Relationship between elements migration ofα-AlFeMnSi phase and micro-galvanic corrosion sensitivity of Al-Zn-Mg alloy

First principles calculations and scanning Kelvin probe force microscopy(SKPFM)were used to investigate the effect of elements migration ofα-AlFeMnSi phase on micro-galvanic corrosion behavior of Al-Zn-Mg alloy.The simulation results showed that the average work function difference between theα-AlFeMnSi phase and Al matrix decreased from 0.232 to 0.065 eV due to the synchronous migration of elements Fe-Mn-Si.Specifically,as the elements Fe-Si migration during the extrusion process,the average Volta potential difference detected by SKPFM between theα-AlFeMnSi phase and Al matrix dropped down to 432.383 mV from 648.370 mV.Thus,the elements migration reduced the micro-galvanic corrosion sensitivity of Al-Zn-Mg alloy.To reach the calculated low micro-galvanic tendency betweenα-AlFeMnSi phase and Al matrix,the diffusion of Mn should be promoted during extruding process.

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.

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.

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.

铸轧Al-Zn-Mg-Cu-Sc-Zr合金短流程制备及组织性能研究

通过Sc元素微合金化和电磁场获得了无中心偏析、带状晶间偏析细小和组织均匀分布的铸轧Al-Zn-Mg-Cu-Sc-Zr(以下称“7xxx系”)铝合金板材,并设计了适用于铸轧组织特征的新型短流程轧制-热处理工艺路线(以下简称“短流程工艺路线”)。短流程工艺路线在轧制破碎粗大结晶相和缩小元素扩散距离的作用下,结晶相显著细化,并在中间短时均匀化和固溶处理过程中快速溶解。与传统工艺路线下的T6态样品相比,尽管短流程工艺路线省略了长时间均匀化工艺,但其结晶相溶解更加充分,残余结晶相和晶粒组织显著细化。在传统工艺路线下,C-T6板材的屈服强度、抗拉强度和延伸率分别为568 MPa、618 MPa和8.7%。在短流程工艺路线下,S-T6样品依然保持了良好的力学性能,相应性能分别为551 MPa、605 MPa和10.4%。

Experiments and modeling of double-peak precipitation hardening and strengthening mechanisms in Al-Zn-Mg alloy

The aim of the present work is to develop a model for simulating double-peak precipitation hardening kinetics in Al-Zn-Mg alloy with the simultaneous formation of different types of precipitates at elevated temperatures based on the modified Langer-Schwartz approach. The double aging peaks are present in the long time age-hardening curves of Al-Zn-Mg alloys. The physically-based model, while taking explicitly into account nucleation, growth, coarsening of the new phase precipitations and two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing）, was used for the analysis of precipitates evolution and precipitation hardening during aging of Al-Zn-Mg alloy. Model predictions were compared with the measurements of Al-Zn-Mg alloy. The systematic and quantitative results show that the predicted hardness profiles of double peaks via adding a shape dependent parameter in the growth equation for growth and coarsening generally agree well with the measured ones. Two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing） were considered operating simultaneously in view of the particle size-distribution. The transition from shearing to bypassing strengthening mechanism was found to occur at rather early stage of the particle growth. The bypassing was found to be the prevailing strengthening mechanism in the investigated alloys.

Effect of flame rectification on corrosion property of Al-Zn-Mg alloy

The corrosion resistance of Al？Zn？Mg alloy subjected to different times in flame rectification was investigated based on the exfoliation corrosion test. The results indicate that the flame rectification deteriorates the exfoliation corrosion resistance of Al？Zn？Mg alloy. The corrosion resistance of Al-Zn-Mg alloy is ranked in the following order： base metal〉two times〉three times〉one time of flame rectification. The exfoliation corrosion behavior was discussed based on the transformation of precipitates at grain boundaries and matrix. With increasing the number of times in flame rectification, the precipitate-free zones disappeared and the precipitates experienced dissolution and re-precipitation. The sample was seriously corroded after one time of flame rectification, because the precipitates at grain boundaries are more continuous than those in other samples.

Determination of kinetic parameters from calorimetric study of solid state reactions in 7150 Al-Zn-Mg alloy

Differential scanning calorimetric （DSC） study was carried out at different heating rates to examine the solid state reactions in a 7150 A1-Zn-Mg alloy in water-quenched （WQ） state, naturally and artificially aged tempers. The exothermic and endothermic peaks of the thermograms indicating the solid state reaction sequence were identified. The shift of peak temperatures to higher temperatures with increasing heating rates suggests that the solid state reactions are thermally activated and kinetically controlled. The artificial aging behaviour of the alloy was assessed by measuring the variations of hardness with aging time. The fraction of transformation （Y）, the rate of transformation （dY/dt）, the transformation functionflY）, and the kinetic parameters such as activation energy （Q） and frequency factor （k0） of all the solid state reactions in the alloy were determined by analyzing the DSC data, i.e. heat flow involved with the corresponding DSC peaks. It was found that the kinetic parameters of the solid state reactions are in good agreement with the published data.

Microstructure and impact mechanical properties of multi-layer and multi-pass TIG welded joints of Al-Zn-Mg alloy plates

The microstructure and mechanical properties of multi-layer multi-pass TIG welded joints of Al-Zn-Mg alloy plates were studied.The phase constituent and microstructure of different regions of the welded joints were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),transmission electron microscopy(TEM)and energy disperse spectrum(EDS),while the mechanical properties were evaluated according to the impact test.A dispersively distributed spherical and needle-likeη(MgZn2)phase was obtained in the welding seam.The phase composition of the heat-affected zone(HAZ)wasα(Al)+η(MgZn2)+Al6Mn,and there were a large number of dispersively precipitated nanoscale particles.The welded joint zone had the highest impact toughness as compared with the other parts of the joint.The MgZn2 phase in the weld zone contributed to the improved toughness of the joint.Al2 MgCu phase in HAZ was proven to act as a crack source during fracture.

Ageing Effect on Hardness and Microstructure of Al-Zn-Mg Alloys

Experimental results of the investigation on the hardness of two Al-Zn-Mg alloys [Al-10.0 Zn-4.0 Mg and Al-8.5 Zn-3.0 Mg (wt pct)] aged in the temperature range 60～310℃ for different intervals of time from 1/4 h to 168 h are presented. Both the alloys were found to show identical behaviour of hardness with ageing time. Alloy with higher Zn and Mg content had higher hardness than the alloy with lower solute content. There were three ranges of temperature in which different types of precipitates formed and affected the hardness. Some of the grain boundaries were found to migrate and precipitate free zone has been observed.

Solidification path calculations of Al-Zn-Mg alloys in Al-rich corner

The solidification paths of Al-Zn-Mg alloys in the Al-rich corner were investigated. The thermodynamic data for the calculation are obtained by direct coupling with the CALPHAD software Thermo-Calc via its TQ6-interface and the COST2 database. The influences of the initial compositions and the extent of solid back diffusion on the solidification path were numerically investigated by sample calculation of the ternary Al-Zn-Mg alloys. The calculation results of solidification paths of the selected alloys: Al-Zn-3 Mg(in wt.%), Al-5 Zn-10 Mg, Al-2.5Zn-15Mg, Al-10Zn-20.5 Mg, Al-8Zn-25 Mg, were: L→(L+α-Al), L→(L+α-Al)→(L+α-Al+TAU), L→(L+α-Al)→(L+α-Al+Al Mg_β), L→(L+α-Al)→(L+α-Al+TAU)→(L+α-Al+TAU+Al Mg_β), L→(L+α-Al)→(L+α-Al+Al Mg_β)→(L+α-Al+TAU+Al Mg_β), respectively. The results show that the initial compositions and the extent of solid back diffusion have a great influence on solidification path, and the amounts of eutectic phase increase with the decrease of the solid back diffusion coefficient. The equilibrium solute partition coefficients for Zn and Mg in alloys are also calculated and their influence on micro-segregation in the primary solidification of Al-5Zn-10 Mg alloy is analyzed.

Fracture Toughness of Cast Al-Zn-Mg Alloys

Compact tension specimens of as-cast Al-3Zn-2Mg and Al-7Zn-2Mg (in wt pct) alloys were subjected to fracture toughness tests at room temperature according to specification5 laid down in ASTM E-399-81. It was found that increasing the Zn content, grain refinement and increasing the solidification rate lead to an increase in the fracture toughness of the material.

SUPERPLASTICITY OF Al-Zn-Mg-Zr-RE AND Al-Zn-Mg-Ti ALLOYS AND THEIR CAVITATION BEHAVIOUR DURING DEFORMATION

The superplasticity of the Al-Zn-Mg-Zr-RE(alloy A)and Al-Zn-Mg-Ti(alloy B),their change of volume fraction of metastable micro-cavities under various reduction of area and strain rates,as well as the growth of stable cavities in them have been studied by means of small angle X-ray scattering analyses and quantitative metalloraphy respectively.Experimen- tal results show that the volume fraction of metastable micro-cavities of the alloy A is more than that of the alloy B,but the growth rate of stable cavities in alloy A is less than that in al- loy B.Thus,it is believed that the superplasticity of alloy A is superior to that of alloy B.

高强韧Al-Zn-Mg-Cu铝合金在海洋工程装备中的应用展望

可热处理强化的高强韧Al-Zn-Mg-Cu系铝合金具有塑韧性好、密度小和力学性能好等优点,在海洋装备中具有广泛的应用前景。但铝合金在服役过程中仍然存在少许缺陷,如:海洋环境下的腐蚀问题,遭受风浪冲击的海洋结构物的焊缝强度问题等。以7075铝合金为研究对象,查阅了近五年海洋工程装备材料的相关研究,从表面处理、焊接技术、热处理工艺三方面介绍了高强度铝合金的研究应用现状,提出了海工装备用高强铝合金的研究方向。

7000系高强铝合金微观组织结构对应力腐蚀行为和机制影响的研究进展

7000系(Al-Zn-Mg-Cu)高强铝合金是铝合金中强度最高的系列之一,应力腐蚀开裂(SCC)是影响其服役安全稳定性的关键因素。综述了应力腐蚀开裂的阳极溶解机制和氢致开裂(HIC)机制,总结了7000系铝合金中的组织结构对合金SCC行为及机制的影响;从合金化学成分、热处理、预应变、表面处理等方面对SCC敏感性的影响出发,论述了不同组织结构对SCC行为的影响。提出了降低7000系高强铝合金SCC敏感性的重点研究方向:通过优化合金元素、使用新型的热处理工艺和表面处理技术等方法合理调控合金的微观组织结构,进而延长合金的使用寿命,使材料受到更好地保护。

CoCrMo和CoCrMoW合金的组织结构、力学性能及在小牛血清溶液中的腐蚀摩擦学性能研究

为了明确CoCrMo和CoCrMoW合金在小牛血清溶液中的腐蚀摩擦行为和耐腐蚀磨损机制,使用真空熔炼技术制备CoCrMo和CoCrMoW合金,采用SEM-EDS、TEM、XRD、压缩力学性能试验和腐蚀磨损试验研究2种合金的组织结构、力学和腐蚀摩擦学性能。结果表明:2种合金均由γ-Co和ε-Co组成,且微观组织以等轴晶为主。CoCrMo合金展现出优异的压缩力学性能,且其在小牛血清溶液中具有良好的耐腐蚀性,而CoCrMoW合金出现点蚀。2种合金在小牛血清溶液中具有较好的腐蚀摩擦学性能,其摩擦系数和磨损率分别为0.11~0.21和1.01×10^(-6)~2.46×10^(-6)mm^(3)/(N·m)。随着载荷和频率的增加,2种合金的摩擦系数降低,实时摩擦系数稳定性提高。在低载荷条件下,合金的耐腐蚀磨损性能随频率的增大而增强,其磨损机制以磨粒磨损为主;在高载荷条件下,合金的磨损率随频率的增加而增大,磨粒磨损和腐蚀磨损并存。总体而言,CoCrMo合金的耐腐蚀磨损性能优于CoCrMoW合金,这主要是因为CoCrMo合金具有较好的压缩力学性能和耐腐蚀性能。

敏化处理对AA5083铝合金的腐蚀和应力腐蚀开裂行为的影响

铝镁系合金被广泛用于船舶建造和海洋结构,但是在服役过程中会在晶界析出低腐蚀电位的富镁相,引起环境断裂问题。研究了175℃/100 h敏化处理对铝合金AA5083的Al-Mg相析出行为、晶间腐蚀、电化学行为和应力腐蚀开裂性能的影响,并采用慢应变速率拉伸试验研究敏化前后的应力腐蚀开裂敏感性。结果表明,原始态材料不发生晶间腐蚀和应力腐蚀开裂,而经过敏化处理后,100 nm厚的β'-Al_(3)Mg_(2)或β-Al_(3)Mg_(2)相在晶界析出,导致材料发生严重的晶间腐蚀、电化学腐蚀以及应力腐蚀开裂。铝合金的应力腐蚀开裂行为是在裂纹尖端析出相的阳极溶解以及溶液酸化引发氢脆的协同作用下发生的。

Characterization of dynamic microstructural evolution of AA7150 aluminum alloy at high strain rate during hot deformation

The AA7150 aluminum alloy was compressed to various strains at strain rate of 10 s（-1） and temperatures of 300 °C and 450 °C, respectively. Flow stress behavior, substructure evolution, morphology and spatial distribution of precipitates were studied based on differential scanning calorimetry analysis and transmission electron microscope observation. The results showed that dynamic flow softening occurs during hot deformation. The main softening mechanism could be concluded as dynamic recovery at 300 °C and continuous dynamic recrystallization at 450 °C. The clear heterogeneous spatial distributions of precipitates are found during deformation and enhanced with increased strain. Higher contents of Cu in T phases are found at 450 °C than at 300 °C, which present a transformation process from T phases to S phases as well. The associated evidence of dynamic precipitation on dislocations and particle-stimulated nucleation, as well as the detailed microstructural inherited relationship and morphological texture（particles preferred orientation） were characterized.