Effect of melt-to-solid volume ratio and preheating temperature on Mg/Al bimetals interface by centrifugal casting

Compound casting is an efficient method for bonding dissimilar metals,in which a dramatic reaction can occur between the melt and solid.The centrifugal casting process,a type of compound casting,was applied to cast Al/Mg dissimilar bimetals.Magnesium melt was poured at 700 °C,with melt-to-solid volume ratios(Vm/Vs) of 1.5 and 3,into a preheated hollow aluminum cylinder.The preheating temperatures of the solid part were 320,400,and 450 °C,and the constant rotational speed was 1,600 rpm.The cast parts were kept inside the casting machine until reaching the cooling temperature of 150 °C.The result showed that an increase in preheating temperature from 320 to 450 °C led to an enhanced reaction layer thickness.In addition,an increase in the Vm/Vs from 1.5 to 3 resulted in raising the interface thickness from 1.2 to 1.8 mm.Moreover,the interface was not continuously formed when a Vm/Vs of 3 was selected.In this case,the force of contraction overcame the resultant acting force on the interface.An interface formed at the volume ratio of 1.5 was examined using scanning electron microscopy(SEM) equipped with energy-dispersive X-ray spectroscopy(EDS),and the results demonstrated the formation of Al_(3)Mg_(2),Al_(12)Mg_(17) and(δ+Al_(12)Mg_(17)) eutectic structures in the interface.

Segregation of Si and Mg at Fe(110)/Al(110) Interface

The interface structure and electronic properties of Fe(110)/Al(110) are investigated by the first-principles plane-wave pseudopotential method. The interface segregation position of Si and Mg is determined, and the effect of Mg and Si on the interface binding of Fe(110)/Al(110) is analyzed by combining the work of separation and charge density. The results show that the Fe(110)/Al(110) interface energy of FeHollow coordination is smaller and the interface structure is more stable. The Fe(110)/Al(110) interface separation surface in the form of Fe-Hollow coordination appears at the sub interface layer on the side of Al(110)near the interface. The interface structure of Mg and Si segregation is similar to that of undoped alloy elements.The calculations also suggest that Mg and Si segregate on the Al(110) side of the interface and occupy the Al lattice on the Al(110) side. The segregation of Mg and Si elements will reduce the interface binding, primarily because the Fe-Si bond and Fe-Mg bond are weaker than Fe-Al bond.

不同形貌Al-Fe金属的块体压制成形模拟研究

文章以含40%Al的Al-Fe复合金属为研究对象,对颗粒状和屑状40Al-Fe复合金属分别进行压制预变形,并对屑状40Al-Fe复合金属预制坯进行了二次热压缩变形,重点研究压制预变形及二次热压缩对Al-Fe复合金属成形性和界面影响。结果表明:压力为16 MPa时,颗粒状40Al-Fe复合金属预制坯(密度为4.54 g/cm^(3))成形性良好且形成致密界面;压力为16 MPa时,屑状40Al-Fe复合金属预制坯(密度为3.50 g/cm3)可以成形但界面存在孔洞,Al屑主要为“片层状”“狗牙状”“圆圈状”“波浪状”,其经二次热压缩变形,“圆圈状”Al屑连成一个整体,“狗牙状”与“波浪状”Al屑均演变为“片层状”,而Fe屑仍为“片层状”“块状”,未发生明显变形。变形温度300℃、变形速率0.5 s^(-1)、变形程度0.1是目前生产工艺最佳参数,此时屑状40Al-Fe复合金属成形性最佳且界面结合良好(密度为4.66 g/cm^(3))。

Preparation, interfacial regulation and strengthening of Mg/Al bimetal fabricated by compound casting: A review

Mg/Al bimetal combines the advantages of both aluminum and magnesium and has broad application prospects in automotive, aerospace,weapons, digital products and so on. The compound casting has the characteristics of low cost, easy to achieve metallurgical combination and suitable for the preparation of complex bimetallic parts. However, bimetallic joint strength is low due to differences of physical properties between Al and Mg, oxide film on metallic surface and interfacial Al-Mg IMCs, which is closely related to the interfacial microstructure and properties. Therefore, how to control the interface of the bimetal to achieve performance enhancement is the focus and difficulty in this field. At present, there are mainly the following strengthening methods. First, the “zincate galvanizing” and “electrolytic polishing+anodic oxidation” technology were exert on the surface of Al alloy to remove and break the oxide film, which improved the wettability between Al and Mg. Second, the undesirable Al-Mg IMCs were reduce or elimination by adding the interlayers(Zn, Ni and Ni-Cu). Thirdly, the evolution process of interfacial microstructure was changed and fine strengthening phases were formed by adding Si element to Al alloy or rare earth element to Mg alloy. Fourthly, mechanical vibration and ultrasonic vibration were applied in the process of the filling and solidification to refine and homogenize the interfacial structure. Finally, some other methods, including secondary rolling, thermal modification, heat treatment and constructing exterior 3D morphology, also can be used to regulate the interfacial microstructure and compositions. The above strengthening methods can be used alone or in combination to achieve bimetallic strengthening. Finally, the future development direction of the Mg/Al bimetal is prospected, which provides some new ideas for the development and application of the Mg/Al bimetal.

Improvement of the matrix and the interface quality of a Cu/Al composite by the MARB process

The matrix accumulative roll bonding technology （MARB） can improve the matrix performance of metal composite and strengthen the bonding quality of the interface./n this research, for the fwst time, the technology of MARB was proposed. A sound Cu/AI bonding composite was obtained using the MARB process and the bonding characteristic of the interface was studied using scanning electricity microscope （SEM） and energy-dispersive spectroscopy （EDS）. The result indicated that accumulation cycles and diffusion annealing temperature were the most important factors for fabricating a Cu/AI composite material. The substrate aluminum was strengthened by MARB, and a high quality Cu/AI composite with sound interface was obtained as well.

Effect of bonding interface on delamination behavior of drawn Cu/Al bar clad material

Cu/Al bar clad material was fabricated by a drawing process and a subsequent heat treatment.During these processes,intermetallic compounds have been formed at the interface of Cu/Al and have affected its bonding property.Microstructures of Cu/Al interfaces were observed by OM,SEM and EDX Analyser in order to investigate the bonding properties of the material.According to the microstructure a series of diffusion layers were observed at the interface and the thicknesses of diffusion layers have increased with aging time as a result of the diffusion bonding.The interfaces were composed of 3-ply diffusion layers and their compositions were changed with aging time at 400 °C.These compositional compounds were revealed to be η2,(θ+η2),(α+θ) intermetallic phases.It is evident from V-notch impact tests that the growth of the brittle diffusion layers with the increasing aging time directly influenced delamination distance between the Cu sleeve and the Al core.It is suggested that the proper holding time at 400 °C for aging as post heat treatment of a drawn Cu/Al bar clad material would be within 1 h.

Study on Interface between Sub-micron Particles and Matrix in Al_2O_3p/Al Composites

The microstructural characteristic of 1070AI matrix composites reinforced by 0.15 祄 AI2O3 particles whose volume fraction was 40% was investigated by TEM and HREM. The results showed that the interface between the matrix and reinforcements was clean and bonded well, without any interfacial reaction products. There were some preferential crystallographic orientation relationships between Al matrix and AI2O3 particle because of the lattice imperfection on the surface of Al2O3 particles.

Analysis of diffusion bond interface of TiAl base alloy with Ti, TC4 alloy and 40Cr steel

TiAl is diffusion bonded with Ti, TC4 Alloy and 40Cr Steel by heating in vacuum, and analysis of interfaces shows stratified Ti 3Al forms in TiAl/Ti interface closest to TiAl base, and the α phase and the α+β phase arise closest to Ti base at lower temperature and higher temperature respectively; Structure of TiAl/TC4 interface is TiAl/γ+α 2/Ti 3Al/α-Ti/TC4 at lower temperature and TiAl/γ+β+α 2/TC4 at high temperature; in TiAl/40Cr steel interface, obvious decarbonised layer on steel side while TiC and reaction phase with Fe Al Ti system form on TiAl side.

RELATIONS BETWEEN INTERFACE OF CF/Al-4.5 Cu COMPOSITE AND SOLIDIFICATION PROCESSING

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XRD and TEM Analysis in the Interface of Diffusion Bonding for Fe_3Al/Q235 Dissimilar Materials

Phase structure characteristics near the interface of Fe3Al/Q235 diffusion bonding are investigated by means of X raydiffraction (XRD), transmission electronic microscope (TEM) and electron diffraction, etc. The test results indicatedthat obviously a diffusion transition zone forms near the interface of Fe3Al/Q235 under the condition of heatingtemperature 1050~1100℃, holding time 60 min and pressure 9.8 MPa, which indicated that the diffusion interfaceof Fe3Al/Q235 was combined well. The diffusion transition zone consisted of Fe3Al and a-Fe(Al) solid solution.Microhardness near the diffusion transition zone was HM 480~540. There was not brittle phase of high hardness inthe interface transition zone. This is favorable to enhance toughness of Fe3Al/Q235 diffusion joint.

Mobility of Various Intervariant Interfaces in 18R Martensite in a Cu-Zn-Al Alloy Part Ⅰ: In-situ Observations

The motion of intervariant intedeces under the action of applied stress in the internally faulted 18R martensite in a Cu-Zn-Al shape memory alloy has been studied. Transmission electron microscopy in situ observations show that the interfaces between 24 martensite variants have different reaction to applied stress. The A/C type and A/B type interfaces have good mobil-ity, the A/D type interface has bad mobiIity, and the different-group-intervariant interfaces are basically immobile.

超声施振方式对消失模铸造Al/Mg双金属复合材料界面组织和力学性能的影响

研究了连续超声振动和间歇超声振动两种施振方式对消失模铸造Al/Mg双金属材料界面组织和力学性能的影响。结果表明,未施加超声振动Al/Mg双金属界面由Al-Mg金属间化合物区和共晶组织区组成,两个区域边界存在一层氧化膜,阻碍了元素扩散,Mg_(2)Si相呈网状,团聚分布于金属间化合物区。两种超声施振方式均能通过超声空化效应和声流效应破碎和消除氧化膜,并使Mg_(2)Si相细化和分散于整个界面,部分共晶组织转变为金属间化合物,提高了界面组织和显微硬度分布均匀性。连续超声振动作用下Al/Mg双金属界面剪切强度达到53.9 MPa,相比未超声处理提升63.8%。间歇超声振动作用下,界面厚度较连续超声振动减小,然而局部区域存在孔洞缺陷和Mg_(2)Si相局部聚集,削弱了对界面的强化效果,但界面剪切强度仍达到49.5 MPa。

PREPARATION,PROPERTIES AND INTERFACE STRUCTURES OF Si_3N_(4w)/6061Al COMPOSITE

The Si_3N_4 whisker reinforced 6061Al composite with bending strength of 790 MPa was prepared by squeeze casting process.After heat-treatment under T6 regime i.e.530℃, 1 h solutioning and 160℃,24 h aging,an increment in strength and microhardness may be over 20% and 28% respectively,The microstructures of Si_3N_4 whisker and Si_3N_4/Al interface were observed by meas of HRTEM.The relation between interracial structure and composite properties was discussed.

Effect of Nb and alloying elements on interface reaction between high Nb-containing TiAl alloys and ZrO_2-based ceramic moulds

In the present study, Ti-45Al-(6, 7, 8)Nb(at%) and Ti-45Al-8Nb-0.5(Mn, Si, Y, B) alloys were prepared by arc melting and casting into Zr O2(Y2O3 stabilized) ceramic moulds to study the effect of alloying elements Nb and Mn, Si, Y, B on the interfacial reaction between casting Ti Al alloys and ceramic moulds by SEM, and the elements' distribution in the interface reaction layer by line scanning. The results showed that with an increase in Nb content, the interfacial reaction weakened and the thickness of the reaction layer decreased gradually. The interface reaction thickness of the alloys with Nb content of 6, 7, 8at% were 60, 34 and 26 μm, respectively. Clearly, the addition of 8at% Nb to Ti-45 Al is the best for the thickness of the reaction layer. The addition of Nb would form a Nb-rich film in the reaction layer, which could reduce the solubility of oxygen in the interface, and suppress further diffusion of oxygen to the matrix. If the same content of Mn, Si, Y, or B alloying elements were added respectively to Ti-45Al-8Nb, the thickness of the interface reaction layer from large to small was as follows: Mn>Si>Y>B. The interface reaction thickness increased after 0.5at% Mn added, had no obvious change after 0.5at% Si addition, and decreased after adding 0.5at% Y or B. The introduced elements, which formed a protective film or/and promoted the formation of a dense aluminum oxide layer, would be of benefit to the resistance of interfacial reaction.

Stress distribution at diffusion-bonded interface of Fe_3Al with Cr18-Ni8 steel

Fe3Al and Crl8-Ni8 steel were bonded in vacuum and an interface was formed between Fe3Al and Crl8-Ni8 steel. Stress distribution at the diffusion-bonded interface was researched by numerical simulation and finite element method （FEM）. The results indicated that the peak stress appeared at the interface near Cr18-Ni8 steel side. This is the key factor to induce crack at this position. With the enhancement of heating temperature, the peak stress at the bonded interface increases. When the temperature is 1 100 22, the peak stress is up to 65.9 MPa, which is bigger than that at 1 000 22 by 9. 4%. In addition, the peak stress becomes bigger with the increase of the thickness of base metal from 1 mm to 8 ram. While the thickness is more than 8 ram, the peak stress varies slightly with the change of the thickness.

Interface states in Al_2O_3/AlGaN/GaN metal-oxide-semiconductor structure by frequency dependent conductance technique

Frequency dependent conductance measurements are implemented to investigate the interface states in Al2O3/A1GaN/GaN metal-oxide-semiconductor （MOS） structures. Two types of device structures, namely, the recessed gate structure （RGS） and the normal gate structure （NGS）, are studied in the experiment. Interface trap parameters includ-ing trap density Dit, trap time constant ιit, and trap state energy ET in both devices have been determined. Furthermore, the obtained results demonstrate that the gate recess process can induce extra traps with shallower energy levels at the Al2O3/AlGaN interface due to the damage on the surface of the AlGaN barrier layer resulting from reactive ion etching （RIE）.

Deformation-induced α_2/γ Interfaces in a Hot-deformed Ti-45Al-10Nb Alloy

The structure change of α2/γ interface in a Ti-45Al-10Nb alloy induced by hot deformation was investigated by conventional and high-resolution transmission eIectron microscopy. Two types of hot deformation induced special α2/γ intedeces, coherent intedeces with high density of ledges and semi-coherent α2/γ intedeces were found to be due to the absorption of mobile dislocations into the α2/γ inteface. For the misoriented semi-coherent α2/γ interfaces, the densities of dislocation ledges increase with the misoriented angle between (111)γ and (0001)α2 planes, and 1/3[111] Frank partial dislocations were involved in the dislocation ledges. Formation mechanism of these deformation-induced α2/γ interfaces was discussed to be related to the role of α2/γ interface5 adjusting the deformation as a dislocation sink absorbing the slipping dislocations in the γ phase

Ohmic Contact at Al/TiO_2/n-Ge Interface with TiO_2 Deposited at Extremely Low Temperature

TiO2deposited at extremely low temperature of 120°C by atomic layer deposition is inserted between metal and n-Ge to relieve the Fermi level pinning. X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy indicate that the lower deposition temperature tends to effectively eliminate the formation of GeOxto reduce the tunneling resistance. Compared with TiO2deposited at higher temperature of 250°C,there are more oxygen vacancies in lower-temperature-deposited TiO2, which will dope TiO2contributing to the lower tunneling resistance. Al/TiO2/n-Ge metal-insulator-semiconductor diodes with 2 nm 120°C deposited TiO2achieves 2496 times of current density at-0.1 V compared with the device without the TiO2interface layer case, and is 8.85 times larger than that with 250°C deposited TiO2. Thus inserting extremely low temperature deposited TiO2to depin the Fermi level for n-Ge may be a better choice.

Research of Trap and Electron Density Distributions in the Interface of Polyimide/Al2O3 Nanocomposite Films Based on IDC and SAXS

The distributions of traps and electron density in the interfaces between polyimide （PI） matrix and Al2O3 nanoparticles are researched using the isothermal decay current and the small-angle x-ray scattering （SAXS） tests. According to the electron density distribution for quasi two-phase mixture doped by spherical nanoparticles, the electron densities in the interfaces of PI/Al2O3 nanocomposite films are evaluated. The trap level density and carrier mobility in the interface are studied. The experimental results show that the distribution and the change rate of the electron density in the three layers of interface are different, indicating different trap distributions in the interface layers. There is a maximum trap level density in the second layer, where the maximum trap level density for the nanocomposite film doped by 25 wt% is 1.054 × 10^22 eV·m^-3 at 1.324eV, resulting in the carrier mobility reducing. In addition, both the thickness and the electron density of the nanocomposite film interface increase with the addition of the doped Al2O3 contents. Through the study on the trap level distribution in the interface, it is possible to further analyze the insulation mechanism and to improve the performance of nano-dielectric materials.

Mobility of Various Intervariant Interfaces in 18R Martensitein a Cu-Zn-Al AlloyPart Ⅱ: Some Theoretical Considerations

Detailed crystallographic analysis has been undertaken on the various combinations Of 24 martensite variants in the 18R martensite of a Cu-Zn-Al shape memory alloy. Based upon the calculated crystallographic data, the interface energy of different twin interfaces was calculated using a lowangle-grain-interface model. For the variant/variant pairs in a self-accommodating group. the A/C type and A/B type interfaces have low interface energy, and A/D type interface is an intermediate one. In contrast, the intervariant interfaces that belong to different plate groups have high intrface energy. The calculated results are consiStent with the previous observations of the mobility of intervariant interfaces.