The effects of Ce addition on the microstructure of Mg-6Zn-1Mn alloy during casting, homogenization, hot extrusion, T4, T6 and T4+two-step aging were investigated. The mechanical properties of alloys with and without Ce were compared. The results showed that Ce had an obvious effect on the microstructure of ZM61-0.5Ce alloy by restricting the occurrence of dynamic recrystallization and restraining the grain growth during extrusion and heat treatment subsequently. A new binary phase Mg₁₂Ce was identified in ZM61-0.5Ce alloy, which distributed at grain boundaries and was broken to small particles distributed at grain boundaries along extrusion direction during extrusion. The mechanical properties of as-extruded ZM61-0.5Ce alloy were improved with the addition of Ce. The improved tensile properties of as-extruded ZM61-0.5Ce alloy were due to the finer grain sizes as compared to ZM61 alloy. However, the UTS and YS decreased severely and the elongation increased when ZM61-0.5Ce was treated by T6 and T4+two-step aging. Brittle Mg₁₂Ce phase, which was distributed at the grain boundary areas and cannot dissolve into the Mg matrix after solution treatment, became crack source under tensile stress.

The effects of Bi addition on the microstructures and mechanical properties of as-cast AZ80 alloy were investigated. The results show that with the addition of Bi, the coarse eutectic phases are refined and become discontinuous; some flaky and granular Mg₃Bi₂ phases with a hexagonal structure of D5₂ are observed along the grain boundaries and between dendrites. The tensile strength and elongation increase first, and then decrease with increasing Bi content. AZ80-0.5%Bi alloy has optimum combination mechanical properties. When the content of Bi is above 1.0% (mass fraction), the amount of flaky Mg₃Bi₂ phase increases markedly, which splits the matrix and deteriorates the tensile strength and elongation.

The effects of inclusions on microstructure, mechanical property, corrosion behavior of Mg-10Gd-3Y (GW103K) alloys by unrefining, MgO ceramic filtering and JDMJ flux refining were investigated, respectively. The results indicate that with decreasing significantly the number and size grade of inclusions for the alloy refined with JDMJ flux, tensile strength and elongation increase; however, the yield strength is less than that of the alloy refined with MgO ceramic filter and unrefined alloy. With the decrease of the inclusions contents, the corrosion rate of the alloys quickly vary from 2.419 mg/(cm²·d) to 1.265 mg/(cm²·d). After inclusion content is reduced to 0.385%, the corrosion rate has almost no changes. Finally, the relationship between the volume fraction of inclusions and service properties of GW103K alloy under different conditions are established quantitatively.

The effects of Sr and Y with different contents on the microstructure and corrosion resistance of AZ31 alloy were investigated. The results indicate that the addition of Sr can obviously reduce the grain size of AZ31 alloy and transform β-Mg₁₇Al₁₂ phase from continuous network to scattered form. Simultaneously, Al₄Sr phase distributed along the boundaries of grains is formed in AZ31-Sr magnesium alloys. The addition of Sr is not as effective as the simultaneous addition of Sr+Y for the refinement of grains, and Al₂Y and Al₃Y phases are distributed both in intracrystalline and along grain boundaries. The corrosion resistance is improved slightly in AZ31 alloy with simultaneous addition of 0.5%Sr+Y. Due to its smallest corrosion current density and corrosion rate, the corrosion resistance of AZ31-0.5%Sr-1.5%Y magnesium alloy is proved the best.

Mg-xGd-0.6Zr (x=2, 4, 6, mass fraction) alloys were prepared by semi-continuous casting process. The effects of Gd content on the microstructures and mechanical properties of Mg-xGd-0.6Zr alloys were studied and the solid solution treatment process of Mg-6Gd-0.6Zr alloys was optimized. The microstructures and mechanical properties of all the studied alloys were analyzed by optical microscope, X-ray diffraction, scanning electron microscope equipped with energy dispersive spectroscope and micro-hardness tester. The results show that the grain size slightly decreases with increasing Gd content and there is a close linear relationship between Gd content and micro-hardness of Mg-xGd-0.6Zr alloys. The second phases Mg₂Gd and Mg₃Gd formed due to non-equilibrium solidification during the casting process can be transformed into equilibrium phase Mg_5.05Gd which can dissolve into α-Mg solid solution phase at solution temperature of 460 °C. The optimized solid solution treatment of Mg-6Gd-0.6Zr alloy is   (300 °C, 6 h) + (460 °C, 10 h).

The effect of aging on the microstructure and mechanical properties of AZ80 and ZK60 wrought magnesium alloys was studied with optical microscope and mechanical testers. The results demonstrate that both the tensile strength and elongation of AZ80 alloy increase firstly and then decrease as the aging temperature rises, the peak values appear when the aging temperature is 170 °C. The hardness of ZK60 alloy increases firstly and then decreases as the aging temperature rises, and the hardness reaches its peak value at 170 °C. However, the toughness of the alloy is just the opposite. Moreover, ZK60 alloy has good performances in both impact toughness and other mechanical properties at the aging temperature from 140 °C to 200 °C.

The microstructural evolution and kinetic characteristics were studied during solution treatment of AM60B Mg alloy prepared by thixoforming. The results indicate that the microstructural evolution includes two stages: the first stage involves rapid dissolution of eutectic β (Mg₁₇Al₁₂) phase, homogenization and coarsening, and the second stage is regarded as normal grain growth consisting of primary α-Mg particles (primary particles) and secondary α-Mg grains (secondary grains). In the first stage, the dissolution completes in a quite short time because the fine β phase can quickly dissolve into the small-sized secondary grains. The homogenization of Al element needs relatively long time. Simultaneously, the microstructure morphology and average grain size obviously change. The first stage sustains approximately 1 h when it is solutionized at 395 °C. Comparatively, the second stage needs very long time and the microstructure evolves quite slowly as a result of low Al content gradient and thus low diffusivity of Al element after the homogenization of the first stage. The growth model of primary particles obeys power function while that of the secondary grains follows the traditional growth equation in the first stage. In the second stage, both of the primary particles and secondary grains behave a same model controlled by diffusion along grain boundaries and through crystal lattice.

The microstructure and mechanical properties of ZK60 Mg alloy were investigated under different solution treatments and artificial aging conditions. When as-cast ZK60 alloy was solution treated at 400 °C for 10 h and artificially aged at 150 °C, the volume fraction of precipitates increased with the aging time up to 30 h. When the as-cast ZK60 alloy was solution treated at 400 °C for 10 h and artificially aged at 200 °C for 15−20 h, the volume fraction of precipitates reached a peak value. Tensile test at room temperature showed that a high density of the second phase precipitates was beneficial to improving the strength and elongation. Solution treatment at 400 °C for 10 h and artificial aging at 150 °C for 30 h is considered the optimum heat treatment condition to obtain a good combination of strength and ductility.

The microstructure and mechanical properties of Mg-10.1Gd-3.74Y-0.25Zr (mass fraction, %) alloy (GW104 alloy) cast by metal mould casting (MMC) and lost foam casting (LFC) were evaluated, respectively. It is revealed that different forming modes do not influence the phase composition of as-cast alloy. In the as-cast specimens, the microstructures are similar and composed of α-Mg solid solution, eutectic compound of α-Mg+Mg₂₄(Gd, Y)₅ and cuboid-shaped Mg₅(Gd, Y) phase; whereas the average grain size of the alloy produced by metal mould casting is smaller than that by lost foam casting. The eutectic compound of the alloy is completely dissolved after solution treatment at 525 °C for 6 h, while the Mg₅(Gd, Y) phase still exists after solution treatment. After peak-ageing, the lost foam cast alloy exhibits the maximum ultimate tensile strength of 285 MPa, and metal mould cast specimen 325 MPa at room temperature, while the tensile yield strengths of them are comparable. It can be concluded that GW104 alloy cast by lost foam casting possesses similar microstructure and evidently lower mechanical strength compared with metal mould cast alloy, due to slow solidification rate and proneness to form shrinkage porosities during lost foam casting process.

Standard mechanical test bars with a diameter of 6.4 mm and a gauge length of 50 mm were processed, and the microstructures of die cast AM60B alloy under different die casting process parameters were observed. The influences of the slow shot speed, the fast shot speed and the biscuit thickness on the externally solidified crystals (ESCs) were investigated. With the increase of the biscuit thickness, the number of the ESCs in the cast samples decreases. Under a low slow shot speed, larg ESCs are found in the cast structure and a high fast shot speed results in more spherical ESCs. The relationships between ESCs and process parameters were also discussed.

The effects of ultrasonic treatment on the microstructure and mechanical properties of Mg-5Zn-2Er alloy at room temperature (RT) and high temperature (HT) were investigated. The microstructure and mechanical properties of the samples were studied by OM, SEM and MTS material tester. The results show that the microstructure and mechanical properties are improved after the ultrasonic vibration. The best effects of ultrasonic vibration on microstructure and mechanical properties were obtained with the ultrasonic vibration power of 600 W and time of 100 s. The cavitation and acoustic streaming caused by ultrasonic treatment play a major role in refining the microstructure and increasing mechanical properties of the alloy.

Mg-14Li-1Al (LA141), LA141-0.3Y, LA141-0.3Sr, and LA141-0.3Y-0.3Sr alloys were prepared in an induction furnace in the argon atmosphere. The microstructures of these alloys were investigated through scanning electron microscope (SEM), X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS). The results show that yttrium and/or strontium additions produce a strong grain refining effect in LA141 alloy. The mean grain sizes of the alloys with addition of Y and/or Sr are reduced remarkably from 600 to 500, 260, 230 μm, respectively. Al₂Y, Al₄Sr and Mg₁₇Sr₂ phases with different morphologies are verified and exist inside the grain or at the grain boundaries, thus possibly act as heterogeneous nucleation sites and pin up grain boundaries, which restrain the grain growth.

The as-cast microstructure and Sr-containing phases in the AZ31 magnesium alloys with different Sr contents (0%, 0.3%, 2.5% and 5.0%, mass fraction) were investigated. The results indicate that after adding Sr to the AZ31 magnesium alloy, the dendrite/grain size is decreased, and with the Sr content increasing from 0 to 5.0%, the dendrite becomes finer, the dendrite morphology becomes more passive and the distribution of alloying phases at dendrite/grain boundary is dispersed. Furthermore, the morphology of the β-Mg₁₇Al₁₂ phase in the alloy with addition of 0.3%Sr changes from continuously irregular strip-like shape to discontinuously irregular strip-like shape and/or fine granule-like shape. At the same time, some lamella-like eutectic phases are found in the alloys with additions of 2.5% Sr and 5.0% Sr, and the lamella spacing in the alloy with addition of 5.0% Sr is finer. Adding high Sr content to the AZ31 alloy can bring the new ternary eutectic and/or divorced eutectic phase of Mg₁₁Al₅Zn₄ in the alloy, and the Mg₁₇Sr₂ and Mg₂Sr phases are formed in the alloys with additions of 2.5% Sr and 5.0% Sr.

The microstructure of WE93 alloy in different states and the mechanical properties at room temperature were investigated, and the creep behavior of the extruded and aged alloy at 200 °C and at stress of 100, 125 and 150 MPa was also discussed. The result shows that the microstructure of as-cast WE93 alloy consists of α-Mg, Mg₁₂(MM) and Mg₂₄Y₅ with an average grain size of 45 μm. After being homogenized at 535 °C for 18 h, the Mg₂₄Y₅ phase is dissolved completely and there is only Mg₁₂(MM) phase left around the grain boundaries. The grains do not grow up as prolonging the homogenization time. The extruded alloy has better mechanical properties than the as-cast alloy, especially the elongation increases to 12.5%. The extruded and aged alloy exhibits the highest yield strength and ultimate tensile strength of 315 and 385 MPa, respectively, however, the elongation decreases to 6.5%. The extruded and aged alloy exhibits good creep resistance at 200 °C and at stress of 100−150 MPa. The creep stress exponent n is 2.97, suggesting that grain boundary sliding plays a dominant role at the corresponding temperature and applied stresses.

The phase constituent evolution of Mg-Zn-Y-Zr alloys with the mole ratio of Y to Zn both in the as-cast and as-annealed states at the Mg-rich corner was investigated by XRD and SEM/EDS analysis and was further explained from the ternary phase diagram calculation. The results show that the formation of the secondary phases in Mg-Zn-Y-Zr alloys firmly depends on the mole ratio of Y to Zn, and X (Mg₁₂YZn)-phase, W (Mg₃Y₂Zn₃)-phase and I (Mg₃YZn₆)-phase come out in sequence as the ratio of Y to Zn decreases. The mole ratios of Y to Zn with the corresponding phase constituent are suggested quantitatively as follows: the phase constituent is α-Mg + I when the mole ratio of Y to Zn is about 0.164; α-Mg + I +W when the mole ratio of Y to Zn is in the range of 0.164−0.33;α-Mg +W when the mole ratio of Y to Zn is about 0.33; α-Mg +W+X when the mole ratio of Y to Zn is in the range of 0.33−1.32; and α-Mg +X when the mole ratio of Y to Zn is about 1.32. The results also offer a guideline for alloy selection and alloy design in Mg-Zn-Y-Zr system.

The microstructure of the 18R-type long period stacking ordered (LPSO) phase in Mg₉₇Y₂Zn₁ alloy was investigated by the first principles calculation. The arrangement rule of Zn and Y atoms in the LPSO structure is determined theoretically. The calculation results reveal that the additive atoms are firstly located in the fault layers at the two ends of the 18R-type LPSO structure, and then extend to fault layers in the interior, which is in good agreement with the experimental observations. This feature also implies the microstructural relationship between 18R and other LPSO structures. The cohesive energy and the formation heat indicate the dependence of the stability of 18R LPSO structure on contents of Y and Zn atoms. The calculated electronic structures reveal the underlying mechanism of microstructure and the stability of 18R LPSO structure.

Sulphur dioxide (SO₂) mixed with carrier gases was used as an alternative to SF₆ to protect molten magnesium alloys. The protection behavior of AZ91D alloy in a sealed melting furnace was investigated under the atmosphere containing SO₂ with different mixed gases. The morphology and composition of the surface film were studied. The melt was well protected in an atmosphere of SO₂ and a proper amount of air, and was not protected properly in the other atmospheres. Based on the understanding of the protective effects of SO₂ in the sealed furnace, the protection mechanism of SO₂-containing cover gases on molten AZ91D alloy was studied in an open melting furnace. The cover gas protected the melt by reacting with the melt to form a coherent protective film with a network structure on the melt surface. The film contains MgO and MgS. MgS increases the Pilling and Bedworth ratio of the surface film and enhances the protective capability of the films.

Magnesium alloys have good biocompatibility, but their mechanical properties and corrosion resistance may not be satisfied for using as degradable materials within bone due to its high corrosion rate in the physiological environment. Nano β-TCP particles were added into Mg-Zn-Zr alloy to improve its microstructure and the properties. As-extruded Mg-3Zn-0.8Zr alloy and Mg-3Zn-0.8Zr/xβ-TCP (x=0.5%, 1.0% and 1.5%) composites were respectively fabricated. The grains of Mg-Zn-Zr/β-TCP composites were significantly refined. The results of the tensile tests indicate that the ultimate tensile strength and the elongation of composites were improved with the addition of β-TCP. The electrochemical test result in simulation body fluid shows that the corrosion resistance of the composites was strongly enhanced comparing with that of the alloy. The corrosion potential of Mg-3Zn0.8-Zr/1.0β-TCP composite is −1.547 V and its corrosion current density is 1.20×10⁻⁶ A/cm².

B₄C_p/Mg-8Li-1Zn and B₄C_p/Mg-8Li-1Al-1Y composites were prepared with hot-extrusion solid-state composite processing. The microstructures and mechanical properties of the composites were studied. With the optimized parameters, the deformation effects and the migration of α phase are improved, and the amount and size of foil gaps are decreased. The bonding force between foils is improved, and the oxidation of foils is lowered. The results of tensile test show that the strengths of the B₄C_p/Mg-8Li-1Zn and B₄C_p/Mg-8Li-1Al-1Y composites are increased obviously after hot-extrusion solid-state composite processing (238 MPa and 257.23 MPa, respectively). The specific strength of B₄C_p/Mg-8Li-1Al-1Y composite is the highest (169.23×10³ cm).

Mg-Li-Gd alloys were prepared by electrochemical codeposition from LiCl-KCl-MgCl₂-Gd₂O₃ melts on molybd, enum electrode with constant current density at 823 and 973 K. The microstructure of the Mg-Li-Gd alloys was analyzed by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The results show that magnesium and gadolinium deposit mainly in the first 30 min, and the alloy obtained contains 96.53% Mg, 0.27% Li and 3.20% Gd (mass fraction). Then, the reduction of lithium ions occurs quickly. The composition of alloy can be adjusted by controlling electrolysis time or Gd₂O₃ concentration in LiCl-KCl melts. With the addition of Gd into Mg-Li alloys, the corrosion resistance of the alloys is enhanced. XRD results suggest that Mg₃Gd and Mg₂Gd can be formed in Mg-Li-Gd alloys. The distribution of Gd element in Mg-Li-Gd alloys indicates that Gd element mainly distributes at the grain boundaries of Mg-Li-Gd alloys.

In order to improve the purifying efficiency of RJ6 flux, 5% (mass fraction) GdCl₃ was introduced into the flux for refining Mg-10Gd-3Y-0.5Zr (GW103K) alloy. The results show that the RJ6 flux containing 5% GdCl₃ exhibits better adsorption ability to nonmetallic inclusions than the one without GdCl₃. Moreover, the mechanical, corrosion properties and fluidity of the alloy refined with RJ6 flux and RJ6 flux containing 5% GdCl₃ were investigated, respectively. It is found that these properties are improved to a certain degree due to the removal of nonmetallic inclusions in the alloy. Thermodynamic analysis and surface tension experiments indicate that the main reason can be ascribed to the decrease of the surface tension of the flux with 5% GdCl₃, which promotes the combination of flux and nonmetallic inclusions.

The effects of Ca and Sr addition on the microstructure and creep properties of Mg-4Al-2Sn alloys were examined. Tensile tests at 25 ˚C and 200 ˚C and creep tests at 150 ˚C and 200 ˚C were carried out to estimate the room temperature and high temperature mechanical properties of these alloys. The microstructure of the Mg-4Al-2Sn alloy showed dendritic α-Mg, Mg₁₇Al₁₂ and Mg₂Sn phases. The latter two phases precipitated along the grain boundaries. The addition of Ca and Sr resulted in the formation of ternary CaMgSn and SrMgSn phases within the grain. The grain size was reduced slightly with the addition of Sr and Ca. The tensile strength was decreased by the addition of Ca and Sr at room temperature. However, the high temperature tensile strength was increased. The creep strength was improved by the addition of Ca and Sr.

The microstructure formation and grains refinement of two Mg-based alloys, i.e. AZ31 and AZ91D, were reported using an electromagnetic vibration (EMV) technique. These two alloys were solidified at various vibration frequencies and the microstructures were observed. The average size of grains was quantitatively measured as a function of vibration frequencies. Moreover, the grain size distribution was outlined versus number fraction. A novel model was proposed to account for the microstructure formation and grain refinement when considering the significant difference of the electrical resistivity properties of the solid and the liquid during EMV processing in the semisolid state. The remarkable difference originates uncoupled movement between the mobile solid and the sluggish liquid, which can activate melt flow. The microstructure evolution can be well explained when the fluid flow intensity versus vibration frequency is taken into account. Moreover, the influence of the static magnetic field on texture formation is also considered, which plays an important role at higher vibration frequencies.

To improve the strength, toughness and heat-resistance of magnesium alloy, the microstructure and mechanical properties of ZA54 alloy reinforced by icosahedral quasicrystal phase (I-phase) particles were studied. Except α-Mg, φ-phase and τ-phase, MgZnYMn I-phase particles can be obtained in ZA54-based composites by the addition of icosahedral quasicrystal-contained Mg-Zn-Y-Mn master alloy. The introduction of MgZnYMn I-phase into ZA54 alloy has great contribution to the refinement of matrix microstructures and the improvement of mechanical properties. When the addition of Mg-based spherical quasicrystal master alloy is up to 3.5% (mass fraction), the macro-hardness of ZA54-based composites is increased to HB 68. The impact toughness of composites reaches the peak value of 18.3 J/cm², which is about 29% higher than that of ZA54 mother alloy. The highest tensile properties at ambient and elevated temperatures with master alloy addition of 2.5% (473 K) are also obtained in ZA54-based composites with 3.5% (mass fraction) Mg-Zn-Y-Mn master alloy addition. The ultimate tensile strength of composites at ambient and elevated temperatures are 192.5 MPa and 174 MPa, which are 23.4% and 33.8% higher than that of ZA54 mother alloy, respectively. The improved mechanical properties are mainly attributed to the pinning effect of I-phase on grain boundaries.

A new shape casting process, melt-conditioned high-pressure die-casting (MC-HPDC) was developed. In this process, liquid metal was conditioned under intensively forced convection provided by melt conditioning with advanced shear technology (MCAST) unit before being transferred to a conventional cold chamber high-pressure die-casting (HPDC) machine for shape casting. The effect of melt conditioning was investigated, which was carried out both above and below the liquidus of the alloy, on the microstructure and properties of a Mg-Al-Ca alloy (AZ91D+2%Ca (mass fraction), named as AZX912). The results show that many coarse externally-solidified crystals (ESCs) can be observed in the centre of conventional HPDC samples, and hot tearing occurs at the inter-dendritic region because of the lack of feeding. With the melting conditioning, the MC-HPDC samples not only have considerably refined size of ESCs but also have significantly reduced cast defects, thus provide superior mechanical properties to conventional HPDC castings. The solidification behaviour of the alloy under different processing routes was also discussed.

The creep behaviors of as-cast Mg-5Zn-2.5Er alloy (mass fraction, %), under various applied stresses (50−70 MPa) and creep temperatures (150−200 ˚C) for 100 h, were investigated. The stress exponent n is in the range of 1.5−5.8, and the activation energy Q_c is in the range of 28.3−77.1 kJ/mol. With respect to the calculated n and Q_c as well as the microstructures after creep, it is suggested that there is a transition region between grain boundary sliding(GBS) dominated creep to dislocation creep mechanism (from n<3 to n>3), arising in the steady-stage creep rate value of 2.89×10⁻⁹ s⁻¹.

The fracture behavior of a permanent mould casting Mg-8.57Gd-3.72Y-0.54Zr (mass fraction, %) (GW94) alloy was investigated under different thermal conditions, including as-cast, solution-treated, peak-aged, and over-aged states. Scanning electron microscopy (SEM) and optical microscopy (OM) were employed to examine the crack nucleation and fracture model. The results indicate that the GW94 alloy shows different behaviors of crack initiation and fracture under different thermal conditions. During tensile test at room temperature, the fracture model of the as-cast GW94 alloy is quasi-cleavage, while that of the solution-treated alloy is transgranular cleavage. It is a mixed pattern of transgranular and intergranular fracture for both the aged conditions. Large cavities formed at grain boundaries are observed in the peak-aged sample tested at 300 ˚C, corresponding to the intergranular fracture. Localized plastic deformation at grain boundaries is also observed and corresponds to the high elongation at 300 ˚C.

Magnesium matrix nanocomposite reinforced with carbon nanotubes (CNTs/AZ91D) was fabricated by mechanical stirring and high intensity ultrasonic dispersion processing. The microstructures and mechanical properties of the nanocomposite were investigated. The results show that CNTs are well dispersed in the matrix and combined with the matrix very well. As compared with AZ91D magnesium alloy matrix, the tensile strength, yield strength and elongation of the 1.5%CNTs/AZ91D nanocomposite are improved by 22%, 21% and 42% respectively in permanent mold casting. The strength and ductility of the nanocomposite are improved simultaneously. The tensile fracture analysis shows that the damage mechanism of nanocomposite is still brittle fracture. But the CNTs can prevent the local crack propagation to some extent.

The sulphur hexa-fluoride gas(SF₆), which is commonly used as the cover gas of molten magnesium alloys in the magnesium industry today, has an extremely high global warming potential(GWP). The protection mechanism of SF₆ containing cover gases on molten magnesium alloys was presented. The cover gas protects the melt by reacting with the melt to form a coherent protective film on the melt surface. The film contains MgO and MgF₂. Particles containing MgF₂ form on the interface between the oxide film and the bulk magnesium alloy, which correspond to the concave areas from the surface observation. These particles increase the Pilling and Bedworth ratio of surface film and enhance the protective capability of the films. Based on the understanding of the mechanism of SF₆, a melting technology in a sealed furnace was proposed, and the protection behavior of magnesium alloys in the sealed melting furnace was investigated under the protective atmosphere containing HFC-134a. The morphology and composition of the surface film were also studied. Experiments to evaluate the protective effect of two other fluorine containing gases with low GWPs on AZ91D alloy in the sealed furnace were also carried out, and the results show that the new gases are potential substitutes for SF₆.

Mg-Gd-Y-Zr alloy was purified by the method of filtering purification. The type, morphology, size distribution and volume fraction of inclusions in the alloy were analyzed using optical microscope and scanning electron microscope, and the effects of the inclusions on the mechanical and corrosion properties of the alloy were investigated. The results indicate that the filtering purification method is effective to remove inclusions in the alloy. By the filtering purification method, the average size of inclusions in the alloy reduces from 12.7 mm to 4.3 mm and the average volume fraction of inclusions in the alloy reduces from 0.26% to 0.06%. The ultimate tensile strength, yield strength and elongation of the alloy are improved from 200 MPa, 156 MPa and 3.4% to 232 MPa, 167 MPa and 7.0%, respectively. The corrosion rate of the alloy decreases dramatically from 38.8g/(m²∙d) to 2.5 g/(m²∙d) in the salt spray test.

The microstructure and mechanical properties of Mg-xCe-0.5Zn (x=0.5, 1.5, 2.5, molar fraction, %) alloys were examined using a nano-indentation technique. The alloys were fabricated using a vacuum induction melting method under an argon atmosphere. The microstructures of Mg-xCe-0.5Zn alloys mainly consist of α-Mg and eutectic Mg₁₂Ce phase. The volume fraction and size of the eutectic Mg₁₂Ce phase increase with increasing Ce contents. Nano-indentation test results show that the indentation hardness and elastic modulus of the eutectic Mg₁₂Ce phase are higher than those of the α-Mg matrix. In addition, the mean indentation hardness and elastic modulus of the Mg-xCe-0.5Zn alloys increase with the Ce addition amount increasing.

A new Mg-14Al-0.5Mn alloy that exhibits a wide solidification range and sufficient fluidity for semi-solid forming was designed. And the microstructure evolution of semi-solid Mg-14Al-0.5Mn alloy during isothermal heat treatment was investigated. The mechanism of the microstructure evolution and the processing conditions for isothermal heat treatment were also discussed. The results show that the microstructures of cast alloys consist of α-Mg, β-Mg₁₇Al₁₂ and a small amount of Al-Mn compounds. After holding at 520  ˚C for 3 min, the phases of β-Mg₁₇Al₁₂ and eutectic mixtures in the Mg-14Al-0.5Mn alloy melt and the microstructures of α-Mg change from developed dendrites to irregular solid particles. With increasing the isothermal time, the amount of liquid increases, and the solid particles grow large and become spherical. When the holding time lasts for 20 min or even longer, the solid and liquid phases achieve a state of dynamic equilibrium.