Aluminum-based Solid Solution Research Articles

Application of microindentation to the evaluation of strain distribution over the section of extruded aluminum alloy bars

The paper proposes to supplement the monitoring of strain uniformity over the cross-section of extruded aluminum alloy bars, based on the macro- and microstructure in the central part, at ½ radius, and in the surface zone in several cross-sections along the length of press products, with microindentation of these sections. For this purpose, the microstructure, the loading diagram, and the pattern of the distribution of micromechanical properties across the cross-section of extruded bars made of the AD33 and D16 aluminum alloys are comparatively analyzed. These alloys differ in that in one alloy, AD33, the alloying elements strengthen the aluminum-based solid solution without forming independent phases, and in the other, D16, they form strengthening intermetallic compounds Al2CuMg. The microhardness of the AD33 alloy is ~55 HV 0.1, that of the D16 alloy being 120 HV 0.1. The alloys differ in the distribution of micromechanical properties over both the transverse and longitudinal sections of the extruded bars. It has been found that maximum homogeneity is characteristic of the central part of the rods made of both alloys. The microindentation data correlate with the changes in the microstructure and the results of assessing the distribution of microstrains in the crystal lattice of an aluminum-based solid solution over the cross-section of extruded products by EBSD using recrystallization maps. This makes it possible to recommend the microindentation method for assessing the distribution of strains over the cross-section of extruded aluminum alloy bars.

Precipitation Behavior of the Metastable Quasicrystalline I-Phase and θ′-Phase in Al-Cu-Mn Alloy

The precipitation behavior and mechanical properties for conventionally solidified Al-2.0wt.%Cu-2.0wt.%Mn alloy were studied. The supersaturated aluminum-based solid solution, CuAl2, Al6Mn and Al20Cu2Mn3 phases of solidification origin were identified after casting. The high temperature ageing of as-cast samples (T5 treatment) in a temperature range of 300–350 °C led to the formation of the metastable θ′ phase and equiaxed precipitates of the quasicrystalline-structured I-phase. The θ′ phase demonstrated a high size stability in a studied temperature range with a mean length of ~300 nm and a mean thickness of ~24 nm. A mean size of the I-phase precipitates varied in a range of ~30–50 nm depending on the treatment regimes. The rod-shaped T-phase precipitates were formed with an increase in ageing temperature to 400 °C. Mechanical properties were analyzed at room temperature in a solid solution-treated state. The increased yield strength at room temperature and 200–300 °C were observed after ageing at 300 °C for 148 h.

Microstructure Evolution, Constitutive Modelling, and Superplastic Forming of Experimental 6XXX-Type Alloys Processed with Different Thermomechanical Treatments.

This study focused on the microstructural analysis, superplasticity, modeling of superplastic deformation behavior, and superplastic forming tests of the Al-Mg-Si-Cu-based alloy modified with Fe, Ni, Sc, and Zr. The effect of the thermomechanical treatment with various proportions of hot/cold rolling degrees on the secondary particle distribution and deformation behavior was studied. The increase in hot rolling degree increased the homogeneity of the particle distribution in the aluminum-based solid solution that improved superplastic properties, providing an elongation of ~470-500% at increased strain rates of (0.5-1) × 10-2 s-1. A constitutive model based on Arrhenius and Beckofen equations was used to describe and predict the superplastic flow behavior of the alloy studied. Model complex-shaped parts were processed by superplastic forming at two strain rates. The proposed strain rate of 1 × 10-2 s-1 provided a low thickness variation and a high quality of the experimental parts. The residual cavitation after superplastic forming was also large at the low strain rate of 2 × 10-3 s-1 and significantly smaller at 1 × 10-2 s-1. Coarse Al9FeNi particles did not stimulate the cavitation process and were effective to provide the superplasticity of alloys studied at high strain rates, whereas cavities were predominately observed near coarse Mg2Si particles, which act as nucleation places for cavities during superplastic deformation and forming.

The influence of the main alloying elements on the formation of the initial grain structure, on phase transformations and on structural changes that occur during superplastic deformation of alloys Al - 4.1 wt.% Mg - 0.5 wt.% Zr, 1420T, 1421, 1423

The article presents the results of research aimed at revealing the influence of the main alloying elements on the formation of the initial grain structure, on phase transformations and on structural changes that occur during superplastic deformation of several aluminum alloys. It was possible to form a homogeneous ultrafine-grained structure in samples of alloys Al - 4.1 wt.% Mg - 0.5 wt.% Zr and 1423 due to dynamic recrystallization during their superplastic deformation. It is revealed that the initial microstructure of the 1420T alloy samples is bimodal. The average grain size is approximately 5 μm, in some areas of the working part of the samples there are large elongated grains, the average size of which is approximately equal to 25 μm. The initial structure of alloy 1421 samples is fine-grained, and the initial structure of alloy 1423 samples is multi-grained and coarse-grained. Metallographic studies showed that the grain structure of samples of alloys 1420T, 1421 and 1423 increases slightly during superplastic deformation at high homologous temperatures. Cavitation accumulates in the samples and structural changes occur, which are probably associated with local melting at grain boundaries and at interphase boundaries. It was established that the presence of zirconium and scandium additions in the composition of the samples ensures the formation of an ultrafine-grained structure in them and counteracts the grain growth during superplastic flow. Magnesium and lithium, which are included in the samples of the studied alloys 1420T, 1421 and 1423, form several intermetallic phases with aluminum. These phases are part of mixtures of crystals of peritectic origin, which are localized in the form of layers between some grains. The occurrence of peritectic reactions at high homologous temperatures can be one of the reasons for the partial melting of samples of alloys 1420T, 1421, and 1423 during their superplastic deformation. Partial melting of samples of alloys 1420T, 1421 and 1423 can probably be carried out due to the presence of segregations of magnesium and lithium at the grain boundaries, which lower the melting temperature of the aluminum-based solid solution. Partial melting of samples of alloys 1420T, 1421, and 1423 during their superplastic deformation, which is performed at high homologous temperatures, leads to the formation of cells of a metastable liquid-solid phase at the grain boundaries, the viscous flow of which leads to the formation of fibrous structures due to the development of grain boundary sliding.

The structural phase state and strength properties of the surface layer of AA6111-T4 aluminum alloy irradiated by the high-current electron beam

The effect of pulsed electron beam treatment on the structural phase state and strength properties of the AA6111-T4 aluminum alloy was studied. The irradiation led to the formation of a surface layer with a modified structural phase state. The results showed that an oversaturated aluminum-based solid solution is the main phase of the modified layer. Intermetallic phases which were found in the initial state of the alloy, weren’t detected in the modified layer using X-ray diffraction methods. The surface layer is characterized by the high-speed cellular crystallization structure with dimensions of 0.7 μm. The microhardness of the irradiated layer increased by more than 30%. Surface hardening parameters and mechanisms were clarified by investigation of the microstructural modification and the phase transformation both pre and post irradiation. It was shown that the grain boundary and solid solution hardening mechanisms play the key role in increasing the microhardness of the irradiated layer.

The influence of minor additions of Y, Sc, and Zr on the microstructural evolution, superplastic behavior, and mechanical properties of AA6013 alloy

Alloy AA6013 (Al-Mg-Si-based aluminum alloy) is of particular interest to the aerospace and automotive industries because of its attractive combinations of properties, however, accelerated grain growth at elevated temperatures limits its superplastic formability. The motivation for this study was to refine grain structure and control grain growth at elevated temperature in order to eliminate the lack of superplasticity in the alloy. For this reason, minor additions of Y, Sc, Zr were considered and their influence on the microstructural evolution, superplastic deformation behavior, and room temperature mechanical properties of a novel AA6013-type alloy was studied. A noticeable refinement of as-cast grain structure was observed due to the co-effect of Sc, Zr, Y additions. It was demonstrated that the Mg2Si phase and Y-bearing phases were formed during solidification of the studied alloys. The phases of silidification origin were fragmented during thermo-mechanical treatment led to the near uniform distribution of coarse particles of 0.5–0.8 µm size in the matrix. The coarse particles caused grain refinement during the superplastic deformation due to the particle stimulated nucleation (PSN) effect. In the alloy containing yttrium, during the decomposition of the aluminum-based solid solution supersaturated by Y, Zr, Sc, the following two precipitation mechanisms were involved: continuous precipitation resulting in the formation of nanoscale L12 phase dispersoids distributed homogeneously throughout the aluminum matrix and discontinuous precipitation that caused fan-shaped aggregations of the same phase near the high-angle grain boundaries. The nanoscale continuously-formed dispersoids retarded the recrystallization and dynamic grain growth during superplastic deformation due to Zenner pinning mechanism. Both PSN and Zenner pinning effects led to the grain refinement and achievement of superplasticity. The maximum elongation of 470% was observed under the test condition of T = 520 °C and ɛ.= 1 × 10−3 − 5 × 10−2 s −1. The room temperature tensile test revealed the following maximum characteristics of the sheet of the alloy with Y additions: yield strength of 330 MPa, ultimate tensile strength of 375 MPa, and elongation at fracture of 10%.

Evolution of strength properties and defect sub-structure of the hypoeutectic A319.0 alloy irradiated by a pulsed electron beam and fractured under tensile stress

The paper intends to investigate strength and plasticity properties and defect sub-structure of the hypoeutectic А319.0 alloy irradiated by a pulsed electron beam. The study has established and the revealed extinction contours point out that the irradiation of the А319.0 alloy by a pulsed electron beam brings about the formation of an up to 100 µm thick surface layer in the elastic-stressed state. The structure of the modified layer comprises nano-dimensional non-equiaxed cells. The reason for the non-equiaxity in a cellular structure is suggested to be the irregular heat removal from the surface of modification. X-ray microspectroscopy has found out that high-speed crystallization cells are formed by an aluminum-based solid solution and separated with thin layers, which are enriched mainly by silicon atoms and, to a smaller degree, by atoms of magnesium, iron and copper.The data obtained in the mechanical testing suggest that the irradiation was carried out in the following conditions: 50 J/cm2 and 50 µs results in the simultaneous enhancement of strength (by 22%) and plasticity (by 44%) properties of the А319.0 alloy – these are the best positive values in the set of conducted experiments. The study on А319.0 alloy samples irradiated and fractured under the tensile stress has highlighted that their fracture is dominated by the mechanism of intercrystalline quasi-brittle rupture caused by forming lengthy thin layers of the second phase along the boundaries of high-speed crystallization cells.

Structural Changes in the Surface of AK5M2 Alloy under the Influence of an Intense Pulsed Electron Beam

The surface of AK5M2 (Al–Si) alloy is treated with an intense pulsed electron beam in various modes (accelerated electron energy of 17 keV, electron-beam energy density of 10, 20, 30, 40 and 50 J/cm2, pulse duration of 50 and 200 μs, the number of pulses 3, and the pulse repetition rate 0.3 s–1). Microhardness analysis is performed, and the elemental and phase composition and state of the defect substructure of the surface layer are studied by scanning electron microscopy and X-ray phase analysis. It is shown that the increase in microhardness of the Al-Si alloy is due to the formation of a submicrometer-sized structure of high-speed cellular crystallization, the enrichment of an aluminum-based solid solution with alloying and impurity elements, and the reprecipitation of nanoscale particles of strengthening phases. It is suggested that the higher values of the microhardness found in the alloy irradiated at 50 J/cm2 and 50 μs compared with the alloy irradiated at 50 J/cm2 and 200 μs are due to the process of tempering the material, which have a greater development with a longer duration of exposure to beam electrons per pulse.

Evaluation of Microstructure and Hardness of Novel Al-Fe-Ni Alloys with High Thermal Stability for Laser Additive Manufacturing

The microstructure and phase composition of cast and laser-melted Al-Fe-Ni alloys were investigated. Two main phases—Al3(Ni,Fe) and Al9FeNi—were formed in the as-cast state. A fine microstructure without porosity or solidification cracks was observed in the Al-Fe-Ni alloys after laser treatment. The hardness of the laser-melted alloys was 2.5–3 times higher than the hardness of the as-cast alloys owing to the formation of an aluminum-based solid solution and fine eutectic particles. The formation of the primary Al9FeNi phase was suppressed as a result of the high cooling rate. Annealing these alloys at temperatures less than 300°C demonstrated the high thermal stability of the microstructure while maintaining the hardness. The Al-Fe-Ni alloys investigated in this study are promising heat-resistant materials for additive manufacturing because of their fine, stable structure, and the low interdiffusion coefficients of Fe and Ni.

Structure Formation in the Melt-Quenched Al–12.2Si–0.2Fe Alloys

The microstructure, the phase composition, the component distribution, and the grain structure of the commercial eutectic Al–12.2 Si–0.2 Fe (at %) silumins formed at cooling rates of 102 and 105 K/s are studied. Three phases are detected in the alloy after solidification at both cooling rates: α-aluminum, silicon, and an iron-containing phase. The bulk samples have a heterogeneous dendritic structure with large dendrites of an aluminum-based solid solution, and a eutectic lamellar mixture of aluminum and silicon filling the interdendritic space. The melt-quenched foils are characterized by a homogeneous microstructure over the thickness; however, they have a layered structure. The rapidly solidified foils also have a homogeneous granular structure through the thickness and no pronounced texture. The mechanisms of solidification and microstructure formation are proposed for both the bulk samples and the melt-quenched foils.

Effect of cold plastic deformation and subsequent aging on the strength properties of Al-Mg2Si alloys with combined (Sc + Zr) and (Sc + Hf) additions

Effects of equal-channel angular pressing (ECAP) and rotary swaging (RS) with subsequent aging on the strength properties of Al-Mg2Si alloys with (Sc + Zr) and (Sc + Hf) additions were studied. The microstructure of deformed alloys was examined by optical and transmission electron microscopy (TEM). Mechanical properties were characterized by hardness measurements and tensile testing. It was found that the strength properties of Al-Mg2Si alloys were remarkably improved due to the structure refinement during cold deformation and the acceleration of the kinetics precipitation of the βʹ and βʹʹ phases during aging of deformed alloys. It is found an accelerated decomposition of the supersaturated aluminum-based solid solution in the presence of hafnium. Nearly the same values of hardness and tensile strength of Al-Mg2Si alloys with transition metals additions have been accounted for the more intense decomposition of the solid solution with hafnium has compensated by a larger amount of hardening phases (βʹʹ and βʹ) in alloys with zirconium. For all alloys the highest hardness was achieved after cold deformation and remained nearly the same after 2 h of aging.

Rapid quenching effect on the microstructure of Al-Si eutectic Zn-doped alloy

The authors present results of a study on microstructure, phase composition, component distribution of alloy Al – 12.2 at.% Si – 0.2 at.% Fe doped by Zn, obtained at cooling rates of 102 and 105 K/s. At both cooling rates the alloys are characterized by the presence of three phases: aluminum-based solid solution, silicon, and iron-containing phase. Bulk samples are characterized by a heterogeneous structure: large dendrites of a solid solution based on aluminum, and a eutectic lamellar mixture of aluminum and silicon localized in interdendritic space. The rapidly solidified foils differ by a uniform composition in thickness, the microstructure is however layered. The mechanisms of solidification and the formation of a microstructure are proposed for both bulk samples and rapidly solidified foils.

Microstructure and mechanical properties of doped and electron-beam treated surface of hypereutectic Al-11.1%Si alloy

The effect of electroexplosive doping in two modes with subsequent intense pulsed electron beam treatment of hypereutectic Al-11.1%Si alloy (silumin) on the change of its structure and phase composition, mechanical and tribological properties has been investigated. Methods of methods of scanning electron microscopy, electron microprobe and X-ray diffraction analysis were used to analyze changes of the structure, phase composition, and morphology of the modified surface of hypoeutectic silumin subjected to a complex treatment. Change of tribological and mechanical properties after the complex energy deposition is evaluated: the microhardness increases by 3.2 times (2.34GPa in contrast to 0.73GPa in the as-cast state), the wear parameter (inverse to the wear resistance) decreases by 18–20 times (from 49⋅10−4mm3/N⋅m to 2.5⋅10−4mm3/N⋅m) and the friction coefficient decreases by ≈1.5 times (from 0.55 to 0.36). It is revealed that a complex treatment mode hardly affects the studied properties but it has a strong effect on the phase composition of a modified layer (the content of the aluminum-based solid solution is reduced by 2.5 times, and the relative content of silicon oxide grows by ≈2.2 times). The multiphase submicro- and nanocrystalline structure formed in the surface layer is responsible for changes in the wear resistance and microhardness, and special features of the thermal action by an intense pulsed electron beam on the surface govern a decrease in the friction coefficient.

Phase composition of hypereutectic silumin at rapid solidification

The paper presents the results of the study of the phase composition of hypereutectic silumin Al – 16.0 at. % Si – 0.2 at. % Fe. A comparative analysis of the phase composition of samples obtained at an average melt cooling rate of 102 K/s and at an ultra-high melt cooling rate of 105 K /s was carried out. At an average rate, the samples solidified in a graphite mold, and the ultra-high melt cooling rate was provided during the production of foils by the method of ultrafast quenching from the melt. It was established by X-ray diffraction and micro X-ray spectral analysis that the rapidly solidified foils consist of an aluminum-based solid solution supersaturated by silicon, dispersed silicon particles and the AlFeSi2 ternary compound phase. Comparative analysis of the results of X-ray diffraction and X-ray spectral studies of samples obtained at different melt cooling rates indicate that, during rapid solidification, the aluminum-based supersaturated solid solution contains up to 2 at. % Si.

Investigation into the Structure and Properties of Solders Based on Aluminum and Zinc in the Form of Cast Rods of a Small Cross Section

Solders of the Al–Cu–Si system (A34 brand) and Zn–Al–Cu system (Welco52 brand) are investigated. It is found that the A34 solder (Al–28% Cu–6% Si) melts and crystallizes in a narrow temperature range (~18°C). Solidus and liquidus temperatures of the A34 solder are ~508 and ~526°С, respectively. Solders of the Zn–Al–Cu system (Zn–4% Al–2.5% Cu) have an eutectic composition that provides melting and crystallization at a constant temperature of ~389°С. Densities of studied solders in liquid and solid states are investigated. Their values for the solder of the A34 brand are 3.02 and 3.32 g/cm3, respectively, and, for the zinc solder, 6.28 and 6.69 g/cm3. The influence of casting conditions on the structure of cast alloys in the form of rods with a cross-section area of 13, 10, and 5 mm2 is investigated. The main structural components of solder alloys refine with a decrease in the cross-section area. Dendrites of the aluminum-based solid solution and CuAl2 phase refine in the microstructure of the A34 solder. Dendrite sizes of the zinc-based solid solution most noticeably decrease in the zinc solder. The largest castability is characteristic of alloys fabricated from rod solders with a cross section of 5 mm2 for studied gaps in the sampling of 2.0, 1.5, and 1.0 mm. The zinc solder of the eutectic composition has the best castability when compared with the A34 solder: this characteristic for the melt formed from the zinc-based solder rod with a cross section of 5 mm2 and a gap width in the sampling of 2.0 mm is 100% (the melt of the A34 solder formed from the rod of the same cross section has a castability of 98%). The results of experiments on soldering plates made of the AK12 alloy and sheets made of the AMts alloy show the presence of a tight boundary in the “solder–base material” system, as well as the absence of discontinuities in the form of pores and unsoldered regions. An insignificant interpenetration of solder alloys into the base material is observed, especially when soldering cast plates made of the AK12 alloy.

Effect of scandium on the phase composition and hardening of casting aluminum alloys of the Al–Ca–Si system

The phase composition of the Al–Ca–Si–Sc system is investigated in aluminum corner uisng computational (Thermo-Calc) and experimental (optical microscopy, scanning electron microscopy, and electron probe microanalysis) methods. The influence of annealing on the structure and hardness of alloys containing 0.3 wt % Sc is investigated in the region up to 550°C. It is shown that the maximum in the hardening curve caused by the isolation of nanoparticles of the Al3Sc (L12) is attained after annealing at temperatures of 300–350°C in alloys belonging to the phase region (Al) + Al4Ca + Al2Si2Ca ((Al) is the aluminum-based solid solution). Scandium completely enters the (Al) composition in alloys of this region, while the silicon concentration is minimal in it. On the other hand, hardening is almost absent in alloys from the (Al) + (Si) + Al2Si2Ca phase region. The possibility in principle to form the casting alloys based on the (Al) + Al4Ca + Al2Si2Ca eutectic hardened without quenching is substantiated.

High-pressure phase transitions and structure of Al–20 at % Si hypereutectic alloy

Phase transformations of an Al–20 at % Si high-silicon hypereutectic alloy have been studied by differential barothermal analysis at temperatures of up to 800°C in argon compressed to 100 MPa. High pressure has been shown to raise the melting point of the alloy by 5°C during heating and to lower the eutectic solidification temperature by 5°C during cooling in comparison with the canonical phase diagram of the Al–Si system. At a temperature of 553°C, heating and cooling lead to silicon dissolution and decomposition of the aluminum-based solid solution, respectively. After high-pressure solidification, the silicon particles in the alloy have a bimodal size distribution. Quantitative porosity characteristics in the alloy after a barothermal scanning cycle are similar to those in the as-prepared alloy. The lattice parameters of the silicon and aluminum remain unchanged. The microhardness of the aluminum matrix of the alloy corresponds to that of pure aluminum.

Effect of lead on the structure and phase composition of an Al–5% Si–4% Cu casting alloy

The phase transformations in the Al–Cu–Si–Pb system have been studied using calculations. It is shown that the aluminum-based solid solution is in equilibrium only with the Al2Cu, (Si), and (Pb) phases, which correspond to the relevant binary systems. Reported polythermal and isothermal sections show that the Al–Cu–Si–Pb system is characterized by a significant liquid miscibility gap. The effect of lead on the structure and phase composition of an Al–5% Si–4% Cu alloy in the as-cast and annealed states is studied. Lead inclusions are located at the boundaries of dendritic (Al) cells and are globular in the as-cast alloy and after annealing at 500°C. The presence of lead phase does not affect the precipitation hardening upon quenching and aging.

Barothermography and microstructure of the hypoeutectic and eutectic alloys in Al–Si system

Differential barothermal analysis (DBA or HP-DTA) of the phase transformations in hypoeutectic Al-10 at.% Si and eutectic Al-12 at.% Si alloys was carried out at 100 MPa of argon pressure and at temperatures up to 700 °C. Liquidus temperature of Al-10 at.% Si is reduced during melting and crystallization by 3–4 °C as compared with the atmospheric pressure data. Increase in the eutectic transformation L → (Al) + Si temperature up to 580–581 °C during heating was found for the Al-10 at.% Si and Al-12 at.% Si alloys. According to the barothermography data, a slight thermal effect at 553 °C is detected for both alloys, which was identified as the decomposition of aluminum-based solid solution and precipitation of silicon particles. The improvement of silicon phase morphology for Al-10 at.% Si and Al-12 at.% Si alloys after hot isostatic pressing (HIP) at the pressure of 100 MPa and temperature of 550 °C was found. No porosity in the alloy has been established after HIP treatment. After HIP thermal expansion, coefficients of the alloy are noticeably decreased by 25 (Al-10 at.% Si) and 50 % (Al-12 at.% Si).

Structural and phase transformations in aluminum-copper alloys under the effect of electroplastic deformation

The deformational structure and the phase composition of binary and commercial aluminumcopper alloys produced using electroplastic deformation by rolling (EPDR) have been studied. It has been shown that structural transformation in the materials and changes in their hardness in the course of EPDR are governed by the initial state, which determines the distribution and the thermomechanical stability of a dislocation ensemble. It has been found that EPDR causes the dynamic deformation-induced aging of the aluminum-based supersaturated solid solution, which is accompanied by the precipitation of the strengthening θ phase in the Al-Cu alloy and the S phase in the D16 alloy.