热挤压铸造新型镁合金微观组织及细胞生物活性分析

采用热挤压铸造工艺制造新型镁合金, Mg-Nd-Zn-Zr-Mn (平衡-3-0.2-0.4-0.2%)基, 研究了新型镁合金表面特征、力学性能及细胞生物活性. 选择NZ30K添加Mn元素制成新镁合金, 挤压前通过均匀化热处理, 减少挤压过程中铸态合金中的粗大析出相以及树枝晶形成的带状组织. 光谱测试分析合金成分; 显微观察合金铸态、横纵截面; 扫描电镜扫描; X射线衍射分析. 将合金制成金属棒、螺钉、接骨板等形状, 测试力学性能. 进行体外细胞培养, 利用DMEM完全培养基制作镁合金浸提液, 滤膜过滤后4℃保存; 大鼠骨髓间充质干细胞提取培养, 待细胞生长至70%~80%传代于24孔板种板, 添加浸提液培养12、24、36h, 利用线粒体膜电位检测试剂盒检测细胞凋亡活性. 以纯镁作为对照组, 进行力学性能测试及细胞活性凋亡测试. 热挤压后合金的组织由细小的再结晶晶粒与变形晶粒组成, 与铸态合金相比, 其组织明显细化. 经挤压加工后, Mg-3Nd-0.2Zn-0.4Zr-0.2Mn合金横截面为细小的等轴晶组织, 组织均匀性好; 纵截面出现了晶粒尺寸相对较大的长条状组织, 组织均匀性稍差. 扫描电镜图显示Mg-3Nd-0.2Zn-0.4Zr-0.2Mn合金中第二相颗粒沿挤压方向被碾碎成更细小的颗粒, 只有非常少量的弥散分布的颗粒状析出相, 而在该合金中有较多被碾碎的第二相, 发生了明显的动态再结晶, 挤压后获得的组织不均匀, 大晶粒被发生再结晶的小晶粒包围. 从X射线衍射图中可以看出该合金铸态组织主要由α-Mg、Mn、Mg12Nd和Y相等这几相组成. 力学性能测试表明, 新型镁合金综合力学性能明显优于纯镁金属. 短期细胞培养中, 新型镁合金无明显细胞毒性, 对细胞生长有积极促进作用. 新型镁合金热挤压后的横截面为细小等轴晶组织, 组织明显细化且均匀性好, 力学性能有极大提升; 在短期细胞培养过程中新型镁合金与纯镁都表现出无细胞毒性, 新型镁合金对细胞活性的提升优于纯镁组.

Analysis on microstructure and cell biological activity of new magnesium alloy by hot squeeze casting

A new magnesium alloy, Mg-Nd-Zn-Zr-Mn (equilibrium-3-0.2-0.4-0.2%) base, was fabricated by hot squeeze casting. Its surface characteristics, mechanical properties and cell biological activity were studied. NZ30K was selected to add Mn element to make the new magnesium alloy, and homogenization heat treatment was carried out before extrusion to reduce both the coarse precipitated phase and the banded structure formed by dendrites in the as-cast alloy during extrusion. Spectroscopic analysis of alloy composition was carried out. The as-cast, transverse and longitudinal sections of the alloy were observed microscopically. The alloy was also analyzed by scanning electron microscope (SEM) and X-ray diffraction. The alloy was made into metal rod, screw, bone plate and other shapes to test the mechanical properties. In vitro cell culture, magnesium alloy extract were prepared using DMEM complete medium, and stored at 4℃ after filtration. Rat bone marrow mesenchymal stem cells were extracted and cultured to 70% to 80% and then subcultured in 24-well seed plates. The cells were cultured with extractions for 12, 24 and 36 hours. The apoptosis of the cells was detected by mitochondrial membrane potential detection kit. Pure magnesium was used as control group to test mechanical properties and apoptosis of cells. The microstructure of the alloy after hot extrusion was composed of fine recrystallized grains and deformed grains. Compared with the as-cast alloy, the microstructure of the alloy after hot extrusion was refined obviously. After extrusion, the cross section of Mg-3Nd-0.2Zn-0.4Zr-0.2Mn alloy was fine equiaxed grain with good uniformity. Long strip structures with relatively large grain size appeared in the longitudinal section, and the microstructure uniformity was slightly less. The SEM figure showed that the second phase particles in Mg-3Nd-0.2Zn-0.4Zr-0.2Mn alloy were crushed into finer particles along the extrusion direction, with only a very small amount of dispersed granular precipitates. However, there were more crushed second phases in Mg-3Nd-0.2Zn-0.4Zr-0.2Mn alloy, and obvious dynamic recrystallization occurred. The microstructure obtained after extrusion was not uniform. Large grains were surrounded by small grains that underwent recrystallization. The as-cast microstructure of the alloy was mainly composed of α-Mg, Mn, Mg12Nd and Y phases. The comprehensive mechanical properties of the new magnesium alloy were better than those of pure magnesium alloy. In the short-term cell culture, the new magnesium alloy had no obvious cytotoxicity, and had positive promoting effect on cell growth. The cross section of the new magnesium alloy after hot extrusion was fine equiaxed crystal structure with good uniformity, and the mechanical properties were greatly improved. In the short-term cell culture process, both the new magnesium alloy and pure magnesium showed no cytotoxicity, and the new magnesium alloy improved the cell activity better than the pure magnesium group.