Effect Of High Ca On Microstructure And Mechanical Property Of Mg-Zn-Nd Alloy

The Mg-13Zn-x Ca-0.5Nd(x=3,4,5,6)as-cast alloys and Mg-5Zn-x Ca-Nd(x=0,1,2,3)as-extruded alloys containing high-calcium have been prepared under the pretension of a mix gas atmosphere of Ar, using optical microscope, SEM,EDS, XRD, hardometer and tensile testing machine to analyze the variations of microstructure and mechanical property. The main works are as follows:1.As-cast Mg-13Zn-x Ca-0.5Nd(x=3,4,5,6) alloys(1)If the addition amount of calcium, Eutectic structure(a-Mg+ Mg6Zn3Ca2 and a-Mg+Mg6Zn3Ca2+Mg2Ca)and Mg2 Ca main second phase near the grain boundaries. With the increasing of Ca, the structure is fined. However eutectic structure solid solved in the matrix at 390? for 8h solid solution. And then at aging 240? for 8h.,it promote second phase precipitation and dispersive distribution. It can improve mechanical properties greatly. After T6 heat treatment, the strengthening mechanism is considered as fine grain strengthening and second phase strengthening. In order to improve mechanical properties especially, the Mg-13Zn-4Ca-Nd alloys has good foreground with the characteristics of high hardness and good mechanical properties.(2)It is calculated the nucleation ability force of different elements in magnesium alloys by using the GRF model. It is found that with the increase of Ca addition, the value of GRF was increase. On one hand, base on good suspensions of Ca,it can increase the constitutionally supercooling region and restraining the dendrite growth. On the other hand, Ca supplies the thermodynamic driving force for the nucleation and increases the number of effective nucleation particles.2. As-extruded Mg-5Zn-x Ca-Nd(x=0,1,2,3)alloys(1)It is found that the dynamic recrystallization occurs during the process of hot extrusion. The alloys are mainly composed of the fine equiaxial grains. With the Ca content increased, it could improve the stability of the second phase and refine the grains. The high content of Ca has a high value of hardness.(2)After aging for 48 h at 200 ?, the alloys obtain the peak hardness and the peak hardness values of the alloys are 60 HV, 63 HV and 66 HV, respectively. When the content of Ca increases to 3.0wt.%, the alloy exhibits the best age-hardening behavior. The strength of the extruded alloy is enhanced with the increase of Ca content. After the aging treatment, the tensile strength of the alloys are ulterior improved, but the elongation decreases.