Influence of main components and transition metals on the structure and properties of melt-quenched high-strength aluminum alloys of the Al-Zn-Mg-Cu system

The application of melt quenching for the production of high-strength heat-treatable Al-Zn-Mg-Cu aluminum alloys is considered. The complex multifactor mechanism of hardening of these materials is explained on the basis of their structure and mechanical properties, and a quantitative estimation of individual hardening factors is presented. The influence of the main alloy components on the phase composition, structure and properties of the alloys has been analyzed, and the ultimate total contents of the components and their weight ratio that ensure the optimal set of properties are determined. In addition, the advantage of complex allying of these alloys with various groups of transition metals is established. The possibility of implementation of these approaches is illustrated by the example of production of high-strength melt-quenched Al-Zn-Mg-Cu alloys.     

Thermomechanical treatments on high strength Al-Zn-Mg(-Cu) alloys

An investigation was carried out to determine the metallurgical properties of Al-Zn-Mg and Al-Zn-Mg-Cu alloy products processed according to newly developed Final Thermomechanical Treatments (FTMT) of T-AHA type. The results show that these cycles can be utilized to produce wrought products of high purity Al-Zn-Mg(-Cu) alloys characterized by equivalent toughness and ductility and much higher strength than conventionally processed commercial purity materials. Based on transmission electron microscopy studies, it was found that such improved behavior of FTMT material is attributable to the superposition of hardening effects, from aging precipitation and from dislocations. Preliminary stress-corrosion and fatigue tests indicate that these properties are not substantially influenced by T-AHA thermomechanical process. Further work is needed in this area, in order to better understand the directions to follow for developing better alloys.     

Effect of Zn Content on the Microstructure and Properties of Super-High Strength Al-Zn-Mg-Cu Alloys

The microstructure and properties of three different Al-Zn-Mg-Cu alloys with high Zn content (9 wt pct, 10 wt pct, and 11 wt pct, marked as 9Zn, 10Zn, and 11Zn, respectively) were investigated. The strength of alloys increases as the Zn content increases from 9 wt pct to 10 wt pct, while it does not increase any more as the Zn content increases continuously from 10 wt pct to 11 wt pct. The stress-corrosion cracking (SCC) resistance decreases as the Zn content increases from 9 wt pct to 10 wt pct, while it changes unobviously as the Zn content increases continuously from 10 wt pct to 11 wt pct. The elongation and fracture toughness of alloys decrease as the Zn content increases in these Al-Zn-Mg-Cu alloys. The Zn content has little effect on the precipitation reaction of Al-Zn-Mg-Cu alloys that contain the mixture of GP zones, and η′ are the main Matrix Precipitates (MPt) in the peak-aging state, and the mixture of η′ and η are the main MPt in the over-aging state. The amount of MPt and coarse T (AlZnMgCu) phases are shown to increase with the increasing Zn content in Al-Zn-Mg-Cu alloys. The coarse T phases hardly dissolve into the matrix and are the source for the crack initiation, which may be the responsibility for the negative effect on the properties of high Zn content Al-Zn-Mg-Cu alloys.     

含铒先进铝合金

综述了Er在高纯铝、Al-Mg,Al-Zn-Mg,Al-Li以及Al-Cu合金中的作用情况,分析讨论了Er在铝及其合金中的作用机制。结果表明:对于高纯铝、Al-Mg,Al-Zn-Mg,Al-Li合金来说,适量Er可以显著细化合金铸态晶粒,能够在一定程度上抑制再结晶,提高合金热稳定性,与此同时可以提高不同热处理状态下的合金的拉伸强度与硬度,Er的细化及强化作用主要与Al3Er相的形成有关;对于Al-Cu合金,Er能够细化枝晶网胞组织,提高再结晶温度,然而对合金的力学性能并无益处。     

The influence of alloying on the microstructure and mechanical properties of P/M Ni3Al

The influence of alloying additions of iron and chromium alone and in combination with molybdenum and zirconium on the heat treatment response and mechanical properties of powder metallurgy processed Ni₃Al based materials have been characterized. Additions of 8 at.% Cr result in considerable solid solution strengthening, while 11 at.% Fe by itself has little effect on the yield strength. Additions of both iron and chromium result in an alloy with higher strength than either unalloyed Ni₃Al or alloys with either element alone, however, the ductility is reduced by formation of β′ phase. The alloys containing Fe or Cr alone and the unalloyed material are essentially single phase γ′ after heat treating at 1000°C for 1 h, while the more complex alloys have a significant volume fraction of disordered γ phase. The alloys with a high degree of order exhibit large yield drops and corresponding Lüders strains. As the amount of disorder increases the magnitude of both the yield drop and Lüders strain decreases. Values of the power law hardening exponent for the alloys are found to be as high as 0.8 and generally decrease as the amount of γ phase increases as a result of alloying. All of the materials have high strain rate sensitivity at elevated temperature combined with resistance to grain growth that suggests they will deform superplastically.     

Diamond cutting tools with a Ni<Subscript>3</Subscript>Al matrix processed by reaction pseudo-hipping

Nickel aluminide, Ni₃Al, has high hot strength, which could help overcome the high heat and the interrupted vibrations that diamond cutting tools encounter during operation. Reaction pseudo-hipping, on the other hand, require only a short dwell time at high temperatures, which are detrimental to the diamond grits. Thus, it is promising to combine the unique nickel aluminide with the unique reaction pseudo-hipping process and replace the commonly used cobalt matrix. This study reports for the first time the process and application of reaction-pseudo-hipped Ni₃Al matrix for diamond tools. In this work, mixtures of elemental nickel, aluminum, boron powder, and diamond particles are reaction-pseudo-hipped. Densities greater than 99 pct and mechanical properties comparable to those of the cobalt are attained. With high-grade diamond grits, the tools thus prepared show, under dry cutting conditions, a grinding ratio 118 pct higher than that with the cobalt matrix.     

The eutectoid region of the Zr−Ga system

The zirconium-rich portion of the Zr?Ga phase diagram was determined by the optical examination of microstructures of isothermally annealed and quenched alloys. A deviation from binary equilibrium, was observed even though careful selection of materials and techniques held impurities to a minimum and produced alloys with a purity of at least 99.9 pct. The slopes of the α-β boundaries are depressed and the range of solubility of the solid solution phases is restricted when compared to the phase diagrams of other Group IIIB elements, apparently as a result of the large difference in atomic size between zirconium and gallium. Thea ₀ andc ₀ lattice constants of cph zirconium are contracted and the axial ratio is expanded by the addition of gallium. The change inc/a at 1 at. pct was very close to the change observed in Zr-In alloys, in agreement with general dependence of these properties in zirconium alloys upon electron to atom ratio. A eutectoid reaction occurs at 860°C with β solid solution (1.8 at. pct Ga) decomposing into α solid solution (0.8 at. pct Ga) and Zr₃Ga. Cast microstructures suggest a eutectic reaction in which liquid (21.0 at. pct Ga) decomposes into β (8.0 at. pct Ga) and Zr₅Ga₃. It is proposed that intermediate phases are formed at 25.0 at. pct Ga (Zr₃Ga), 37.5 at. pct Ga (Zr₅Ga₃), and 50.0 at. pct Ga (ZrGa) although the exact composition was not determined.     

Comparison of the influence of chromium and zirconium on the quench sensitivity of Al-Zn-Mg-Cu alloys

The role played by small additions of chromium and zirconium on the “quench-sensitivity” of Al-Zn-Mg-Cu high purity alloys has been studied. The effects of the quench rate reduction have been evaluated by mechanical testing; the associated microstructural features have been investigated by electron microscopy. The obtained data adequately explain the mechanisms of the “quench-sensitivity”.     

Effect of Cobalt on Phase Formation, Microstructure, and Mechanical Properties of Cu50?xCoxZr50 (x?=?2, 5, 10, 20?at.?pct) Alloys

In this work, the effect of cobalt on the phase formation and mechanical properties of rapidly solidified Cu_50?xCo_xZr₅₀ (x?=?2, 5, 10, and 20?at.?pct) alloys was investigated. CuZr martensite forms in the case of low Co contents (x?=?2 and 5?at.?pct), while in the alloys with 10 and 20?at.?pct Co, the B2 phase is stable even at room temperature. The deformation behavior of the rods under compressive loading depends strongly on the microstructure and, thus, on the alloy composition. Cobalt affects the fracture strength of the as-cast samples, and deformation is accompanied by two yield stresses for high Co-content alloys, which undergo deformation-induced martensitic transformation.     

Erosion-resistant coatings for gas turbine compressor blades

The effect of ion-plasma coatings made from high-hardness metal compounds on the erosion and corrosion resistance and the mechanical properties of alloy (substrate) + coating compositions is comprehensively studied. The effects of the thickness, composition, deposition conditions, and design of coatings based on metal nitrides and carbides on the relative gas-abrasive wear of alloy + coating compositions in a gas-abrasive flux are analyzed. The flux contains quartz sand with an average fraction of 300–350 μm; the abrasive feed rate is 200 g/min; and the angles of flux incidence are 20° (tangential flow) and 70° (near-head-on attack flow). Alloy + coating compositions based on VN, VC, Cr₃C₂, ZrN, and TiN coatings 15–30 μ m thick or more are shown to have high erosion resistance. A detailed examination of the coatings with high erosion resistance demonstrates that a zirconium nitride coating is most appropriate for protecting gas turbine compressor blades made of titanium alloys; this coating does not decrease the fatigue strength of these alloys. A chromium carbide coating is the best coating for protecting compressor steel blades.     

Effect of additions of zirconium,chromium, and nickel on the structure and characteristics of superplasticity of alloys of the Al-Zn-Mg-Cu system

By optical and transmission microscopy as well as by X-ray structural analysis, the structure and properties of alloys of the Al-Zn-Mg-Cu system with Ni, Zr, and Cr additions during superplastic deformation are investigated. It is shown that introduction of 0.26% Zr into the alloys leads to the formation of a nonrecrystallized or partially recrystallized structure in the billets. Such materials manifest the effect of superplasticity at t = 515°C in a range of deformation rates of (0.15–1.0) × 10^?2 s^?1, and the relative elongation reaches 450–680%.     

Solid solution decomposition mechanisms in cast and microcrystalline Al-Sc alloys: I. Experimental studies

The structure and the electrical and mechanical properties of Al-Mg-0.22 wt % Sc-0.15 wt % Zr alloys with various magnesium contents (0, 1.5, 4.5 wt %) are experimentally studied during the decomposition of the solid solution of scandium and zirconium in the states after solidification from a melt (cast ingots) and after subsequent multicycle equal-channel angular pressing (microcrystalline structure). The dependences of electrical resistivity ??, microhardness HV, macroelasticity limit ??₀, and yield strength ??_y on the annealing temperature and time are analyzed.     

THE PREPARATION AND PROPERTIES OF COPPER,NICKEL, AND IRON CONTAINING A DISPERSED OXIDE PHASE

Abstract

Three methods are described for the preparation of a stable oxide in copper, nickel, or iron. The first, which has been applied to all three metals, requires a reaction between the matrix metal oxide and the refractory oxide at high temperatures such that subsequent reduction will yield a dispersion of oxide in the matrix metal powder. In the second method, copper hydroxide or carbonate is precipitated in the presence of an aluminium salt. Ignition of the precipitate to the oxide followed by hydrogen reduction gives a copper powder containing a dispersion of alumina. In the third process, a salt that can be decomposed to a stable oxide is dissolved in molten nickel nitrate, which on rapid cooling eitherretains the additive in solid solution or as an intimate dispersion. Nickel powder containing the dispersed oxide is obtained on subsequent decomposition.

The results on sintered and worked materials show a substantial improvement in mechanical properties compared with the pure metals. Improvements are also achieved in the sintered nickel alloys, which can be sintered to high densities. The effect of the dispersion on the structure and recrystallization behaviour of these materials is discussed.     

Effects of B,C, and Zr on the structure and properties of a P/M nickel base superalloy

The boron and carbon levels of a P/M nickel base superalloy were systematically varied in order to determine the mechanisms by which these elements strengthen the alloy, and their optimum concentration. Carbon levels were reduced to 20 ppm while the boron level was varied from 0.02 to 0.10 wt pct. Carbon levels of 0.002 and 0.05 wt pct were also studied, while maintaining a boron concentration of 0.02 wt pct. Zirconium levels were maintained at 0.06 wt pct. The resulting alloys were subjected to identical heat treatments and examinedvia SEM, TEM, and STEM microscopy. The alloys were also subjected to tensile, creep, stress-rupture, and fatigue crack growth tests. Results show that both carbon and boron have a strong influence on the formation of grain boundary precipitates, as expected. Carbon was present as the MC and M₂₃C₆ type carbides, while boron combined to form an intergranular M₃B₂ boride. Boron and zirconium were observed to be critical to the alloys' mechanical properties, although boron levels above the solubility limit resulted in no further improvement or debit in strength. Carbon additions resulted in no improvement in properties, indicating the feasibility of a carbon-free P/M superalloy. The role of the minor element additions is discussed in terms of both microstructural features and related strengthening mechanisms.     

Grain boundary ductile fracture in precipitation hardened aluminum alloys

Published microstructural studies of grain boundary (gb) fracture in precipitation hardened aluminum alloys are reviewed with respect to the three main ideas that have been developed to explain the gb fracture surfaces. The ideas are

• 1.(1) microvoid growth at large gb precipitates,
• 2.(2) strain localization in the soft, and sometimes solute-free, gb precipitate free zones (pfz) and
• 3.(3) the influence of matrix precipitate shear giving rise to inhomogeneous “planar” slip that may apply large stress concentrations to the gb at the end of slip bands. Although the last two processes have a supporting role in many cases, the published evidence strongly suggests that the first process is of overwhelming importance. This conclusion has been tested by reversion experiments in model Al-Li alloys in which microstructures with increasing area fractions, A_f, of large stable δ precipitates (Al-Li) were produced, but with equivalent matrix structures and yield strengths. The materials show marked falls of toughness and of fracture strain as A_f was increased. Studies of surface slip markings in the Al-Li alloys suggested that slip was initiated at the large gb δ precipitates. Only very limited evidence for a role of planar slip in the fracture of the Al-Li alloys was found in contrast to observations on high purity Al-Zn-Mg-Cu alloys where planar slip seemed to show more importance. Brief studies on a nickel based alloy, MAR-M200, suggested that even in the absence of a pfz, strong room temperature embrittlement by gb precipitates was produced. The results of this study suggest that the marked problems of gb fracture in Al-Li alloys are associated with large gb δ precipitates. Jensrud and Ryum [Mater. Sci. Engng64, 229 (1984)] have shown how gb precipitate growth is facilitated in this system as the gb δ phase is very much less soluble than the strengthening δ′ (Al₃Li) phase.

     

Solvent extraction of nickel and cobalt by mixtures of carboxylic acids and non-chelating oximes

The effect of non-chelating oximes on the solvent extraction of nickel(II) and cobalt(II) by solutions of carboxylic acids (H₂A₂) in xylene has been studied. Synergistic enhancements of extraction were found with aldoximes, but not with ketoximes. The synergistic effects are larger for nickel than for cobalt, with the result that the selectivities of the carboxylic acids for nickel over cobalt are considerably enhanced in the presence of aldoximes. The influence of the molecular structure of the oxime and carboxylic acid components upon the synergistic effects is rationalized in terms of the prevailing stereochemical and electronic effects. The extracted complexes were shown to be octahedral in structure, with the compositions NiA₂(oxime)₄ and CoA₂(oxime)₄.The mixed reagent systems may prove useful for the selective extraction of nickel in the presence of cobalt.     

Evolution of Intermetallics,Dispersoids, and Elevated Temperature Properties at Various Fe Contents in Al-Mn-Mg 3004 Alloys

Nowadays, great interests are rising on aluminum alloys for the applications at elevated temperature, driven by the automotive and aerospace industries requiring high strength, light weight, and low-cost engineering materials. As one of the most promising candidates, Al-Mn-Mg 3004 alloys have been found to possess considerably high mechanical properties and creep resistance at elevated temperature resulted from the precipitation of a large number of thermally stable dispersoids during heat treatment. In present work, the effect of Fe contents on the evolution of microstructure as well as high-temperature properties of 3004 alloys has been investigated. Results show that the dominant intermetallic changes from α-Al(MnFe)Si at 0.1 wt pct Fe to Al₆(MnFe) at both 0.3 and 0.6 wt pct Fe. In the Fe range of 0.1–0.6 wt pct studied, a significant improvement on mechanical properties at elevated temperature has been observed due to the precipitation of dispersoids, and the best combination of yield strength and creep resistance at 573 K (300 °C) is obtained in the 0.3 wt pct Fe alloy with the finest size and highest volume fraction of dispersoids. The superior properties obtained at 573 K (300 °C) make 3004 alloys more promising for high-temperature applications. The relationship between the Fe content and the dispersoid precipitation as well as the materials properties has been discussed.     

Effect of alloying elements on the microstructure and properties of a hot-rolled low-carbon low-alloy bainitic steel

A two-level full factorial statistical experiment consisting of eight alloys was conducted to determine the effect of 2 pct cobalt, 1 pct nickel and 1 pct chromium on the hot-rolled microstructure and properties of a bainitic steel containing 0.2 pct C, 2 pct Mn, 1 pct Si, 0.75 pct Mo and 0.003 pct B. The results indicate that chromium induced the formation of the acicular bainitic structure while cobalt favored massive ferrite formation and resulted in islands of martensite and/or austenite. Nickel, when added singly, did not appear to influence the microstructure but in combination with chromium, enhanced the formation of the lower bainitic structure. The mechanical properties were statistically analyzed and statistical equations were obtained to predict optimized compositions. These equations indicate that chromium increased the toughness of these steels more than nickel. However, it was shown that with similar bainitic structures, nickel enhanced the toughness more than chromium. The results illustrate the short-coming of a pure statistical approach to the design of alloys.     

Effect of alloying elements on the microstructure and properties of a hot-rolled low-carbon low-alloy bainitic steel

A two-level full factorial statistical experiment consisting of eight alloys was conducted to determine the effect of 2 pct cobalt, 1 pct nickel and 1 pct chromium on the hot-rolled microstructure and properties of a bainitic steel containing 0.2 pct C, 2 pct Mn, 1 pct Si, 0.75 pct Mo and 0.003 pct B. The results indicate that chromium induced the formation of the acicular bainitic structure while cobalt favored massive ferrite formation and resulted in islands of martensite and/or austenite. Nickel, when added singly, did not appear to influence the microstructure but in combination with chromium, enhanced the formation of the lower bainitic structure. The mechanical properties were statistically analyzed and statistical equations were obtained to predict optimized compositions. These equations indicate that chromium increased the toughness of these steels more than nickel. However, it was shown that with similar bainitic structures, nickel enhanced the toughness more than chromium. The results illustrate the short-coming of a pure statistical approach to the design of alloys.