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.

Nucleation and growth mechanisms of γ〞 phase with single-unit-cell height in Mg-RE-Zn(Ag) series alloys: a first-principles study

The highly thermal stability precipitates strengthen creep resistance for alloys,which require precipitates to resist coarsen at elevated temperature.In the Mg-RE-Zn(Ag)series alloys,the key strengthening phase-γ"phase,remains its single-unit-cell height throughout aging process.The origin of such extremely thermal stability ofγ"phase is still unclear.By using the first-principles calculations,it is found that the formation ofγ"phase introduces compressive strain to its surroundingα-Mg lattice and simultaneously alter charge distribution ofα-Mg lattice near theα-Mg/γ"hetero-interface.These two variations overα-Mg lattice lead to lower vacancy formation energies and migration energy barriers for solute atoms near theα-Mg/γ"hetero-interface in comparison with that of bulk condition.Consequently,the variations facilitate rapid diffusion of solute atoms near theγ"phase and promote nucleation rate of otherγ"plates around it.On the basis of ledge-thickening model,the origin of nucleation/growth ofγ"phase with single-unit-cell height was explained.Thermodynamically and kinetically,the solute atoms are not apt to migrate into the nearest basal plane adjacent to theγ"phase.Moreover,the lower aging temperature(~200℃)and almost completely coherentα-Mg/γ"hetero-interface lead to the ledges are extremely hard to nucleate on the hetero-interface.Therefore,γ"plates maintain single-unit-cell height throughout aging process.

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.

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.

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.

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.

Changes of microstructure of different quench sensitivity 7,000 aluminum alloy after end quenching

The quench sensitivity and their influential factors of 7,021, 7,085, and 7,050 alloys were investigated by the end quenching test method and the measurement of electrical conductivity, hardness, and microstructure after aging. The results indicate that 7,050 alloy has the largest changes with hardness decreasing from HV 199 to HV 167,and electrical conductivity increases from 16.6 to18.2 MS m-1when the distance from quenched end increases from 2 to 100 mm. Alloys 7,085 and 7,021 have relatively smaller changes. According to the relationship between the hardness and electrical conductivity of a supersaturated solid solution, 7,050 alloy has higher quench sensitivity than 7,085 and 7,021 alloys. The microstructure of 7,050 alloy with higher major alloy element（Zn ？ Mg ？ Cu） addition and Cu element addition is mostly affected by the changes of distance from quenched end. In 7,050 alloy, the size of intragranular precipitates is from about 10-200 nm, and the（sub） grain boundary precipitates are about 20-300 nm. Alloy 7,085 with lower Cu content is moderately affected, while 7,021 is least affected. It is found that with the increase of distance from quenched end, quenched-induced precipitate preferentially nucleates and grows in the（sub） grain boundary and then on the pre-existing Al3 Zr particles.