Mn Zr Alloys Research Articles

New insight into enhancing the comprehensive mechanical performance in non-stretched Al-Cu-Li-(Mg)-(Ag)-Mn-Zr alloys

Wrought Al-Cu-Li alloys usually necessitate pre-stretching to improve their mechanical properties. A novel insight into enhancing the mechanical properties of a non-stretched Al-Cu-Li alloy has been proposed by optimizing the Ag/Mg ratios and investigating their impact on precipitation behavior. Four alloys having Ag/Mg ratio between 0.24–5.63 and a combined Ag + Mg content of 1.1 wt% were designed. The results indicated that the strengthening precipitates were mainly plate-like T1 and θ́ precipitates. With decreasing Ag/Mg ratios from 5.63 to 1.87, T1 phase fraction increased from 28 % to 39 %, and the corresponding θ́ phase fraction reduced from 72 % to 61 %. Comparatively, S' phases dominated the microstructure while impeding the formation of θ' and T1 precipitates at Ag/Mg ratio was 0.24. The alloy at Ag/Mg ratio of 0.95 had optimum mechanical properties owing to T1, Ś, and θ́ phases uniform dispersion within the matrix, among which T1 had the highest volume fraction (48 %).

Deformation Behavior, Microstructure and Mechanical Properties of new Al–Cu–Yb(Gd)–Mg–Mn–Zr Alloys

Deformation Behavior, Microstructure and Mechanical Properties of new Al–Cu–Yb(Gd)–Mg–Mn–Zr Alloys

Achieving low activation energy and double-peak texture after hot deformation of Mg–Al–Zn–Ca–Mn–Zr alloy and enabling the strength and ductility

In this study, the hot-deformation behavior of a die-casted Mg–Al–Zn–Ca–Mn–Zr alloy was investigated in the temperature range of 548–673 K and the strain rate range of 0.0001–1 s−1. The constitutive equation and processing maps were also developed to describe the flow stress behavior. The numerical simulation result revealed an average activation energy of ∼139.4 kJ mol−1, which is lower than the previously reported AZ31 Mg alloys. Subsequently, the low activation energy imparted a high degree of dynamic recrystallization and was mainly attributed to alloying elements Ca, Mn, and Zr. For optimum hot working parameters, processing maps displayed two different domains, the temperature range of 573–673 K for a strain rate range of 0.001–0.01 s−1 with a peak efficiency of 33% and a temperature of 673 K at a high strain rate of 0.01 s−1 with a peak efficiency of 31%. The microstructure evolution confirmed the validity of parameters and revealed high dynamic recrystallization. The average grain size ∼21.1 μm, ∼15.4 μm, and ∼16.1 μm were achieved at temperatures of 573 K, 623 K, and 673 K under a strain rate of 0.001 s−1. The profuse grain refinement is attributed to the pronounced accumulation of dislocation on grain boundaries and on the eutectic phases. In addition, the morphology of the eutectic phases was broken with the increase in the strain rate and temperature. Thus, the α-Mg and eutectic phases bear the compressive stresses and promote the dynamic recrystallization activity. Last but not least, the double peak texture after hot deformation was developed, which is one of the engineers' main requirements for enhancing the Mg alloy's ductility. Based on the above discussion, the hot deformed specimens exhibited an ultimate compressive strength of ∼340 MPa and elongated to fracture >25%. Consequently, this study enables the understanding of the broad use of Mg–Zn–Al–Ca–Mn–Zr alloys for automobile applications.

The role of corrosion product layers in the pitting resistance of powder-processed Al–Cr–Co–Mn–Zr alloys containing icosahedral quasicrystalline dispersoids

The role of corrosion product layers in the pitting resistance of powder-processed Al–Cr–Co–Mn–Zr alloys containing icosahedral quasicrystalline dispersoids

Effect of grain-boundary θ-Al2Cu precipitates on tensile and compressive creep properties of cast Al–Cu–Mn–Zr alloys

Tensile and compressive creep tests were performed at 300 °C on high-temperature Al–Cu–Mn–Zr (ACMZ) alloys with 6 wt% Cu (6Cu) and 9 wt% Cu (9Cu) to evaluate the effect on creep properties of micron-size θ-Al2Cu intergranular precipitates. For compressive creep, the increased volume fraction of θ-precipitates at grain boundaries (from ∼0.7% in 6Cu to ∼ 6% in 9Cu) does not affect deformation rates across the investigated stress range of 15–110 MPa, consistent with creep being controlled by submicron θ′-Al2Cu precipitates within grains, whose size and fractions are the same in both alloys. In contrast, for tensile creep, 9Cu creeps faster than 6Cu at stresses above 20 MPa, and this difference increases with the stress level. This discrepancy between tensile and compressive creep behavior is explained by cavitation during tensile creep, which is favored by higher volume fraction and larger size of intergranular θ precipitates in 9Cu. Conversely, larger precipitates impede cavity linkage resulting in improved creep ductility of 9Cu as compared to 6Cu at 300 °C.

Grain Refinement Effect on the Hot-Tearing Resistance of Higher-Temperature Al–Cu–Mn–Zr Alloys

The hot-tearing resistance of Al-Cu-Mn-Zr (ACMZ) alloys was investigated as a step toward introducing these new cast alloys for severe duty, higher-temperature applications, such as cylinder heads for down-sized, turbocharged automotive engines. Alloy Cu compositions were varied from 5 to 8 wt.%. Targeted Ti levels were 0.02, 0.1, and 0.2 wt.% via additions of the Al–5Ti–1B master alloy. Hot-tearing resistance was assessed by visual examination and ranking of the cracking severity in a multi-arm permanent mold casting. It was found that at high impurity contents (Fe and Si of 0.2 wt.% each), the Al–Cu–Mn–Zr alloy with 4.95 wt.% Cu exhibited the poorest hot-tearing resistance, irrespective of the grain refining amount. Microstructural analysis indicated an effective reduction in the grain size, as the Ti additions were increased to 0.02 and 0.1 wt.% Ti via the Al–Ti–B grain refiner. The finest grain size was attained with a 0.1 wt.% Ti. Based on the hot-tearing evaluation, it was found that the additional grain refining via the Al–5Ti–1B master alloy at 0.1 wt.% Ti significantly reduces the hot-tearing susceptibility at Cu contents greater than 7.3 wt.% for ACMZ alloys with low Fe and Si. These findings indicate that the best hot-tearing resistance was observed at a grain refiner level of 0.1 wt.% Ti and high Cu content (greater than 7.3 wt.%). This study to indicates that these Al–Cu–Mn–Zr alloys, which possess excellent microstructural stability and mechanical properties at elevated temperatures, can also possess excellent hot-tearing resistance.

Effect of copper content on the tensile elongation of Al–Cu–Mn–Zr alloys: Experiments and finite element simulations

Microstructures of cast aluminum alloys used in automotive engine applications often consist of intermetallic particles that can impact the tensile elongation of these alloys. Here, we investigate the effect of intermetallic grain boundary particles on tensile elongation by fabricating a series of alloys with Cu content varying between 6.0 - 9.0 wt% in cast Al–Cu–Mn–Zr (ACMZ) type compositions. The tensile elongation of as-aged ACMZ alloys decreases monotonically with increase in Cu content. While the microstructure within the grains and yield stress of the alloy remains invariant with Cu content, the decrease in tensile elongation correlates well with increase in the size and volume fraction of grain boundary particles. Microstructural observations are combined with finite element simulations to explain the trend in tensile elongation with changing Cu content. Crack initiation is found to occur by brittle fracture of the grain boundary particles. Increase in particle size promotes crack initiation by reduction in size dependent particle fracture strength. Lower inter-particle spacing at higher particle volume fraction further facilitates crack initiation by increasing stress within the particles caused by the interaction between stress fields of neighboring particles. Increase in particle volume fraction also accelerates crack propagation through the formation of macro shear zones in the microstructure. The increase in Cu content of cast ACMZ alloys, therefore, decreases tensile elongation by promoting both crack initiation and crack propagation.

Mechanisms for stabilizing θ′(Al2Cu) precipitates at elevated temperatures investigated with phase field modeling

While most Al–Cu and Al–Si–Cu alloys strengthened by the metastable θ′ phase exhibit extensive microstructural degradation above 200 °C, recent experimental work has demonstrated that θ′ precipitates can be stabilized to 350 °C by microalloying additions of Mn and Zr, resulting in improved mechanical properties at elevated temperatures. The present work utilizes phase field modeling to study the relationship between microalloying solute elements and the coarsening resistance of θ′. Simulations are designed to parse out the relative influence of various stabilization mechanisms on microstructural evolution of θ′ precipitates at elevated temperatures. Specifically, a ternary alloying element is added to a virtual microstructure to study the operation and effectiveness of stabilization mechanisms including solute drag, diffusion barriers, interfacial energy reduction, and lattice strain modification. Simulation results are compared with atom probe tomography observations. The simulations rationalize experimental observations of microstructural evolution and solute segregation in Al–Cu–Mn–Zr alloys, and reveal the interlinked thermodynamic and kinetic mechanisms that determine the elevated temperature stability of θ′ precipitates.

The Fatigue Crack Propagation of Al–Mg–Mn–Zr Alloy with Erbium

This study investigated the fatigue crack propagation of Al–Mg–Mn–Zr alloys with erbium. The research found that in this alloy the crack propagation path prefers to extend along the grain boundary. If there are too many second phases or impurities in the gain boundary, the crack propagation will be influenced. The dispersed Al3(Er, Zr) precipitate in the alloy can act as a core of heterogeneous nucleation to attract Mg, Zn and Al element, and reduce the large brittle Al3Mg2second phase appear on the grain boundary, so the fatigue crack propagation rate can be slow down. In addition, these Al3(Er, Zr) precipitate can pin the dislocation in the alloy to reduce stress concentration at the grain boundary, so it also has some positive effect to the fatigue crack propagation.

Influence of Si and Fe on the distribution of intermetallic compounds in twin-roll cast Al–Mn–Zr alloys

The aim of the experiments was to study the influence of Si and Fe on size and formation of secondary phases and recrystallization behavior of Al–Mn–Zr alloys prepared by twin-roll casting (TRC) in the industrial conditions. Microstructure (grain structure, phase composition, particle analysis) of these alloys was characterized during downstream processing. Quantitative particle analysis was carried out on FEG–SEM micrographs at both high and low magnifications. The phases were examined by light metallography, energy dispersive X-ray spectroscopy (EDXS) and by means of electron back-scattering diffraction (EBSD) according to their crystallographic structure. The microstructure at the final gauge was also observed by transmission electron microscope (TEM). A relatively high (0.5 wt.%) Si content and low (0.2 wt.%) Fe content in one of the alloys resulted in balancing of nucleation and dissolution rate for small particles. Hence a higher density of small particles was stable during the downstream processing, and this alloy showed improved recrystallization resistance.

Microstructure and mechanical properties of Al–Cu–Mg–Mn–Zr alloy with trace amounts of Ag

The microstructure and mechanical properties of Al–Cu–Mg–(Ag)–Mn–Zr alloys were studied by means of tensile testing, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that small additions of Ag to Al–Cu–Mg–Mn–Zr alloy can accelerate the hardening effect of the aged alloy and reduce the time to peak-aged. The mechanical properties can be improved both at room temperature and at elevated temperatures, which is attributed to the fine and uniform plate-like Ω precipitates. Meanwhile the ductility of the studied alloys remains at relatively high level. The major strengthening phases of the Ag-free alloy are θ′ and less S′, while that of Al–Cu–Mg–Mn–Zr alloy containing trace amounts of Ag are Ω and less θ′.

The effect of erbium on the microstructure and mechanical properties of Al–Mg–Mn–Zr alloy

The influences of erbium (Er) on the microstructure and mechanical properties of Al–Mg–Mn–Zr alloys have been investigated. It has been found that about 0.2 wt.% Er can be dissolved in the matrix, excess Er atoms segregate at grain boundaries to form primary Al 3Er. Addition of 0.4 wt.% Er refines the grain size of the as-cast alloy due to the formation of primary Al 3Er. The solid solution decomposes to form a dispersion of secondary Al 3Er, with facets parallel to {1 0 0} and {1 1 0} planes, during homogenization at 470 °C. The secondary Al 3Er precipitates improve strength, especially the elevated temperature strength. The yield strength, at 150 °C, of the alloy with 0.2 wt.% Er is 50% higher than that of the Er-free alloy. The recrystallization temperature of the alloy with 0.4 wt.% Er is about 25 °C higher than that of the alloy without addition of Er.

The substitution effect of boron on reentrant behavior of rapidly solidified Fe–Mn–Zr alloys

We have studied the magnetic properties of boron-substituted amorphous reentrant Fe–Mn–Zr alloys. The magnetic characterization of a-Fe 82Mn 8− x B x Zr 10 (numbers indicate at.%) alloys has been done through the studies of thermal variation of magnetization, ac susceptibility and ferromagnetic resonance. Low-temperature spin freezing was observed at 54 K with large coercivity and low magnetic moment for a-Fe 82Mn 8Zr 10. The large coercivity at low temperatures and high freezing temperature for this sample is attributed to magnetic hardening. With an increase of the concentration of B, it is observed that the Curie temperature increases and the spin-glass-like transition observed at low temperature moves to lower temperatures and finally vanishes at x = 8 at.%. A single resonance peak in FMR spectrum was observed below T C and at least two distinct line shapes were observed well beyond the T C for two of the compositions, namely, x = 4 and 6. These observations could be qualitatively understood in terms of a finite spin clusters plus an infinite ferromagnetic matrix model. It can also be concluded that the magnetic disorder is reduced as boron concentration is increased.

Vacuum degassing behavior of rapidly solidified Al–Mn–Zr alloy powders

Gas desorption behavior and surface change characteristics of Al–Mn–Zr, Al–Mn, and Al–Zr alloy powders with heating in vacuo have been investigated by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) measurements. TPD measurements on powders exposed to humid air, dry air, and high purity argon gas were performed to determine the gas species evolved during degassing of Al alloy powders. The alloy composition and P/M processing atmosphere had a strong influence on degassing behavior. The surface oxides of Al alloy powders containing Mn and/or Zr were prone to hydration. Thus, the formation of fresh Al 2O 3 on the Al alloy powders occurred at low temperature during vacuum degassing by the reaction, Al + 3H 2O = Al 2O 3 + 3H 2. High-temperature XPS showed that decomposition of the hydroxide into oxide on the Al–Mn–Zr alloys occurred at 623 K.

Correction to scaling critical exponents and amplitudes for amorphous Fe–Mn–Zr alloys

Asymptotic and leading correction to scaling critical exponents and amplitudes have been determined for quenched amorphous Fe 90− y Mn y Zr 10 ( y=0–8) ferromagnets through an elaborate analysis of temperature dependence of spontaneous magnetization, zero-field susceptibility and low-field AC susceptibility data obtained in the asymptotic critical region. From this analysis, it is found that the values of the critical exponents and amplitudes do not depend on the alloy composition and are in good agreement with the values predicted for three-dimensional Heisenberg ferromagnet system. The observed experimental results are consistent with the concept of scaling in that the exponent equalities β= γ( δ−1) and α=2(1− β)− γ are obeyed to a high degree of accuracy. These results show that both amorphous and crystalline materials behave similarly in the critical region though amorphous alloys show a wide asymptotic critical region than the crystalline materials. The presence of disorder does not seem to have any influence on critical behavior of the system investigated in the present work.

Passivity and its breakdown on sputter-deposited amorphous Mn-Zr alloys in neutral chloride solutions

Amorphous Mn-Zr alloys were prepared by DC magnetron sputtering in a wide composition range. The electrochemical behavior in borate-boric acid solutions of pH 8.4 containing 0.01-1 M NaCl was investigated in combination with XPS analysis. All alloys were spontaneously passive. Their pitting potential increased with increasing zirconium content, and the alloys with 75–87 at.% zirconium possess higher pitting resistance than zirconium. The high passivating ability was attributed to the formation of a homogeneous double oxyhydroxide film composed of major Zr 4+ and minor Mn 2+. The formation of zirconium-enriched passive film results from preferential oxidation of zirconium with a consequent enrichment of manganese in the exterior of the underlying alloy surface. The formation of a zirconium oxyhydroxide film containing a few percent of manganese cations on zirconium-rich alloys is responsible for a significantly thinner film thickness and higher pitting resistance in comparison with zirconium.

Magnetic and electrical properties of several Mn-based amorphous alloys

Magnetic and electrical properties of amorphous Mn-Y, Mn-Zr, and Mn-Nb alloys have been investigated. All these alloys have a temperature-dependent susceptibility which is well fitted by a Curie-Weiss law. This implies the existence of localized magnetic moments associated with the Mn atoms. In addition, amorphous Mn-Y alloys exhibit spin-glass characteristics at low temperature. The experimental results of the electrical resistivity show that the temperature coefficient of resistivity (TCR) of both Mn-Y and Mn-Zr are negative, while Mn-Nb has a positive TCR. On the other hand, the resistivity-temperature curves of Mn-Zr and Mn-Nb have nearly the same tendency but are different from that of Mn-Y.

Precipitation of quasicrystalline phase in rapidly solidified AlMnZr alloys

It is well known that the limiting equilibrium concentration of manganese in aluminum can be extended markedly by rapid solidification. Various metastable precipitates have been also found in this alloy, namely G (2), G', G'',. In addition to these phases, others have reported recently the presence of a less stable phase, designated T, in Al-5 wt% Mn foils following short annealing periods. T phase is now of interest because of the striking resemblance of electron diffraction patterns to those obtained from a quasicrystalline phase having icosahedral point group symmetry, which is formed in the rapidly solidified Al-15approx. =35 wt% Mn alloys. In recent work on the precipitation characteristics of rapidly solidified Al-7 wt% Mn- 1 wt% Zr alloys, it has been shown that appreciable precipitation hardening takes place during annealing at temperatures between 350approx. =450/sup 0/C. In these cases, the Mn enhanced the precipitation hardening since the increase in hardening was about two times as much as that of the Al-1 wt% Zr alloys under the optimum conditions of temperature and Mn content. The results of X-ray diffraction analyses and TEM observations suggested that principal precipitate attributing to the hardening was a pseudomorphous phase of the equilibrium Al/sub 6/Mn. However,more » there remain to be explored many problems including more exact structural information about the phase. In the present paper the authors report preliminary studies of the structure of the precipitate phase and propose the age hardening of the Al-7 wt% Mn-1 wt% Zr alloys to be induced by the precipitate similar to a quasicrystalline phase that appears in rapidly solidified Al-Mn alloys containing a large amount of Mn. The study was mainly performed using conventional transmission electron microscopy and selected area diffraction.« less

Effect of d-band mixing in Mn-transition-metal spin glasses.

The recently reported magnetic properties of amorphous (a) Mn-Zr alloys exhibited two remarkable and unexpected results. First, while Ni, Co, and Fe display no local magnetic moment when alloyed with Zr in metallic glasses, Mn has a local moment in a--Mn-Zr. Second, the existence of the Mn local moment does not result in a spin-glass interaction. These results can be understood by the study of the magnetic properties of a--Cu-Zr-Mn alloys presented here which shows that the absence of spin-glass interaction in a--Mn-Zr is not due to the amorphous state but to a mixing of the Zr and Mn d bands. This explanation suggests that a spin-glass interaction should exist when the transition-metal host for Mn displays a low density of d states at the Fermi level (${E}_{F}$). Indeed, among transition metals, W has the lowest density of d states at ${E}_{F}$, and W-Mn alloys exhibit a spin-glass transition. The susceptibility of this new spin glass was measured in low ac field and in both low and high dc fields. The spin-freezing temperature (${T}_{\mathrm{SG}}$) increases essentially linearly with Mn content up to 34 at. % Mn where massive antiferromagnetism sets in.