Temperature Dependence of the Dynamics of Portevin-Le Chatelier Effect in Al-2.5 Pct Mg Alloy

Tensile tests were carried out by deforming polycrystalline samples of Al-2.5 pct Mg alloy at four different temperatures in an intermediate strain rate regime of 2 × 10⁻⁴ s⁻¹ to 2 × 10⁻³ s⁻¹. The Portevin-Le Chatelier (PLC) effect was observed throughout the strain rate and temperature region. The mean cumulative stress drop magnitude and the mean reloading time exhibit an increasing trend with temperature, which is attributed to the enhanced solute diffusion at higher temperature. The observed stress–time series data were analyzed using the nonlinear dynamical methods. From the analyses, we established the presence of deterministic chaos in the PLC effect throughout the temperature regime. The dynamics goes to higher dimension at a sufficiently high temperature of 425 K (152 °C), but the complexity of the dynamics is not affected by the temperature.     

Microstructural Evolution of the Interdiffusion Zone between U-9 Wt Pct Mo Fuel Alloy and Zr-1 Wt Pct Nb Cladding Alloy Upon Annealing

Diffusion couple formed between U-9 wt pct Mo and Zr-1 wt pct Nb alloys, proposed as fuel and clad materials, respectively, in nuclear research reactors, was annealed to investigate the microstructural evolution of the interdiffusion zone (IZ) as a function of temperature. A layered-type IZ microstructure was observed, the mechanism of development of which was elucidated. Mo₂Zr phase, present as dispersoids, in the U-rich part of the as-bonded IZ evolved into a continuous layer and into a “massive” morphology upon annealing. The discontinuous precipitation reaction in the matrix adjoining the Mo₂Zr phase, instigated by Mo depletion, generated lamellae of α-U phase within the γ-U(Mo,Zr) matrix. Zr-rich α-Zr(U) precipitates were observed in U-rich U-Mo-Zr matrix in the IZ next to the U-9Mo base material due to the clustering tendency of the matrix phase. The IZ next to Zr-1Nb base material comprised a “basket weave” microstructure of α-Zr laths with β-Zr(Nb,U) interlath boundaries, wherein an omega like transformation of the latter to δ-UZr₂ was also noticed. The growth rates of the IZ were orders of magnitude lower when compared with the ones reported between the compositionally similar U-10 wt pct Mo alloy and the presently used Al or Al-Si cladding alloys.     

Effect of Manganese on the Formation of Fe-rich Phases in Electromagnetic Stirred Hypereutectic Al-22Si Alloy with 2 % Fe

The effect of Mn on the microstructure of electromagnetic stirred hypereutectic Al-22Si-2Fe (% w/w) alloys was studied. The results show that the alloy with a Mn/Fe ratio zero, contained plentiful α-Al₄FeSi₂ phases existing as mainly intermetallic compounds in the solidified microstructures by electromagnetic stirring (EMS) process. With EMS process, the alloy with 0.61 % Mn contained acicular β-Al₅(Fe, Mn)Si, δ-Al₄(Fe, Mn)Si₂ and blocky α-Al₁₅(Fe, Mn)₃Si₂ phases in the solidification microstructure of the stirred A1 alloy. As the Mn/Fe ratio increased to 1, intermetallic compounds were mainly in the form of blocky and fine α-Al₁₅(Fe, Mn)₃Si₂ phases in the microstructure. The intermetallic compounds were examined with an optical microscope, scanning electron microscope, and X-ray diffraction. The acicular δ-Al₄(Fe, Mn)Si₂ and blocky α-Al₁₅(Fe, Mn)₃Si₂ phases were also analyzed by transmission electron microscopy.     

Effect of Repair Welding on Electrochemical Corrosion and Stress Corrosion Cracking Behavior of TIG Welded AA2219 Aluminum Alloy in 3.5 Wt Pct NaCl Solution

The stress corrosion cracking (SCC) behavior of AA2219 aluminum alloy in the as-welded (AW) and repair-welded (RW) conditions was examined and compared with that of the base metal (BM) in 3.5 wt pct NaCl solution using the slow strain rate technique (SSRT). The reduction in ductility was used as a parameter to evaluate the SCC susceptibility of both BM and welded joints. The results show that the ductility ratio (ε _NaCl/(ε _air)) of the BM was close to one (0.97) and reduced to 0.9 for the AW joint. This value further reduced to 0.77 after carrying out one repair welding operation. However, the RW specimen exhibited higher ductility than the single-weld specimens even in 3.5 wt pct NaCl solution. SSRT results obtained using pre-exposed samples followed by post-test metallographic observations clearly showed localized pitting corrosion along the partially melted zone (PMZ), signifying that the reduction in ductility ratio of both the AW and RW joints was more due to mechanical overload failure, caused by the localized corrosion and a consequent reduction in specimen thickness, than due to SCC. Also, the RW joint exhibited higher ductility than the AW joint both in air and the environment, although SCC index (SI) for the former is lower than that of the latter. Fractographic examination of the failed samples, in general, revealed a typical ductile cracking morphology for all the base and welded joints, indicating the good environmental cracking resistance of this alloy. Microstructural examination and polarization tests further demonstrate grain boundary melting along the PMZ, and that provided the necessary electrochemical condition for the preferential cracking on that zone of the weldment.     

Effect of Temperature on Microstructure and Formability of Al-10 mass％ Si Coatings

The type-1aluminized(Al-10mass% Si)coating on hot stamped steel is used in commercial applications.The effect of temperature on microstructure and formability of the Al-10mass% Si coating was investigated.Hot-dip aluminized 22MnB5 steel was heated at 870,900,930,and 1 050 ℃ for 5 min.After heat treatment at different temperatures,the microstructure of Al-10mass% Si was characterized by field-emission scanning electron microscopy and energy-dispersive spectroscopy.The results show that when the Al-10mass% Si coating was heated at 870℃for 5min,three types of intermetallic phases were formed:two ternary Fe-Si-Al phases(Fe2SiAl7+Fe2Si2Al5and Fe2SiAl2+Fe2Si2Al5)and one binary Fe-Al phase(FeAl3).The phases in the coating became Fe2SiAl2+Fe2Si2Al5and FeAl3,the binary Fe-Al phase near the interface became Fe2Al5 and the Si-rich layers were decreased with the increase of heating temperature.When the heat treatment was 1 050℃for 5min,the Si-rich layer disappeared,the coating consisted of FeAl and Fe3 Al,and the Kirkendall voids were formed.When the heating temperature was increased through 870,900,and 930℃,the coating hardness was reduced and cracks were formed in the coating after hot stamping.The formability of the coating with temperature change was confirmed by a hot stamping test.When heated at 1 050 ℃,the coating was formable but continuous Kirkendall voids were observed.     

Effects of Route on Microstructural Evolution and Mechanical Properties of Cu-8 Wt Pct Ag Alloy Processed by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) is applied to investigate the microstructural evolution and mechanical properties of Cu-8 wt pct Ag alloy subjected to one to four passes via four different routes (A, B_A, B_C, and C). It is demonstrated that better mechanical properties, a higher fraction of high-angle boundaries, and a smaller grain size can be obtained most rapidly with route A, whereas the specimen processed by route B_C contains relatively inhomogeneous microstructure and has poor mechanical properties. The ultimate tensile stress (UTS) of the Cu-Ag alloy processed by route B_C saturates after four passes; in contrast, the UTS of the Cu-Ag alloy processed by route A increases continuously in relation to the number of ECAP passes. Based on the experimental results, the strengthening mechanisms of the Cu-8 wt pct Ag alloy processed by different routes as well as the efficiency of different routes in refining the binary alloy are discussed.     

The Effect of Small Additions of Fe and Heavy Deformation on the Precipitation in an Al–1.1Mg–0.5Cu–0.3Si At. Pct Alloy

Metallurgical and Materials Transactions A - The effect of 0.03 and 0.08 at. pct Fe additions on the formation of secondary phases in an Al–1.1Mg–0.5Cu–0.3Si at. pct alloy was...     

Electrolytic Deposition and Diffusion of Lithium onto Magnesium-9 Wt Pct Yttrium Bulk Alloy in Low-Temperature Molten Salt of Lithium Chloride and Potassium Chloride

The electrolytic deposition and diffusion of lithium onto bulk magnesium-9 wt pct yttrium alloy cathode in molten salt of 47 wt pct lithium chloride and 53 wt pct potassium chloride at 693 K were investigated. Results show that magnesium-yttrium-lithium ternary alloys are formed on the surface of the cathodes, and a penetration depth of 642 μm is acquired after 2 hours of electrolysis at the cathodic current density of 0.06 A·cm⁻². The diffusion of lithium results in a great amount of precipitates in the lithium containing layer. These precipitates are the compound of Mg₄₁Y₅, which arrange along the grain boundaries and hinder the diffusion of lithium, and solid solution of yttrium in magnesium. The grain boundaries and the twins of the magnesium-9 wt pct yttrium substrate also have negative effects on the diffusion of lithium.     

Electropulsing Induced Texture Evolution in the Recrystallization of Fe-3 Pct Si Alloy Strip

Electropulsing induced texture evolution in the primary recrystallization of a Fe-3 pct Si alloy strip was studied using the electron backscattered diffraction technique. The results revealed that the electropulsing strengthened considerably the recrystallization of a cold-rolled Fe-3Si alloy strip. Various textures with high-energy storages, such as α (100)〈110〉, γ (111)〈110〉, γ (111)〈112〉, and G-texture (110)〈001〉, formed after several seconds of electropulsing treatment (EPT), depending on the intensity of electropulsing. The athermal effect of electropulsing is 319 times stronger than the thermal effect of electropulsing for the formation of the G texture. The mechanism of electopulsing induced texture evolution is discussed from the point of view of Gibbs free energy and dislocation dynamics.     

Effect of the Intercritical Annealing Temperature on the Mechanical Properties of 10 Pct Mn Multi-phase Steel

Intercritically annealed 10 pct Mn steel has been shown to exhibit an excellent combination of strength and ductility due to the plasticity-enhancing mechanisms of mechanical twinning and strain-induced martensite transformation occurring in sequence. This mechanical behavior is only achieved for a multi-phase microstructure obtained after annealing within a specific intercritical temperature range. A model for the selection of the optimal intercritical annealing temperature was developed to achieve a high strength-ductility balance for 10 pct Mn multi-phase steel. The model considers the room temperature stacking fault energy and the thermodynamic stability of the retained austenite.     

Combined Effect of Calcium and Silicon on the Phase Composition and Structure of Al–10%Mg Alloy

Phase transformations in the Al–Ca–Mg–Si system in the region of aluminum–magnesium alloys are investigated using the Thermo-Calc program. The liquidus projection of the quaternary system is constructed with a Mg content of 10% and it is shown that phases Al4Ca, Mg₂Si, and Al₂CaSi₂ can crystallize (in addition to the aluminum solid solution (Al)) depending on the calcium and silicon concentrations. The crystallization character of quaternary alloys is investigated with the help of a polythermal cross section calculated at concentrations of 10% Mg and 84% Al. Based on the analysis of phase transformations occurring in alloys of this section, the presence of the Al–Al₂CaSi₂–Mg₂Si quasi-ternary section in the Al–Ca–Mg–Si system was assumed. Three experimental alloys were considered from a quantitative analysis of the phase composition, notably, Al–10% Ca–10% Mg–2% Si, Al–4% Ca–10% Mg–2% Si, and Al–3% Ca–10% Mg–1% Si. Metallographic investigations and electron-probe microanalysis were performed using a TESCAN Vega 3 scanning electron microscope. Critical temperatures are determined using a DSC Setaram Setsys Evolution differential calorimeter. The experimental results agree well with the calculated data; in particular, a peak at t ~ 450°C is revealed for all alloys in curves of the nonequilibrium solidus and invariant eutectic reaction L → (Al) + Al₄Ca + Mg₂Si + Al₃Mg₂. It is established that the structure of the Al–3% Ca–10% Mg–1% Si alloy is closest to the eutectic alloy. It is no worse that the AMg10 alloy in regards to density and corrosion resistance and even surpasses it in hardness, which allows us to consider this alloy as the basis for the development of a new cast material: “natural composites.”     

Effect of Yttrium Addition on Microstructures and Room Temperature Tensile Properties of Ti-47Al Alloy

The microstructures and room temperature tensile properties of a series of Ti-47Al-xY （x = 0%, 0.1%, 0.3%, 0.5%, 0.7% and 1.0%（atom fraction）） were investigated systemically. Results show that both the grain size and lamellar spacing decrease remarkably with the increase of Y content. When the content of Y is greater than 0.1%, most of the Y elements accumulate along the grain boundaries and some fine particles are uniformly dispersed within the grains in the form of YAl2 compound because of the low solubility and segregation of Y in TiAl alloys. Grain-boundary seg- regation of Y element is more prominent with the increase of Y addition. Good tensile properties are obtained when Y addition ranges from 0.3 % to 0.5 %. The refinement of grain and lamellar structures and dispersion of YAl2 within the grains contribute to the improvement of tensile properties. On the other hand, for high Y-added alloys （over 0.5% Y）, tensile properties are obviously deteriorated due to brittle cleavage fracture of the coarse YAl2 network.