稀土钡镁硅铁合金物相和显微组织分析

在成分（ｗｔ％）为ＲＥ２．９１、Ｂａ３．８５、Ｍｇ９．７０：Ｃａ２．２、Ａｌ１．５，余量为Ｆｅ的范围内，运用Ｘ－射线衍射分析及电子探针分析手段对ＲＥＢａＭｇＳｉＦｅ合金的物相和显微组织进行了分析。发现了稀土和碱土金属之间在硅基中的互溶现象并对其进行了初步鉴别。     

Effect of Microalloying on Wettability, Oxidation and Solidification Morphology of Sn-9Zn Alloy

EutecticorcloseneareutecticSn Pballoysare extensivelyusedinelectronicinterconnectionand packagingbecauseoftheirlowmeltingtemperatures, excellentwettabilitytocoppersubstratesandlow cost.Existingproductionlinesaredesignedonbasis ofSn Pbsolders.Withtheaccele…     

A Comprehensive Study of Diffusion Bonding of Mg AZ31 to Al 5754, Al 6061 and Al 7039 Alloys

In the present study, microstructural and mechanical properties of diffusion bonding of AZ31–Mg with Al 5754, Al 6061, and Al 7039 alloys were compared under same conditions. The vacuum diffusion processes were performed at a temperature of 440 °C, the pressure of 29 MPa, and a vacuum of 1?×?10^?4 torr for 60 min. The microstructural characterizations were investigated using optical microscopy and scanning electron microscopy equipped with EDS analysis and linear scanner. The XRD analysis was performed to study phase figures near the interface zone. The results revealed the formation of brittle intermetallic compounds like Al₁₂Mg₁₇, Al₃Mg₂, and their other combinations at bonding interfaces of all samples. Additionally, the hardness of Al alloys seemed to play a key role in increasing diffusion rate of magnesium atoms toward the aluminum atoms, with Al 6061 alloy having the highest diffusion rate. It consequently led to an increase in diffusion rate and thus formation of a strong diffusion bonding between magnesium and aluminum alloys. The highest strength was about 42 MPa for the diffusion bonding between Mg AZ31 and Al 6061. Further investigations on surfaces indicated that the brittle phases especially Al₃Mg₂ caused brittle fracturing.     

喷射沉积Al-12Si-0.6Mg合金的微观组织与性能

共晶合金具有良好的激光焊接性能,为提高电子封装盖板用Al-12Si合金的强度并保持良好的热物理性能,采用喷射沉积与热压烧结技术制备Al-12Si合金,研究添加0.6% Mg对合金微观组织、力学性能和热物理性能的影响。结果表明,喷射沉积/热压烧结Al-12Si合金中Si相呈近球形颗粒,平均直径为（4.5±0.2）μm,均匀分布于Al基体中;添加Mg未对Si相尺寸和形貌产生显著影响,但是在Al基体中形成Mg₂Si相。相对于Al-12Si合金,Al-12Si-0.6Mg合金的热导率降幅仅为4.2%,但是抗拉强度从154.1 MPa提高到190.1 MPa,增幅达到23.4%,该强度改善主要归因于固溶强化和析出强化作用。      

新型Al-1Mg-0.8Si-xCu铝合金均匀化工艺研究

Al-1Mg-0.8Si-xCu铝合金是汽车轻量化首选材料之一。采用光学显微镜、DTA分析、X射线衍射等分析检测手段,研究了Al-1Mg-0.8Si-xCu这一新型铝合金的均匀化工艺。结果表明,Cu元素含量为0.5%的Al-1Mg-0.8Si-xCu合金理想均匀化工艺为450℃×4 h+550℃×12 h,该工艺适用于Cu元素含量不大于1.05%的合金。     

Microstructure and Properties of Mg-10%Al-(0～3%)Di Alloys

The effects of didymium(Nd:Pr=3:1)on the microstructure and mechanical properties of Mg-10%Al alloy were studied with the additions of 0～3%Di. The small block-like Al2(Nd,Pr) phase appears in 1%Di alloy, the block-like Al2(Nd,Pr) and needle-like Al11(Nd,Pr)3 phases appear synchronously in 2%Di and 3%Di alloys, while the network of (Mg17Al12) β phase is broken up. The tensile properties can be improved with the addition of didymium. When the addition of didymium in Mg-10%Al alloy reaches 2%, the alloy exhibits the best combination of strength and ductility, but the strength and ductility drop at the addition of 3%Di due to the obvious increase of the size and quantity of the needle-like Al11(Nd,Pr)3 phase.     

Effect of rare-earth element additions on high-temperature mechanical properties of AZ91 magnesium alloy

The present article focuses on the high-temperature mechanical properties of the magnesium alloy AZ91. The addition of rare-earth (RE) elements up to 2 wt pct improves both yield and tensile strengths at 140 °C by replacing the Mg₁₇Al₁₂ phase with RE-containing intermetallic compounds. This intermetallic phase is thermally and metallurgically stable and is expected to boost the grain-boundary strengthening. It also increases the resistance of grain boundaries to flow at high temperatures. Further increases of RE additions reduce strength and ductility due to growth of the Al₁₁RE₃ brittle phase, which has sharp edges. Still, at a 3 wt pct RE addition, the strength of the alloy at high temperatures is more than that of AZ91.     

Wear-Resistance Performance of ZA-27 Alloys Reinforced by Rare Earth Compounds

In order to further improve wear-resistanceof the ZA-27 alloy and widen its applieationfields, St phase is added in the alloy[' '21. ButSt phase seriously cuts apart the alloy matrix.It not only decreases high toughness of the alloy, but also is harmful to its wear-resistance.On the basis of the researches in foregoing periodical on Zn-based alloy reinforced by Stphase and the inLfluence of RE on the high temperature mechanical properties of the ZA-27 alloy["'j, this paper deals with the e…     

Effect of Compositional Variation on the Microstructural Evolution and the Castability of Al–Mg–Si Ternary Alloys

This study examined the microstructural evolution and castability of Al–Mg–Si ternary alloys with varying Si contents. Al–6Mg–xSi alloys (where x = 0, 1, 3, 5, and 7; all compositions in mass pct) were examined, with Al–6 mass pct Mg as a base alloy. The results showed that in the ternary alloys with Si ≤ 3 pct, the solidification process ended with the formation of eutectic α-Al–Mg₂Si phases generated by a univariant reaction. However, in the case of ternary alloys with Si > 3 pct, solidification was completed with the formation of α-Al–Mg₂Si–Si ternary eutectic phases generated by a three-phase invariant reaction. In addition to the eutectic Mg₂Si phases, the primary Mg₂Si phases formed in each of the ternary alloys, and the size of both sets of phases increased with increasing Si content. The two-phase eutectic α-Al–Mg₂Si nucleated from the primary Mg₂Si phases. The inoculated Al–6Mg–1Si alloy had the smallest grain size. Moreover, the grain-refining efficacy of the Al–5Ti–B master alloy in the ternary alloys decreased with increasing Si content in the alloys. Despite the poisoning effect of Si on the potency of TiB₂ compounds in the inoculated Al–6Mg–1Si alloy, the grain size of the alloy was slightly smaller than that of the Al–6Mg binary alloy. This resulted from the increasing growth restriction factor (induced by Si addition) of the Al–6Mg–1Si alloy. In terms of the castability, the examined alloys showed different levels of susceptibility to hot tearing. Among the alloys, the ternary Al–6Mg–5Si alloy exhibited the highest susceptibility to hot tearing, whereas the Al–6Mg–7Si exhibited the lowest. The severity of hot tearing initiated by the unraveling of the bifilm was determined by the freezing range, grain size, and the amount of eutectic phases at the end of the solidification process.

     

Effect of Rare Earth on Microstructure of Vacuum Melting Ni-Based Self-Fluxing Alloy Coatings

The Ni-based self-fluxing alloy coating containing RE was acquired by the technique of vacuum melting on the hypoeutectoid steel (Fe-0.45% C) matrix. By X-ray diffraction, SEM and EDX, the microstructure and phase structure of section of coating and the microstructure near the interface between coating and matrix were investigated, and the effect of RE on microstructure of coating was also discussed. The results show that the microstructure of the NiCrBSi alloy coating is composed of Ni-based solid solution and a lot of massive, globular and needle secondary phases CrB, Ni3B, Cr7C3, Cr23C6 among the solid solution. The metallurgical binding between steel matrix and coating is realized. RE makes needle phase of alloy coating vanish. New phases of NiB and Cr6.5Ni2.5Si are precipitated from alloy coating, and secondary phases of alloy coating are sphericized. Consequently, RE also hinders the diffusion of Ni, Cr and Si atoms from coating to matrix and Fe atoms from matrix to coating, holds back the dilution of Fe for NiCrBSi alloy coating, and assures the chemical composition of the alloy coating.     

激光熔覆IMC涂层的热疲劳性能

研究了激光熔覆和Ｎｉ－Ａｌ合金涂层及（Ｎｉ－Ａｌ）＋ＷＣ复合涂层的热疲劳性能。结果表明，涂层疲劳损伤形式为沿晶应力（氧化）腐蚀。腐蚀产物为Ａｌ２Ｏ３。每次热循环后，熔覆层中的最终残余应力是残余热应力和相变应力共同作用的结果。由于复合涂层中的残余应力为压应力，而合金涂层中的残余应力为拉应力，因此前热疲劳性能优于后者。     

Effect of Ca and Rare Earth Additions on the Texture,Microhardness, Microstructure and Structural Properties of As-Cast Mg–4Al–2Sn Alloys

In this work, alloys with nominal composition of Mg–4Al–2Sn–xRE–yCa (where RE = rare earth, x = 0, 1, 3 and y = 0, 1) have been prepared using tilt casting method. Prepared as-cast samples have been investigated by X-ray diffractometry, optical microscopy and scanning electron microscopy techniques as well as hardness measurement. The texture, microstructure and structural parameters of samples were also refined from X-ray diffraction patterns utilizing the Rietveld method and generalized spherical-harmonic model. It was found that with addition of rare earth and calcium elements, intermetallic phases of γ-Mg₁₇Al₁₂ and β-Mg₂Al₃ disappeared in cast alloys while small amount of Al₁₁RE₃ and CaMgSn intermetallics phases are formed. The texture factor of α-Mg as a main phase of samples was decreased with addition of rare earth up to 1 % and increased with more addition of rare earth elements. According to the results, with addition of rare earth elements, texture of Mg phase changes from 〈112〉 direction to 〈100〉 and 〈002〉 directions while Ca addition causes the texture in 〈002〉 direction. The microhardness of Mg–4Al–2Sn alloy was enhanced with addition of rare earth and calcium elements which is in agreement with the expected trend based on computed phase fraction of the samples. Addition of 1 wt% of calcium causes a dramatic change in the morphology and chemical composition of intermetallic phases, from acicular shape with composition of Al₁₁RE₃ into fine feather of CaMgSn intermetallic phase which accumulated in cluster morphologies in interdendritic regions.     

Three-Ply Al/Mg/Al Clad Sheets Fabricated by Twin-Roll Casting and Post-treatments (Homogenization,Warm Rolling,and Annealing)

When thin Al alloy sheets are clad on to twin-roll-cast Mg alloy melt, inherent drawbacks of Mg alloys such as poor formability, corrosion resistance, and surface quality can be effectively complemented. In this study, three-ply Al/Mg/Al clad sheets were fabricated by twin-roll casting and post-treatments. Brittle interfacial layers composed of γ (Mg₁₇Al₁₂) and β (Mg₂Al₃) phases were inevitably formed, but their proper thickening during the post-treatments led to improvement of interfacial bonding and resultant tensile properties. In particular, warm rolling was an effective way to modify interfacial microstructures and tensile properties by minimizing deformation inhomogeneity and stress concentration.     

Wear-Resistance Performance of ZA-27 Alloys Reinforced by Rare Earth Compounds

The morphology of ZA-27 alloy reinforced by RE compounds and its wear-resistance were studied. It is found that some nodular second phases appear due to the addition of Si and RE, which can disperse in grain boundaries or between dendrite crystals so that the alloy has been refined. Energy spectrum analysis of scanning electron microscope shows that the second phases are complex compounds containing RE, Al, Zn and Si. The micro-hardness test indicates that micro-hardness values of the compounds are higher than those of the matrix. The wear-resistance of ZA-27 alloy reinforced by RE compounds is 4 times as high as that of ZA-27 alloy and also higher than that of ZA-27 alloy containing Si phase. The impact toughness of the alloy containing RE and Si is higher than that of the alloy containing Si.     

Effect of Mg on Solidification Microstructures of Homogenous and Functionally Graded A390 Aluminum Alloys

Hypereutectic Al?CSi alloys are used in components that require high resistance wear and corrosion, good mechanical properties, low thermal expansion and less density. The size and morphology of hard primary silicon particles present in Al?CSi alloys greatly influences the mechanical properties. Addition of Mg leads to formation of intermetallic Mg₂Si phases, which contributes towards the properties of high silicon alloy as well as alters the nature and quantity of primary silicon formed. The high silicon alloy subjected to centrifugal casting leads to the formation of functionally gradient material, which provides variation in spatial and continuous distribution of primary phases in a definite direction exhibiting selective properties and functions within a component. The present study is to evaluate the effect of Mg on solidification microstructures of homogenous and functionally graded A390 aluminium alloys. The addition of Mg from 3 to 5?% in A390 alloy using Al?C20Mg master alloy has shown a transformation from primary silicon rich matrix to Mg₂Si rich matrix. Centrifugal casting shows the gradient distribution of primary silicon and Mg₂Si phases towards the inner periphery of the casting.     

Influence of Strontium Addition on Microstructure and Mechanical Properties of an Al–10Si–5Cu Alloy

The microstructure and mechanical properties of Al–10Si–5Cu cast alloys with micro-addition of alloying elements (V, Cr and Ni) were studied before and after strontium addition. Samples were examined using the X-Ray diffraction, the optical microscope, the scanning electron microscope and the energy dispersive spectrometer. The results indicated that the α-Al matrix, eutectic Si phase and Al₂Cu phase were the main constituent phases of Al–10Si–5Cu alloys before or after strontium addition. Strontium addition affected the refining of the α-Al grains and transforming the configuration of interdendritic phases. The un-modified alloy showed a brittle nature because of existing brittle and aggregated AlSiMnFe phases. Contributing to the alteration of microstructure in strontium modified alloy, the strength and elongation of the alloy were improved. In addition, the fracture mechanism and crack propagation process were investigated in both the alloys.     

Elastic Properties,Thermal Expansion Coefficients,and Electronic Structures of Mg and Mg-Based Alloys

Ab-initio density functional theory (DFT) calculations were performed to study alloying effects on hcp Mg. The alloy solid solution strengthening represented by bond strength enhancement in alloys, elastic properties, thermal expansion coefficients, and electronic structures of Mg-based alloys was investigated. Results show that alloying additions with sp-metal Al and rare earth (RE) Y are capable of increasing the bond strength, with the addition of Y achieving a better effect. The bond strength enhancement due to an RE Y addition is associated with a hybridization between the d-orbital of Y and the p-orbital of the Mg atoms near the Fermi energy, and this was consistent with the electron localized function (ELF) evaluations showing that more localized and stronger covalent bonds are formed between Y and Mg atoms. It is also found that alloying additions of Al, Zn, and Y are not capable of increasing elastic coefficients and moduli, indicating that bond strength enhancement could play a major role in alloy solid solution strengthening in Mg-based alloys. Possible reasons for the elastic properties accompanying the alloying addition are given from the electronic point of view. Furthermore, from the calculated negative Cauchy pressure (C ₁₃ – C ₄₄ < 0), it is concluded that the chemical bonds between Y and Mg atoms show angular characteristics.     

Effect of Rare Earth on Microstructure of γ-TiAl Intermetallics

The rare earth (RE) elements (Ce, La) were added to binary Ti-47% Al alloys (atomic fraction) by Induction Skull Melting. The element Ce of 1.0 atomic percent was added individually, and La of 0.2 atomic percent was added individually. This article studied the influences of rare earth metal (Ce, La) on microstructure of as-cast TiA1 based alloy by XRD, SEM, EMPA and TEM measurement methodology. The results show that most of rare earth-rich phases (AlCe, Al-La) are uniformly distributed in grain boundary in the shape of discontinuous network, and some particles of rare earthrich phases within the grains are mainly ellipsoids. In addition, rare earth element can obviously refine the grain size and the lamellar thickness of as-cast TiAl based alloy samples. The grain size of Ti-47Al-1.0Ce-0.2La alloy reaches about 30～80μm, and the lameUar thickness of its γ phase and α2 phase are less than 200 and 20nm, respectively.     

Mechanism of Effects of Rare Earths on Microstructure and Properties at Elevated Temperatures of AZ91 Magnesium Alloy

By using real-space recursion method,the energetics of the undoped and Al and/or RE atoms doped 7（1450）〈0001〉 symmetric tilt grain boundaries（GBs）in AZ91 alloys were investigated.Similar calculations were performed on undoped and doped bulk α Mg for comparison.The results showed that Al atoms segregated at GBs in AZ91 alloys.When RE atoms were added,they also segregated at GBs,and their segregation is stronger than Al atoms＇.Therefore,RE atoms retard the segregation of Al atoms.Calculations of interaction energy indicated that Al atoms repelled each other,and could form ordered phase with host Mg atoms.On the contrary to the case of Al,RE atoms attracted each other,they could not form ordered phase with Mg,but could form clusters.Between RE and Al,there existed attractive interaction,and this attractive interaction was the origin of Al11RE3 precipitation.Precipitation of Al11RE3 particles with high melting point and high thermal stability along GB improves high temperature properties of AZ91 alloys.     

Development of an Aluminized Multi‐Phase Steel with Dual Phase Properties for High Temperature Corrosion Resistance Applications

A high strength, high Mn, Cr‐Mo containing multi‐phase steel grade was aluminized with a 90 wt% Al – 10 wt% Si alloy coating, using a laboratory hot‐dip simulator. The adhesion of the coating to the steel strip was evaluated and the microstructure of the as deposited material was assessed. The coated sheet steel was tested at high temperatures by monitoring the weight gain of the samples and their mechanical properties as a function of time. It was found that the thermal properties of the aluminized sheet were excellent. The analysis of the coating/substrate interface revealed the dissolution of brittle intermetallic phases, explaining the excellent high temperature resistance performance of the Al‐Si coating up to temperatures as high as 900°C. In addition, the use of a continuous annealing cycle common in current aluminizing lines, resulted in a dual phase microstructure.