The Effect of Alloying Elements on the Microstructure of Al-5Fe Alloys

The effects of adding Cr, Mn, and Zr on the microstructure of Al-5Fe alloys has been studied by metallographic analysis, scanning electron microscopy, x-ray diffraction analysis, and differential thermal analysis. It has been found that the effects of the different elements on the microstructure of ferro-aluminum intermetallics in Al-5Fe alloys are not alike. Addition of Cr in Al-5Fe alloys dissolves only into AlFe intermetallics, resulting in the morphology of the AlFe phases being changed with increasing Cr content. Cr is a favorable nucleating agent for encouraging metastable Al _x Fe (x = 4.6 to 5.0) phase formation. Adding Mn in Al-5Fe alloys may stabilize the metastable Al₆Fe phase, helping the primary phase field of Al₇Cr diminish or even disappear and forcing Cr to dissolve into AlFe phases. Adding Zr does not refine the primary AlFe intermetallics. Al₃Zr particles in Al-5Fe alloys will occupy the growing spaces of ferro-aluminum phases and indirectly hinder the growth of Fe-bearing phases.     

Effect of minor Sc and Zr addition on microstructures and mechanical properties of Al-Zn-Mg-Cu alloys

Three kinds of Al-Zn-Mg-Cu based alloys with 0.22%, 0.36%（Sc＋Zr） （mass fraction, %）, and without Sc, Zr addition were prepared by ingot metallurgy. By using optical microscopy, transmission electronic microscopy and scanning electron microscopy, the effects of microalloying elements of Sc, Zr on the microstructure of super-high-strength Al-Zn-Mg-Cu alloys related to mechanical properties were investigated. The tensile properties and microstructures of the studied alloys under different heat treatment conditions were studied. The addition of minor Sc, Zr results in the formation of Ala（Sc,Zr） particles. These particles are highly effective in refining the microstructures, retarding recrystallization, pinning dislocations and subboundaries. The strength of Al-Zn-Mg-Cu alloys was greatly improved by simultaneously adding minor Sc, Zr, meanwhile the ductility of the studied alloys remains at a higher level. The 0.36%（Sc＋Zr） alloys gain the optimal properties after 465 ℃/h solution and 120 ℃/24 h aging. The increment of strength is mainly due to strengthening of fine grain and substructure and precipitation ofAl3（Sc, Zr） particles.     

Effect of three-step homogenization on microstructure and properties of 7N01 aluminum alloys

The effect of different homogenization treatments on the microstructure and properties of the 7N01 aluminum alloy was investigated using hardness measurements, electrical conductivity measurements, tensile and slow strain rate tests, electron probe microanalysis, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results revealed that three-step homogenization improved the uniformity of Zr distribution by eliminating segregation of the main alloying elements. During the second homogenization step at 350 °C for 10 h, coarse and strip-like equilibrium η phases formed which assisted the nucleation of Al₃Zr dispersoids and reduced the width of the precipitate-free zone of A1₃Zr dispersoids. As a result, coarse recrystallization was greatly reduced after homogenization at 200 °C, 2 h + 350 °C, 10 h + 470 °C, 12 h, which contributed to improving the overall properties of the 7N01 aluminum alloys.     

Quasi-peritectic solidification reactions in 6xxx series wrought Al alloys

Secondary intermetallic phase formation during directional solidification of two 6xxx series wrought Al alloys at low growth velocities of 5–30 mm/min has been investigated using differential scanning calorimetry, transmission electron microscopy and scanning transmission electron microscopy. Thermodynamic calculations predict that a quasi-peritectic reaction, L+Al₁₃Fe₄ → α-Al+α-AlFeSi, should occur during equilibrium solidification of the alloys. However, no composite Al₁₃Fe₄/α-AlFeSi particles, but composite Al₁₃Fe₄/β-AlFeSi particles and triple phase junctions have been observed for the first time, indicating a divorced metastable β-AlFeSi quasi-peritectic reaction, L+Al₁₃Fe₄ → α-Al+β-AlFeSi. More detailed analysis suggests that the metastable β-AlFeSi quasi-peritectic reaction is more favourable both at nucleation and during growth. No unique orientation relationship was found between primary Al₁₃Fe₄ and peritectic β-AlFeSi. The nucleation and growth of peritectic phases and the morphology evolution of the two intermetallic phases, Al₁₃Fe₄ and β-AlFeSi, are discussed.     

复合添加Zr、Cr和Pr对Al-Zn-Mg-Cu合金组织和性能的影响

采用铸锭冶金法制备Al-Zn-Mg-Cu-Zr、Al-Zn-Mg-Cu-Cr-Pr和Al-Zn-Mg-Cu-Zr-Cr-Pr3种合金,通过金相显微、扫描电镜和透射电镜观察以及拉伸性能、极化曲线、应力腐蚀和剥落性能的测试,研究复合添加Zr、Cr和Pr对Al-Zn-Mg-Cu合金组织和性能的影响。结果表明:复合添加Zr、Cr和Pr可有效抑制Al-Zn-Mg-Cu合金回复过程中亚晶的合并和长大,显著抑制再结晶,提高合金抗应力腐蚀和抗剥落腐蚀的性能;与单独添加Zr的合金相比,复合添加Zr、Cr和Pr的合金断裂韧性KⅠC从23.3MPa·m1/2提高到29.3MPa·m1/2,合金应力腐蚀开裂界限应力强度因子KⅠSCC由10.9MPa·m1/2提高到24.5MPa·m1/2,合金的抗拉强度、屈服强度及伸长率都略有提高。     

Mn和Cr对Al-Mg-Si-Cu合金组织及性能的影响

通过金相观察、拉伸性能测试、X射线衍射、扫描电镜及能谱分析,研究了Mn、Cr对Al-Mg-Si-Cu铝合金微观组织及拉伸性能的影响。结果表明：添加Mn和Cr均能促进Al-Mg-Si-Cu合金铸锭形成粗大结晶相化合物,并且添加Mn的合金中形成的结晶相更多;均匀化过程中Mn和Cr均能促进结晶相由Al5FeSi型向Al8Fe2Si型转变,并且同时添加Mn和Cr的促进作用更加显著;添加Mn、Cr均能抑制变形晶粒在固溶处理时发生再结晶和晶粒长大,并且由单独添加Cr、单独添加Mn到同时添加Mn和Cr,抑制作用逐渐增强;添加Cr对合金强化作用有限,而添加Mn能显著提高合金强度。     

The grain refinement mechanism of cast aluminium by zirconium

The mechanism underlying the grain refinement of cast aluminium by zirconium has been studied through examination of a range of Al alloys with increasing Zr contents. Pro-peritectic Al₃Zr particles are reproducibly identified at or near the grain centres in grain-refined alloy samples based on the observations of optical microscopy, scanning electron microscopy and X-ray diffraction. From the crystallographic study using the edge-to-edge matching model, electron backscatter diffraction and transmission electron microscopy, it is substantiated that the Al₃Zr particles are highly potent nucleants for Al. In addition, the effects of Al₃Zr particle size and distribution on grain refinement has also been investigated. It has been found that the active Al₃Zr particles are bigger than previously reported other types of active particles, such as TiB₂ for heterogeneous nucleation in Al alloys. Considering the low growth restriction effect of Zr in Al (the maximum Q-value of Zr in Al is 1.0 K), it is suggested that the significant grain refinement of Al resulting from the addition of Zr can be mainly attributed to the heterogeneous nucleation facilitated by the in situ formed Al₃Zr particles.     

Elemental and phase composition,morphology, and chemical features of the surface of Al–Ni Alloys in contact with liquid Ga–In eutectic

A set of aluminum–nickel alloys has been studied. The elemental composition of the samples has been determined by atomic emission and atomic absorption spectrometry. X-ray diffraction analysis has revealed that the alloying of the metals leads to the formation of Al₃Ni and Al₃Ni₂ intermetallic compounds, while a portion of Al remains in a metallic phase. The local chemical composition and surface morphology of the original alloys and the alloys activated with the liquid Ga–In eutectic have been studied by scanning electron microscopy and X-ray microanalysis. It has been shown that the original alloys are characterized by a pronounced morphological heterogeneity of interfacial regions in the near-surface layers. It has been found that the studied Al–Ni alloys are activated by the liquid Ga–In eutectic; however, one of the alloy components—the Al₃Ni intermetallic compound—does not undergo significant morphological and chemical changes in contact with the liquid eutectic.     

Contributions of phase and structural transformations in multicomponent Al-Mg alloys to the linear and nonlinear mechanisms of anelasticity

The effects of the processes of severe plastic deformation (SPD), recrystallization, and precipitation of the β phase in multicomponent alloys of the Al-5Mg-Mn-Cr and Al-(4–5%)Mg-Mn-Zn-Sc systems on the mechanisms of grain-boundary relaxation and dislocation-induced microplasticity have been studied in some detail. To stabilize the ultrafine-grained structure and prevent grain growth, dispersed Al-transition-metal particles, such as Al₃Zr, Al₆Mn, Al₇Cr, Al₆(Mn,Cr), Al₁₈Cr₂Mg₃ have been used. We have special interest in alloys with additions of scandium, which forms compounds of the Al₃Sc type and favors the precipitation of finer particles compared to the aluminides of other transition metals. After SPD, Al-(4–5%)Mg-Mn-Zr-Sc alloys exhibit an enhanced recrystallization temperature. The general features of the dislocation and grain-boundary anelasticity that have been established for the binary Al-Mg alloys are retained; i.e., (1) the decrease in the dislocation density in the process of recrystallization of cold-worked alloys leads to the formation of a pseudo-peak in the curves of the temperature dependences of internal friction (TDIF) and to a decrease in the critical amplitude of deformation corresponding to the onset of dislocation motion in a stress field; (2) the precipitation of the β phase suppresses the grain-boundary relaxation; (3) the dissolution of the β phase, the passage of the magnesium atoms into the solid solution, and the precipitation of the β’ phase upon heating hinder the motion of dislocations; (4) the coarsening of the highly dispersed particles containing Zr and Sc increases the dislocation mobility. The grain-boundary relaxation and dislocation-impurity interaction and their temperature dependences, as well as processes of the additional alloying of the binary alloys by Mn, Cr, Zr, and Sc, have been estimated quantitatively.     

Cu 含量对Al-Zn-Mg-Cu合金的组织性能和断裂行为的影响

介绍了Cu含量对Al-Zn-Mg-Cu合金组织性能和断裂行为的影响。利用光学显微镜、扫描电镜、X射线衍射等方法对合金的组织和断口进行了分析。结果表明,Cu含量对合金中粗大金属间化合物的类型和含量有较大的影响。含w（Cu）=2．3％的高Cu的Al-Zn-Mg-Cu合金中粗大金属间化合物较多,Al2CuMg较多。过时效状态下,高Cu的Al-Zn-Mg-Cu合金断口以粗大的Al2CuMg粒子开裂的韧窝为主;含w（Cu）=1．7％的低Cu合金断口以晶粒内小的穿晶韧窝为主。高Cu的Al-Zn-Mg-Cu合金中粗大的Al2CuMg粒子消耗了大量的Cu,降低了合金强化的潜力,在过时效状态下促进合金开裂。     

Development of a nanostructured Zr3Co intermetallic getter powder with enhanced pumping characteristics

Nanostructured Zr₃Co intermetallic powders were produced by mechanical alloying (MA) of the elemental Zr and Co powders. The phase evolution, microstructural characteristics and formation mechanism of Zr₃Co powders during mechanical alloying were studied by means of X-ray diffraction method, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The results showed that after an optimum mechanical alloying time and optimum heat treatment, nanostructured Zr₃Co intermetallic powder was achieved. It was found that Zr₃Co intermetallic compound is formed by the diffusion of Cobalt into Zirconium during mechanical alloying. In the second stage, after an optimum heat treatment, formation and growth of Zr₃Co intermetallic compound are controlled by interdiffusion of Co and Zr. Moreover, our results indicated that the synthesized nanostructured Zr₃Co intermetallic powders show enhanced pumping properties and gas sorption response in contrast to the bulk, thin film and commercial getters.     

Effects of minor Sc and Zr additions on mechanical properties and microstructure evolution of Al−Zn−Mg−Cu alloys

The effects of minor Sc and Zr additions on the mechanical properties and microstructure evolution of Al−Zn−Mg−Cu alloys were studied using tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ultimate tensile strength of the peak-aged Al−Zn−Mg−Cu alloy is improved by about 105 MPa with the addition of 0.10% Zr. An increase of about 133 MPa is observed with the joint addition of 0.07% Sc and 0.07% Zr. For the alloys modified with the minor addition of Sc and Zr (0.14%), the main strengthening mechanisms of minor addition of Sc and Zr are fine-grain strengthening, sub-structure strengthening and the Orowan strengthening mechanism produced by the Al₃(Sc,Zr) and Al₃Zr dispersoids. The volume of Al₃Zr particles is less than that of Al₃(Sc,Zr) particles, but the distribution of Al₃(Sc,Zr) particles is more dispersed throughout the matrix leading to pinning the dislocations motion and restraining the recrystallization more effectively.     

Localized dissolution initiated at single and clustered intermetallic particles during immersion of Al–Cu–Mg alloy in sodium chloride solution

Aiming at understanding how intermetallic phases response when AA2024-T3 aluminium alloy is exposed to chloride-containing aqueous medium, scanning electron microscopy was employed to provide morphological information on alloy surface before and after corrosion testing. Energy dispersive X-ray spectroscopy was carried out to determine compositional change in intermetallic particles. Atomic force microscopy was used to examine topographical variation introduced by the reactions of intermetallic phases. Transmission electron microscopy combined with ultramicrotomy was carried out on dealloyed Al₂CuMg particles and their periphery region. It is found that dealloyed Al₂CuMg particles exhibited porous, polycrystalline structure comprised of body-centred cubic copper particles with sizes of 5 to 20 nm. Aluminium matrix started to trench in the periphery of Al₂CuMg particles at the early stage of dealloying. Development of trenching in Al–Cu–Fe–Mn–(Si) particle's periphery was not uniform and took longer time to initiate than Al₂CuMg dealloying. Localized corrosion at a cluster of Al₂CuMg and Al₂Cu particles was mainly associated with Al₂CuMg particles.     

Effects of Zr additions on structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti (wt.%) alloy

The effects of different Zr additions(0.05wt.%-0.5wt.%)on the structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti(wt.%)alloy solidified under a high cooling rate(18℃·s^-1),in as-cast and T6 heat-treated conditions were studied.The as-cast structure of the alloy consists of equiaxed grains ofα-Al with an average size of 64μm which is unaffected by the Zr additions,indicating the ineffectiveness of Zr in the grain refinement of the alloy.Scanning electron microscopy,along with X-ray diffraction analysis revealed the presence of elongatedθ-Al2Cu at the grain boundaries;in addition,coarse Al3Zr particles exist in the intergranular regions of the 0.5wt.%Zr-containing alloy.After the T6 heat treatment,the elongatedθparticles were fragmented;however,the coarse Al3Zr particles remained unchanged in the microstructure.Also,the formation of fineβ’-Al3Zr andθ’’-Al3Cu/θ’-Al2Cu phases during T6 heat treatment was revealed by transmission electron microscopy.The results of the tensile tests showed that the Zr additions increase the strength of the alloy in both as-cast and T6 heat-treated conditions,but reduce its elongation,especially with 0.5wt.%Zr addition.The 0.3wt.%Zr-added alloy in the T6 heat-treated condition has the highest quality index value(249 MPa).Fractography of the fracture surfaces of the alloys revealed ductile fracture mode including dimples and cracked intermetallic phases in both conditions.     

DSC Study on Phase Transitions and Their Correlation with Properties of Overaged Al-Zn-Mg-Cu Alloys

This article investigates the phase transitions of complex quaternary Al-Zn-Mg-Cu alloys with Zr addition at overaged conditions. Differential scanning calorimetry (DSC) is employed to quantitatively analyze the phase transformation phenomena of a wide range of 7xxx series alloys through endothermic and exothermic reactions. The DSC observations detailing heat effect peaks and thermal parameters of ??? dissolution contain valuable information on the presence of equilibrium phases and the optimum alloying element contents. Based on DSC experimental data and phase diagrams, the balance of critical properties such as strength and electrical conductivity of Al-Zn-Cu-Mg 7xxx series alloys has been studied by considering the formation, dissolution, and incipient melting of S and T phase, dissolution of ??? phase as well as the formation of ?? phase. Nine Al-Zn-Mg-Cu alloys have been studied through microstructural examination and detailed DSC analysis. The correlation between the properties and the DSC data of the selected alloys has been analyzed.     

Evolution of eutectic structures in Al-Zn-Mg-Cu alloys during heat treatment

1 Introduction The solute redistribution during solidification leads to microsegregation and the formation of coarse intermetallic particles, which can significantly influence the properties and productivity of the 7000 series aluminium alloys[1]. In ord…     

Hydrogen accommodation in Zr second phase particles: Implications for H pick-up and hydriding of Zircaloy-2 and Zircaloy-4

Ab-initio computer simulations have been used to predict the energies associated with the accommodation of H atoms at interstitial sites in α, β-Zr and Zr–M intermetallics formed with common alloying additions (M = Cr, Fe, Ni). Intermetallics that relate to the Zr₂(Ni,Fe) second phase particles (SPPs) found in Zircaloy-2 exhibit favourable solution enthalpies for H. The intermetallic phases that relate to the Zr(Cr,Fe)₂ SPPs, found predominantly in Zircaloy-4, do not offer favourable sites for interstitial H. It is proposed that Zr(Cr,Fe)₂ particles may act as bridges for the migration of H through the oxide layer, whilst the Zr₂(Ni,Fe)-type particles will trap the migrating H until these are dissolved or fully oxidised.     

Effect of hydrogen on the formation of the structure and phase composition in the Ti2AlNb-based alloy

Methods of X-ray diffraction, electron microprobe analysis, electron microscopy, differential thermal analysis, and microdurometry were used to study the effect of alloying with 5.2 and 8.5 at % hydrogen on the occurrence of phase and structural transformations in the intermetallic alloy Ti—24.3 Al—24.8 Nb—1.0 Zr—1.4 V—0.6 Mo—0.3 Si (at %) upon heating in the temperature range of 700-1050°C. It has been established that hydrogen favors the stabilization of the ? solid solution, the suppression of the formation of the α ₂ phase, and the reduction of the temperature of heating for quenching, starting with which the formation of an ordered a phase is possible in the alloy structure. Procedures of calculation of the electron concentration in the alloys with hydrogen have been proposed. By the method of the differential scanning calorimetry, the temperatures of disordering have been determined in the alloys.     

Analysis of phase in Cu–15%Cr–0.24%Zr alloy

The vacuum medium-frequency induction melting technology was employed to prepare the Cu–15%Cr–0.24%Zr alloy. The scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to analyze the phase composition, morphology and structure of the alloy. The results reveal that the as-cast structure of the alloy consists of Cu matrix, Cr dendrite, eutectic Cr and Zr-rich phase. A large number of Cr-precipitated phases occur in the Cu matrix, and Cu₅Zr particles can be found in the grain boundary of Cu matrix. The HRTEM images prove that there is a semi-coherent relationship between Cu₅Zr and Cu matrix.