ICP-AES Determination of Germanium in GdSiGe Series Alloys as Magnetic Refrigeration Material

The ICP-AES method for the determination of Ge in GdSiGe series alloys was studied.As the three main elements in the alloys,Gd,Si,and Ge differ greatly from each other in chemical properties,it was difficult to pretreat the sample.Two decomposition methods were compared,and a mixture of HNO3＋HF was used to decompose the sample and the effect of the HF amount on the sample decomposition was examined.The adsorption effect of GdF3 on Ge was discussed.Three GdSiGe series alloy samples were analyzed,and the RSDs of this method were in the range of 0.85%～2.66%.

Influence of Al content on machinability of AZ series Mg alloys

Influence of A1 content on the machinability of AZ series cast Mg alloys was investigated. In order to evaluate the machinability of the alloys, measurements of the cutting forces during turning operations and surface roughness were carried out as well as considering the microstructure and tensile properties. The results show that maximum tensile properties are observed with 2% （mass fraction） A1 addition to Mg. As the A1 content of the alloy increases above 2%, the cutting forces tend to reduce along with the ductility owing to the grain boundary precipitation of intermetallic phase （fl-Mgl7All2）. Cutting forces are able to increase as the cutting speed increases for all the alloys studied, and it＇s attributed to flank built up at the tip of the cutting tool during machining.

Strengthening-toughening of 7xxx series high strength aluminum alloys by heat treatment

The effects of stepped solution heat treatments on the dissolution of soluble remnant constituents and mechanical properties of 7055 aluminum alloy were investigated. It was shown that a suitable pretreatment at lower temperature can enable complete dissolution of the constituent particles in 7055 alloy without overheating by subsequent high temperature solution treatment. This in turn increased the tensile strength and fracture toughness of 7055 alloy to 805 MPa and 41.5 MPa·m 1/2 respectively, with approximately 9% tensile elongation. The near solvus pre precipitation following after high temperature solution treatment was also studied on 7055 aluminum alloy. The effect of the pre precipitation on the microstructure, age hardening and stress corrosion cracking of 7055 alloy was investigated. The optical and transimission electron microscopy observation show that the near solvus pre precipitation can be limited to grain boundary and enhance the discontinuity of grain boundary precipitates in the subsequent ageing. The stress corrosion cracking resistance of aged 7055 alloy can be improved via the pre precipitation with non deteriorated strength and plasticity.

Influence of aluminum content on machinability of AS series cast magnesium alloys

The influence of Al content on machinability of AS series cast Mg alloys was studied. The assessment of machinability of Mg alloys was performed by measuring the cutting forces and surface roughness. The microstructure and the tensile properties were also studied. The results reveal that cutting forces are increased with the increase of the Al content. Surface roughness and mechanical properties are the highest for AS91 Mg alloy. It is assumed that the main mechanism, which has an influence on the mechanical properties, is the presence of intermetallic phases(Mg2Si and Mg17Al12). Cutting forces increase with the increase of the cutting speed in machining of all Mg alloys. These measured data are in accordance with the mechanical properties of the machined alloys.

Grain refinement of Mg-Al alloys inoculated by MgAl_(2)O_(4)powder

As a potent nucleating substrate forα-Mg grain,MgAl_(2)O_(4) powder was used to inoculate the Mg-Al melt in this study.The effects of MgAl_(2)O_(4)amount,holding time and Al content on the grain size and grain refining ratio of the inoculated Mg-Al alloys are systematically investigated.The results show that the minimum grain size of Mg-3Al alloy is achieved by adding 2wt.%MgAl_(2)O_(4)powder and this alloy exhibits higher grain refining ratio than Mg-5Al and Mg-8Al alloys.The crystallographic misfit calculation indicates the wellmatching and possible orientation relationships(ORs)betweenα-Mg and MgAl_(2)O_(4).Among these predicted ORs,[10–10]α−Mg//[110]MgAl2O4 in(0002)α−Mg//(1–13)MgAl2O4 possesses the smallest misfit,i.e.,2.34%(fr).Both results of the experiment and crystallographic calculation demonstrate that the grain refinement of Mg-Al alloys is attributed to the MgAl_(2)O_(4)particles acting as the heterogeneous nucleation substrates forα-Mg grains.

Effect of Rare Earths on Hot Cracking Resistant Property of Mg-Al Alloys

The effect of rare earths （RE） ranging from 0.1% to 1.2%（mass fraction） on hot cracking resistant property of Mg-Al alloys was investigated. The results show that hot cracking resistant property of Mg-Al alloys remarkably declines with an increase of RE addition. The causes of the decline are as follows： First, grain coarsening of Mg-Al alloys caused by RE addition reduces the fracture strain required for hot crack initiation. Second, RE reduces the eutectic microstructure of Mg- Al alloys, and as a result, shortens the time that the feeding channel remains open, making it difficult to feed the alloy. Furthermore, RE elevates the eutectic reaction temperature, which leads to the decrease in the strength of the interdendritic liquid film at the late stage of solidification. Third, when a-Mg dendrites form continuous skeletons, the interdendritic Al11 RE3 phase tends to block the feeding channels and increases the difficulty of feeding. Last, the shrinkage ratio discrepancy between Al11RE3 phases and α-Mg matrix is prone to cause shrinkage stress and promote hot crack initiation.

A comparative study on corrosion of Mg-Al-Si alloys

Corrosion behavior of various Mg-Al-Si alloys(AS11,AS21,AS41,AS61and AS91series),cast under the same coolingconditions and controlled alloying composition,was investigated systematically.Optical microscopy and scanning electronmicroscopy were used for microstructural examinations.The corrosion behavior was evaluated by immersion tests andpotentiodynamic polarization measurements in3.5%NaCl solution.The results from both immersion tests and the potentiodynamicpolarization measurements showed that marginal improvement in corrosion resistance was observed with2.0%Al(mass fraction)containing alloy(AS21)whereas Al addition above2.0%(AS41,AS61and AS91)deteriorated the corrosion resistance which wasattributed toβphase,acting as cathode,and the interruption of continuity of the oxide film on the surface of the alloys owing tocoarsenedβand Mg2Si phases.

Grain Coarsening Behavior of Mg-Al Alloys with Mischmetal Addition

Small addition of mischmetal （MM） into aluminum alloys can lead to grain refinement. However, it is still uncertain whether the same effect applies to Mg-Al alloys. This work indicated that small amount of mischmetal addition ranging from 0.1% to 1.2% （mass fraction） did not cause grain refinement in Mg-Al alloys. On the contrary, they tended to coarsen the grains. When added into Mg-Al alloys, MM reacted preferentially with Al to form Al11 MM3 phase. As Al11 MM3 phase mainly distributed within α-Mg grains than at grain boundaries, it had little effect in restricting grain growth. In addition, MM reacted with Al8（Mn, Fe）5 or ε-AlMn particles to form Al-MM-Mn compounds, thus it reduced the amount of heterogeneous nuclei in the melt and resulted in remarkable grain coarsening.

Microstructure analyses and phase-field simulation of partially divorced eutectic solidification in hypoeutectic Mg-Al Alloys

In this study the partially divorced eutectic microstructure ofα-Mg andβ-Mg17Al12was investigated by electron backscatter diffraction,transmission electron microscopy,and phase-field modeling in hypoeutectic Mg-Al alloys.The orientation relationships between the individual eutecticαgrains,eutecticβphase,and primaryαgrains were investigated.While the amount of eutectic morphology is primarily determined by the Al content,the in-depth microstructure analyses and the phase-field simulation suggest non-interactive nucleation and growth of eutecticαphase in theβphase grown on the interdendritic primaryαdendrites.Also,phase-field simulations showed a preferred nucleation sequence where theβphase nucleates first and subsequently triggers the nucleation of eutecticαphase at the movingβphase solidification front,which supports the microstructural analysis results.

Combustion synthesis of fine TiFe series alloy powder by magnesothermic reduction of ilmenite

Fine TiFe series alloy powder was fabricated by magnesothermic reduction of ilmenite as main raw material.Adiabatic temperature of the FeTiO_(3)-Mg system was studied through thermodynamic analysis.Meanwhile,the characteristics of TiFe series alloy were described by XRD,SEM and grading analysis.It is shown that combustion synthesis of the FeTiO_(3)-Mg system can carry out due to its strong exothermic reaction through adiabatic temperature calculate.Ultrafine TiFe series alloy powder after leached for 5 h has reasonable phases and morphology with the particle distribution of 0.2 to 1μm.It indicates that in-situ magnesothermic reduction of natural ilmenite is a feasible way to fabricate ultrafine powder with a relatively lower cost.

Comparative study on corrosion behaviors of Mg-Al-Zn alloys

A comparative study on corrosion behaviors of various Mg-Al-Zn alloys(AZ21,AZ41,AZ61 and AZ91 series,cast under same cooling conditions and controlled alloying composition)was carried out.Scanning electron microscopy(SEM)and X-ray diffraction(XRD)were used for microstructural examinations.The corrosion behaviors were evaluated by immersion tests and potentiodynamic polarization measurements in 3.5%NaCl solution.The results showed that the influence of Al addition on corrosion resistance was more pronounced up to 4%(i.e.AZ41)above which its influence was at less extent.The deterioration of the corrosion resistance of the alloys,at higher Al contents,was attributed to the amount and morphology ofβ-Mg17Al12 intermetallics and the interruption of continuity of the oxide film on the surface of the alloys owing to coarsenedβintermetallics.

Microstructure and properties of Mg-Al binary alloys

The effects of different amounts of added Al, ranging from 1 % to 9 %, on the microstructure and properties of Mg-Al binary alloys were investigated. The results showed that when the amount of added Al is less than 5%, the grain size of the Mg-Al binary alloys decreases dramatically from 3 097 μm to 151 μm with increasing addition of Al. Further addition of Al up to 9% makes the grain size decrease slowly to 111 μm. The α-Mg dendrite arms are also refined. Increasing the amount of added Al decreases the hot cracking susceptibility of the Mg-Al binary alloys remarkably, and enhances the micro-hardness of the α-Mg matrix.

Nonisothermal dissolution kinetics on Mg17Al12 intermetallic in Mg-Al alloys

In this work,nonisothermal dissolution of intermetallic Mg_(17)Al_(12) in Mg-Al alloy has been firstly studied via Differential Scanning Calorimetry-DSC,X-Ray Diffraction-XRD and Scanning Electron Microscope-SEM as well as CALPHAD_based dissolution models and molecular dynamics simulation.The size and volume fraction of Mg_(17)Al_(12) phase could be predicted via the present kinetic dissolution model and agree well with experimental results.Also,the data-driven screening calculation shows that there is a range of temperature for significantly dissolving Mg_(17)Al_(12) phase,which could be increased with the increase of heating rate.The evolution of structural order for Mg_(17)Al_(12) phase has also been performed via molecular dynamics simulation with LAMMPS.The simulated results indicate that the structural order of Mg_(17)Al_(12) phase during heating is mainly affected by the Al-contained atomic pairs(Al-Al and Al-Mg),suggested that Mg atoms are thermodynamically and kinetically more active than Al atoms in Mg_(17)Al_(12) phase during heating,which has also been approved via the calculated atomic mobility of Mg and Al atoms in Mg_(17)Al_(12) phase in this work.Therefore,the atomic mobility of Mg atoms is mainly attributed to the interdiffusion coefficient of Mg_(17)Al_(12) phase which determines the dissolution of Mg_(17)Al_(12) phase during heating.The fundamental principle in this work could be used for other intermetallics and offers the greatly valuable information for optimizing the thermal processing in application of metal structural materials.

Mg-Al系阻燃镁合金的制备及性能研究

通过添加不同含量的Ca元素设计了一系列的梯度实验探求Mg-Al系合金中Ca元素的最佳含量。通过力学性能和阻燃性能的测试,发现随着Ca元素的添加,Mg-Al系合金的抗拉强度和规定非比例强度均有提升,但断后伸长率下降明显,添加了Ca元素的Mg-Al系合金比不添加Ca元素的Mg-Al系合金具有更好的阻燃性能。添加Ca和Y元素的Mg-Al系合金在1050℃火焰枪测试中表现出优异的阻燃性能,且抗拉强度和规定非比例强度均得到显著提升。

First principles investigation of binary intermetallics in Mg-Al-Ca-Sn alloy:Stability,electronic structures,elastic properties and thermodynamic properties

The structural stability, electronic structures, elastic properties and thermodynamic properties of the main binary phases Mg_（17）Al_（12）, Al_2Ca, Mg_2 Sn and Mg_2 Ca in Mg-Al-Ca-Sn alloy were determined from the first-principles calculation. The calculated lattice parameters are in good agreement with the experimental and literature values. The calculated heats of formation and cohesive energies show that Al_2Ca has the strongest alloying ability and structural stability. The densities of states（DOS）, Mulliken electron occupation number, metallicity and charge density difference of these compounds are given. The elastic constants of Mg_（17）Al_（12）, Al_2Ca, Mg_2 Sn and Mg_2 Ca phases are calculated, and the bulk moduli, shear moduli, elastic moduli and Poisson ratio are derived. The calculations of thermodynamic properties show that the Gibbs free energies of Al_2Ca and Mg_2 Sn are lower than that of Mg_（17）Al_（12）, which indicates that Al_2Ca and Mg_2 Sn are more stable than Mg_（17）Al_（12） phase. Hence, the heat resistance of Mg-Al-based alloys can be improved by adding Ca and Sn additions.

Mg-Al系耐热镁合金的研究进展

综述了不同合金元素强化Mg-Al系镁合金的最新研究进展,着重介绍了RE、Ca、Si和Sr等合金元素对Mg-Al系镁合金机械性能的影响,分析了Mg-Al系镁合金耐热性能的强化机理,并指出了Mg-Al系镁合金的发展方向。

Mg-Al系镁合金半固态坯料制备及触变挤压研究

采用拉伸试验机、金相显微镜和等径道角挤压等试验方法对Mg-Al系镁合金半固态坯料制备及触变挤压过程进行了研究。结果表明,等径道角挤压工艺对Mg-Al系镁合金有很好的应变诱导效果。经过等径道角挤压的Mg-Al系镁合金力学性能高,晶粒细小。等径道角挤压+等温处理方法制备的Mg-Al系镁合金半固态坯的微观组织晶粒细小,球化程度高,微观组织非常均匀。生产的AZ61、AZ80、AZ91D和AM60镁合金角框零件的微观组织细小,抗拉强度分别达到306.8、308.3、299.8、321.6MPa。伸长率分别达到21.6%、28.4%、14.6%和29.6%。

Mg-Al-Zn系镁合金挤压变形工艺研究

Mg-Al-Zn系镁合金性能的不足严重影响了其在航空航天等工业领域的应用,因此,对其进行组织及性能改进研究具有重要意义。本文阐述了Mg-Al-Zn合金挤压变形的主要方法,包括等通道角挤压、变通道角挤压、往复挤压、累积叠轧焊、等径角轧制、异步轧制、交叉轧制以及高压扭转技术等,分析了各种处理工艺对镁合金组织结构及其物理化学性能的影响。

MICROSTRUCTURE OF BINARY Mg-Al EUTECTIC ALLOY WIRES PRODUCED BY THE OHNO CONTINUOUS CASTING PROCESS

Directionally solidified binary Mg-Al eutectic alloy wires of approximately 5 mm in diameter were produced by the Ohno continuous casting （OCC） process and the microstructure was examined. It was found that the wires possess obvious unidirectional growth characteristic along its axial direction. The microstructure consists of parallel columnar grains that resulted from the competitive growth of equiaxed grains solidified on the head of dummy bar. Each columnar grain comprises regular eutectic a-Mg and β-Mg17 Al12 phases, which grew along the axial direction of the wires. The morphology of the eutectic is mainly lamellar, meanwhile rod eutectic exists. The formation of rod eutectic was attributed to the ＂bridging effect＂ caused by incidental elements in the alloy.

Revealing the nucleation event of Mg-Al alloy induced by Fe impurity

This study revealed the nucleation event and grain refinement mechanism of Mg-Al alloy induced by Fe impurity.The following orientation relationship was observed between Al-Fe particle andα-Mg matrix in the Mg-3Al alloy containing Fe impurity using a focused ion beam aided transmission electron microscope technique:(1^(-)011)[011^(-)1]_(Mg)//(011^(-))[011]_(Al_(2)Fe).Mg-3Al alloy was inoculated by adding 0.02wt%Fe to verify the nucleating potency of the Al_(2)Fe phase forα-Mg grain.The results indicated that Mg-3Al alloy was effectively refined with an average grain size declining from 1135 to 540μm.Among the potential Al-Fe phases of Mg-3Al-0.02Fe alloy,only the precipitation of the Al_(2)Fe phase occurs earlier than that ofα-Mg grain,and the Al_(2)Fe phase is stable in the nucleation stage ofα-Mg grain.Therefore,the Al_(2)Fe particle is the only available nucleating site for Mg-Al alloy with Fe impurity.The heterogeneous nucleation event ofα-Mg grain on the Al_(2)Fe particle is responsible for the grain refinement of Mg-3Al alloy inoculated by Fe.