The Study On Preparation, Micro-structures And Properties Of Mg-Zn-Ca Alloys And Its Composites

Due to the possession of proper elastic modulus and density which is quite similar to natural bone, no-toxic element containing magnesium alloys were regarded as potential bio-degradable materials. However, the majority of those materials could not satisfy the requirement of mechanical and corrosion properties.In this study, we were major in preparing Mg-xZn-1Ca (x =0, 1, 3, 5) alloys and their MMCs which made of HA as reinforcements. Based on the micro-structural analysis, mechanical property and corrosion test, the conclusion can be summarized as following:1. With increasing the content of Zn element, the fraction of intermetallic particles (Ca₂Mg₆Zn₃) in the microstructure of Mg-Zn-Ca alloys gradually increased. Meanwhile, tensile strength and hardness values of those alloys could be enhanced.2. When HA particles were added into Mg-Zn-Ca alloy matrix, some agglomerates were observed in conventional-cast composite. Moreover, the size of agglomerate increased with increasing the percentage of reinforcements. Although the degree of agglomeration could be slightly improved by HPDC process, big size ones still existed in composites. However, HA particles and second phases were effectively distributed by MCAST method, and the micro-structure became homogeneous.3. The addition of Zn, Ca element refined the alloy grain size. HA particles can also significantly reduce the grain size of Mg-xZn-1Ca(x=0, 1, 3, 5)alloys.4. HA particles possessed remarkable effect on the grain size refinement of Al-contained commercial magnesium alloys, especially for AZ91D alloy. Based on the cooling curve measurement, it confirmed that HA particles as effective nucleant site accelerated the process of heterogeneous nucleation.5. For tensile strength properties of HPDC samples, they were improved by addition of HA particles. Meanwhile, the average Vickers'hardness values of Mg-Zn-Ca/HA composites were much higher than corresponding alloys. Furthermore, the average value increased with increasing content of HA inoculants. However, due to the agglomerates of reinforcements in micro-structure, inhomogeneous hardness value for composites could be observed.6. For HPDC samples, the anti-corrosion property in SBF was effectively enhanced by proper addition of HA particles. However, corrosion rate of the sample increased, which resulted from the existence of many structural defects by gradually adding HA inoculants. Compared with HPDC samples, the corrosion properties of counterparts processed by MCAST approach were better.