of the alloys were tested on an electronic universal testing machine and a micro-hardness tester. The results showed that the polygonal α-Mn precipitate was the existing form of Mn in the alloys, which was attached by Mg-Zn phases. With increasing the Mn addition, the grains in the AC Mg-2Zn-0.5Ca-xMn alloys became more refined, and changed from bulky and uneven dendrite crystal to uniform equiaxed crystal. Meanwhile, the MgZn2 and Mg2Zn3 phases increased in HT alloys with the increase in Mn addition. Moreover, the strength and elongation of the AC and HT alloys both decreased after reaching a peak with the increase in Mn addition. The HT Mg-2Zn-0.5Ca-1.0Mn alloy also possessed the optimal tensile strength of 205 MPa and the elongation of 15.7% among the alloys in this study.