Effect of Yttrium on Morphologies of Precipitation Phases Along Grain Boundary of As-cast ZK60 Magnesium Alloy

Morphologies of precipitation phases along grain boundary of the as-cast Mg-6.0Zn-0.45Zr, Mg-6.0Zn-(1.2Y) and Mg-6.0Zn-0.6Zr-1.0Y alloys are studied by using the methodologies of metallurgical phase analysis, scanning electron microscopy(SEM) analysis and energy diffraction x-ray(EDX) analysis. The experimental result indicates that the main precipitation phases along grain boundary of the as-cast alloys Mg-6.0Zn-0.45Zr is Mg-Zn binary phase. There are two kinds of precipitation phases along grain boundary for Mg-6.0Zn-1.2Y and Mg-6.0Zn-(0.6)Zr-1.0Y alloys. One grew at triangular grain boundary, which is fish-bone -like and contained Mg-Zn binary phase and Mg-Zn-Y ternary phase. The other distributed mainly around the grain, which is net-like and contained Mg-Zn-Y ternary phase. In addition, there are lots of granular phases, extending to the interior of the grain, at the rim of grain boundary phases. Finally, Y can intensively change morphology of precipitation phases along grain boundary of the as-cast Mg-Zn-Zr alloy (ZK60) alloys.     

Effect of Mischmetal Additions on the Ignition Temperature ofMolten ZM5 Magnesium Alloy

Magnesium alloy is prone to burning during its melting and casting in air, which is a major factor in obstructing its application. Fluxes and cover gases are currently used for the melting and production processes, and semi solid thixocasting is also used to lower the operation temperature, but there still remain many problems. Alloying is a promising method of preventing Mg from burning. The effect of mischmetal additions on the ignition temperature of ZM5 Mg alloy was investigated and compared with that of pure rare earths. It is shown that an addition of 0.12 % mischmetal can greatly heighten the ignition point and such an alloy can be widely applied.     

Research Status and Development of AZ31 Magnesium Alloy

The characters of AZ31 Magnesium Alloy are reviewed. The effects of main alloying elements on microstructures and properties, mechanical properties, grain refinement and superplasticity of AZ31 magnesium alloy are discussed. Future development directions and application areas are also introduced, noting that new forming technology magnesiumbased composites and the basis theory of AZ31 Magnesium Alloy should be future research emphases.     

Cyclic Creep Constitutive Model of Magnesium Alloy at High Temperature

With high strength-to-weight ratio and excellent technological properties, Magnesium Alloy plays a more and more important role in automotive industry. But the inferior high temperature creep resistance limited its application to power components such as engine and transmission cases. In order to investigate the cyclic creep behavior of Magnesium Alloy at high temperature, creep tests of plate specimens AM50 were conducted. Through the analysis about the microstructure and defects of AM50, an isotropic and scalar damage parameter was introduced into an existing creep constitutive model. Furthermore, a Fortran code based on numerical algorithm was developed to simulate plasticity, cyclic creep, and recovery phenomenon observed. Comparisons between calculated results and experimental data show good agreement.     

Damage Constitutive Relationship of Coupled Plasticity-creep for Magnesium Alloy

Based on a simple mechanical model and an appropriate definition of generalized time,a constitutive equation is obtained for coupled plasticity and creep behavior of materials.A damage evolution based on a spherical void model for mixed hardening materials is obtained by means of Gurson's model.The damage evolution law is embedded in the adopted constitutive equation,and a damage constitutive equation is obtained for coupled plasticity and creep behavior of die-casting magnesium alloy.The response of magnesium alloy subjected to cyclic loads is analyzed.The validity of the proposed model is demonstrated by the satisfactory agreement between the experimental and calculated results.     

Numerical Simulation of Eelastoplastic Multi-scales Model for Casting Magnesium Alloy

To realize the transforms of stress and strain and obtain the multi-scale constitutive equation across micro/meso/macro scales.strain-stress curves for magnesium alloy(AM60) and magnesium matrix are carried out with the machine MTS.By means of mixture law,mechanical property of particle is obtained.Based on the character of magnesium alloy structure,the finite element model of unit-cell included complex micro-structures is carried out.Via finite element numerical simulation of magnesium alloy unit-cell,the methodology overcome the limitation of present analytical method.Finally the multi-scale constitutive equation has been used for the analysis of the tensile stress vs. strain curve for magnesium alloy.Results show satisfactory agreement between the stress vs strain curve by the present methodology and the experimental data for AM60.     

Formation Model of Alumina in the Course of Directed Oxidation of Aluminum Magnesium Alloy

By analyzing the characteristics of magnesium volatilization and linear growth kinetic of Al/ Al_2O_(3 )in directed oxidation of Al-Mg alloy, as the formation process of MgO is considered to be the process of which Al_2O_(3)dissolved in the scale MgO and MgO is partially n-type oxide, formation condition of Al_2O_(3)is established easily in the coure of oxidation. Volatilization of magnesium is to promote the growth of p-type MgO in the surface layer and the formation of Al_2O_(3 )in the inner layer of n-type MgO, and to promote the transformation of MgO toMgAl_2O_(4).MgAl_2O_(4)plays an important role in the formation process of Al_2O_(3), growth stress between MgO and MgAl_2O_(4)cause the formation of cavity in the MgAl_2O_(4 )and aluminum alloy melts is easier to transfer to oxidation front by means of this cavity. The transformation velocity ofMgO to MgAl_2O_(4 )depends on growth kinetic of Al_2O_(3),the faster transformation velocity of MgO to MgAl_2O_(4)is main reason that growth kinetic of Al/Al_2O_(3)transformation exhibits linear relationship.     

Numerical Simulation of Elastoplastic Multi-scales Model for Magnesium Alloy Under Tensile Load

In order to investigate the macroscopical mechanical performance of magnesium alloy material containing pore and the mechanism during distorting destructing, an accurate finite element model of magnesium alloy using the multiscales method was developed, and the macroscopic properties of material under the macroscopic tensile load using the developed constitutive model of multi-scales and finite element method was obtained. By analyzing the distortion results of meso-model through the multi-scales method, with macroscopical load increasing, the difference demonstrated on the macroscopic is very small, however, with the increase of the load step, the phenomenon that the ability of plasticity deformation of the meso-models which includes the cuboid pore decreased gradually remarkable and the phenomenon of stress centralized is more severity than the meso-models including cylindrical pore could be obviously observed during the process of deformation on the meso-models.     

Influences of Y on the microstructures and mechanical properties of Mg-12Gd-1Zn-0.6Zr magnesium alloys

To develop Mg-Gd-Y based high-strength alloys and widen the application of magnesium alloys, the effects of Y addition on the microstructure and mechanical properties of Mg-12Gd-1Zn-0.6Zr alloy are investigated by using both optical and electron microscopy,X-ray diffraction (XRD),differential scanning calorimetric (DSC) analysis,and tensile test．The results indicate that adding 2%Y to the Mg-12Gd-1Zn-0.6Zr alloy does not cause an obvious change in the as-cast microstructure of the alloy. However,after adding 3%and 4%Y,the as-cast microstructure of the alloy is coarsened,and simultaneously the morphology of the secondary phases in the alloy is changed from the initial discontinuous fine network to thick skeleton-like frame. Furthermore,adding 2%-4%Y to the Mg-12Gd-1Zn-0.6Zr alloy can also refine the grains of the as-extruded alloy,and adding 2%and 3%Y can obtain higher refining efficiency than adding 4%Y. In addition,adding 2%-4%Y to the Mg-12Gd-1Zn-0.6Zr alloy can also effectively improve the ultimate tensile strength and yield strength of the as-extruded alloy,and the ultimate tensile strength,yield strength and elongation of the as-extruded alloy with the addition of 2%Y can reach 348.8 MPa,256.8 MPa and 14.7%,respectively.     

Calculation of Properties of Fracture for Magnesium Alloy AM50 and Experimental Certification

The strain-stress curve and the stress intensity factor are carried out using the machine MTS for Magnesium alloy AM50.Energy release rates(G)are evaluated based on the virtual crack closure technique and Griffith potential energy.Based on the relationship between Energy release rate(G)and stress intensity factor(K).And then stress intensity factor(K) is got.Comparison of stress intensity factors(K) of between the calculated values and experimental values is made,showing that they are in good agreement.     

施用农用氢氧化镁对白菜、晚稻产量及土壤镁素的影响

闽清县耕地土壤有78.3%属缺镁水平。为探索施镁肥对农作物增产效果,以农用氢氧化镁为供试肥料,选用本地区种植面积较大、对镁元素敏感的白菜、晚稻两作物进行田间试验,分别按镁肥用量不同设5个水平,氢氧化镁肥全部采用全层基施。结果表明,施用镁肥均不同程度提高了水稻分蘖期与齐穗期叶绿素含量。适宜用量范围内,施用氢氧化镁均提高了白菜、晚稻产量,其中白菜、晚稻分别以氢氧化镁用量225、120kg/hm²增产效果最佳,分别增幅12.7%与9.1%,经济效益分别增效12423.9、1410元/hm²。但晚稻用量超过120kg/hm²,产量显著下降。在最高产量下的施镁肥水平,与CK相比,种植白菜与晚稻田块土壤有效镁分别增加14.3与11.3mg/kg。在土壤有效镁基本相当条件下,晚稻对镁肥较白菜表现敏感,过多反而减产。总之,闽清县在白菜与晚稻上施用氢氧化镁,既增产增收又能提高土壤有效镁的含量,促进耕地养分平衡,但需掌握合理用量。     

Phase Transformation Diffusion Bonding of Titanium Alloy to Stainless Steel

Jointing of titanium alloy and stainless steel is very often in the fields like aviation, chemical plants etc. The combination of materials has the advantages of both titanium alloy and stainless steel and will reduce the consumption of titanium resource. The phase transformation diffusion bonding of TA17 titanium alloy to 0CriSNigTi stainless steel are carried out on Gleeble - 1500D. The effcet of maximum thermal cycle temperature, the tensile strength, the fracture surface and microstruture of the joints are investigated. The results show that TiFe and TiFe2 intermetallics and some solid solutions are formed along the interface, when maximum thermal cycle temperature increase, the area proportion of intermetallics in the fracture surface increase, which are detrimental to the mechanical properties of the transition joints.