Superplastic Conditions Research Articles

Effect of Sc/Zr ratio on superplastic behavior of ultrafine-grained Al–6%Mg alloys

Al–6%Mg-Sc-Zr alloys with a combined Sc and Zr ratio of 0.32 wt% make up the focus of this research. The content of Sc and Zr varied with an increment of 0.02%. Their ultrafine-grained (UFG) microstructure was formed with Equal Channel Angular Pressing (ECAP). Superplasticity tests were performed at temperatures ranging from 300 to 500 °C and at a strain rate varying between 3.3·10−3 and 3.3·10−1 s−1. The values of strain hardening factor (n), strain rate sensitivity factor (m), and superplastic deformation threshold stress (σp) were determined. The microstructure and failure patterns of the alloys post superplasticity tests were studied. The effect of the Sc/Zr ratio on the superplastic behavior, cavitation fracture and dynamic grain growth of UFG Al–6%Mg alloys was investigated. The satisfiability of Hart's criterion for calculating uniform deformation value under superplastic conditions was verified. Grain boundary sliding and intragranular deformation make comparable contributions to superplastic flow in the UFG aluminum alloys under study. Al–6%Mg-0.20%Sc-0.12%Zr (Sc/Zr = 3.3 at.%) and Al–6%Mg-0.18%Sc-0.14%Zr (Sc/Zr = 2.8 at.%) alloys exhibit the highest superplasticity. Shown that changes in the Sc/Zr ratio affect the precipitating mechanism, spatial distribution and composition of the precipitating particles Al3(ScxZr1-x). The optimal Sc/Zr ∼2.6–3.3 (at.%) ratio for the Al–6%Mg alloy corresponds to an Al3(Sc0.5Zr0.5) and Al3Sc precipitated particles. The large Al3Zr particles formed through the discontinuous precipitation mechanism was detected at Sc/Zr < 1 (at.%).

Preparation of a Solid-Phase Compound from an Aluminum–Zinc Alloy under Conditions of Low-Temperature Superplasticity

Preparation of a Solid-Phase Compound from an Aluminum–Zinc Alloy under Conditions of Low-Temperature Superplasticity

Microstructural evolution during superplastic deformation of commercial Al5083 alloy

The aluminum alloy SPF process has found extensive application in the aviation and rail transportation industries. The commercial Al5083 alloy presents the advantages of low density, high specific strength, a simplified manufacturing technique, and low cost, thus making it an appealing option for producing components with minor strain and complex configurations. This study focused on examining the mechanical properties of the commercially available Al5083 alloy. Different temperatures (450 °C, 480 °C, 510 °C) and strain rates (0.01 s−1, 0.005 s−1, 0.001 s−1, 0.0005 s−1) were employed to investigate the behavior of the material. Furthermore, a constitutive equation was developed to describe the alloy's response under superplastic conditions. The utilization of EBSD allowed for the investigation of the evolution of grain and dislocation density, while XRD was employed to determine the development of macroscopic texture strength and texture type. The dominant mechanism of superplastic deformation in the commercial Al5083 alloy was identified as dynamic recrystallization and intra-crystalline slip, which distinguishes it from conventional fine-grained aluminum alloys. SEM was used to establish the exponential relationship between void volume fraction and true strain. The results provide valuable insights into the evolution of the macro-mechanical properties and microstructure of commercial Al5083 alloy during superplastic forming.

Al-Mg-Mn-Zn-Zr alloy with refined grain structure to develop Al-B fiber-reinforced metal matrix composites compacted in superplastic conditions

Homogeneous nanostructured and ultrafine-grained states in an Al-Mg-Mn-Zn-Zr alloy were produced by high pressure torsion at room temperature and by continuous equal channel angular pressing at 200 °C. The alloys with refined grain structure in both states exhibited low temperature and high strain rate superplastic behavior. The nanostructured alloy with enhanced mechanical behavior was used for MMC fabrication under superplastic conditions guided with the help of finite element simulations. Computer-aided “foil-fiber-foil” process using a woven-alike boron fiber network and nanostructured Al alloy provided smooth defect-free compaction of an Al-B fiber-reinforced composite under superplastic conditions at a temperature of 300 °C.

Overview: Using Severe Plastic Deformation in the Processing of Superplastic Materials

In tensile testing, polycrystalline materials generally fail at relatively low total elongations but under some limited conditions it is possible to achieve exceptionally high elongations of up to and exceeding 400%. This superplastic condition is important scientifically but also it has important uses through the industrial development of superplastic forming operations. This overview traces the historical development of this superplastic effect and it provides a summary of the main characteristics of the superplastic flow process. Conventional thermomechanical processing is not able to produce exceptionally small grain sizes within the submicrometer or nanometer range but this limitation was effectively overcome through processing using severe plastic deformation (SPD). The advantages of SPD processing are discussed and examples are presented. Finally it is demonstrated that the experimental data may be easily and effectively displayed through the construction of deformation mechanism maps based on combinations of stress, grain size and temperature.

Welding the Solid State of Zn–22% Al Alloy under Low-Temperature Superplasticity Conditions

Welding the Solid State of Zn–22% Al Alloy under Low-Temperature Superplasticity Conditions

Technological properties of sheet titanium alloys VT6

This paper presents a comprehensive study of the microstructure, mechanical and technological properties (formability and weldability in solid state) of sheet blanks made of titanium alloy VT6, developed specifically for superplastic forming and diffusion bonding (SPF / DB) in PJSC VSMPO-AVISMA Corporation using various technologies. The conducted studies have made it possible to establish that sheets of titanium alloy VT6 with different microstructure in the temperature range of 850 – 920°C exhibit good superplastic properties. Studies of the technological properties of experimental sheets show their good weldability and high formability under superplasticity conditions. The relative length of the pores in the zone of the solid-phase joints is from 5.3 to 1.8 %, the equivalent deformation during SPF is from 1500 to 2700 %. The technological properties of the VT6 alloy in different states are very similar. The results obtained allow us to recommend this experimental sheet alloy for the manufacture of hollow structures by the SPF / DB process under superplasticity.

Obtaining of a solid-phase compound from an aluminum-zinc alloy under conditions of low-temperature superplasticity

A method is developed for pressure welding of cylindrical workpieces in the solid state of an aluminum-zinc alloy in a vacuum at a temperature of 250 °C under conditions of low-temperature superplasticity. Tensile tests showed that the strength of the welded joints is 90÷95 % of the tensile strength of the base material. Keywords ultrafine-grained structure, aluminum-zinc alloy, low-temperature superplasticity, solid-phase compound, welding using pressure, mechanical properties

Distribution of the temperature in friction stir welding of aluminum and copper alloys

Friction stir welded are studied joints of pure copper M1 and aluminum alloy AD1. A technique for measuring the temperature was developed at the points of the weld. The results of measurement temperature are given in friction stir welding at various speeds of rotation of the welding tool (800-1000 rpm), welding speed (25-61 mm/min). The temperature reached in copper is about 60 K higher than in aluminum. The higher cooling rate of copper is due to the greater thermal diffusivity than that of aluminum. The maximum temperature in the copper reached 769 K, which was lower than the melting point of the eutectic in the Al-Cu system (821 K). The residence time above the temperature of formation of intermetallic compounds (623 K) is much shorter than the duration of the thermal cycle (50 s). With an increase in the welding tool rotation frequency from 800 to 1000 rpm, the maximum temperature near the pin increases from 650 to 769 K. At a tool rotation frequency of 800 rpm, the maximum temperature in copper achieved in the cycle is lower than the transition temperature to the superplastic state and is 764 K high heating and free cooling rates (50–145 K/s and 25–50 K/s) of the weld on the side of the copper alloy predetermine the short-term (from 5 to 15 s) stay of the metal in the temperature range of formation of intermetallic phases.

Superplastic forming of EK61 nickel-based superalloy with ultrafine-grained structure

The formation of an ultrafine-grained structure in the heat-resistant nickel-based EK61 superalloy makes it possible to realize the effect of low-temperature superplasticity. This is important for the development of resource-saving technologies for forming hollow products of complex configuration. The study of mechanical properties of the nickel-based EK61 superalloy with ultrafine-grained structure under conditions of uniaxial tension and compression at temperatures of 650 – 850°C and strain rates of 10−3 – 10−4 s−1 was carried out. The process of superplastic forming (SPF) under conditions of low-temperature superplasticity of ultrafine-grained sheet blanks from the EK61 superalloy using cylindrical matrix has been studied. It was found that after SPF, a homogeneous equiaxed ultrafine-grained duplex structure is preserved in the samples.

Permanent Joint Stability of Heat-Resistant Deformable Nickel and Cast Intermetallic Alloys Obtained under Superplasticity Conditions (Part II)

Permanent Joint Stability of Heat-Resistant Deformable Nickel and Cast Intermetallic Alloys Obtained under Superplasticity Conditions (Part II)

Permanent Joint Stability of Heat-Resistant Deformable Nickel and Cast Intermetallic Alloys Obtained under Superplasticity Conditions: Part 1

Permanent Joint Stability of Heat-Resistant Deformable Nickel and Cast Intermetallic Alloys Obtained under Superplasticity Conditions: Part 1

Surface studies of superplasticity in Al–Zn–Mg–Cu alloy via in-situ tensile test

The grain boundary sliding and its accommodation mechanism during superplastic deformation have been identified by surface observations with focused ion beam in an Al–Zn–Mg–Cu alloy. The high-temperature in-situ tensile test is carried out in the scanning electron microscope under the region Ⅱ superplastic conditions. The experiment results indicate that the grain boundary sliding is the dominant superplastic deformation mechanism accommodated by diffusion creep and a little dislocation activity. The grain rotation also plays an essential role in superplastic deformation. There are no striated zones found in a vacuum environment, just cracks. A grain boundary sliding model is proposed based on the surface features.

Influence of Friction Stir Welding Modes of Copper and Aluminum Alloys

The article discusses the influence of the parameters of friction stir welding modes on the formation of the outer surface of the weld and the thickness of the intermetallic layer for the thickness of the welded samples of 3 mm. Changing the rotation speed from 600 rpm to 1000 rpm of the welding tool allows you to control the amount of energy input to transfer the welded material into a superplastic state. The welding speed was varied from 20 mm/min to 80 mm/min. The most optimal mode was for an aluminum and copper alloy with a thickness of 3 mm, a rotation speed of 900 rpm, a welding speed of 25 mm/min, an angle of inclination of 30 at which the mechanical properties of the welded seam approached the most plastic material (aluminum). The article considered thermal cycles measured near the pin from the side of the aluminum and copper alloy. The maximum temperature was 900 K on a copper alloy. The parameters of welding modes also affect the formation of intermetallic layers. If the thickness of the intermetallic layer does not exceed 4-5 μm, then increased values of the mechanical strength of the welded dissimilar joint are observed.

Стабильность неразъемного соединения из жаропрочных деформируемого никелевого и литейного интерметаллидного сплавов, полученного сваркой давлением в условиях сверхпластичности (Часть II)

The article presents a study of welded joints of cast intermetallic single-crystal rhenium containing VKNA-25 alloy with crystallographic orientation [001] and deformable high-temperature disk nickel alloy EP975, depending on the parameters of pressure welding under superplasticity conditions and standart heat treatment for high-temperature disk nickel alloy with regulated single-phase cooling. The study was carries out for the interdendritic region. The results of X-ray micro-spectral analysis of a solid-phase joint in the welding zone and at distances of up to 140 μm are presented in comparison with the initial chemical composition of the alloys. Found that before and after heat treatment in the welding zone and near-weld zone particles of topologically cloth-packed phases are not observed. Balance of alloying is better maintained in deformable high-temperature disk nickel alloy EP975 and this is natural, since pressure under superplasticity conditions takes place due to the disk alloy and at cast intermetallic single-crystal alloy only diffusion processes take place. Thus, high-quality one-piece connection of a disk and a blade for blisk-type structures is feasible under superplasticity only of one deformable fine-grained disk alloy and it is relevant for blisk type constructions. Blade intermetallic alloy VKNA-25 keeps thermally stable single-crystal structure.

On the probability of formation of intermetallic compounds in dissimilar welded joints obtained by friction stir welding

The article describes the mechanisms and causes of the occurrence of intermetallic phases during friction stir welding of dissimilar joints. The nucleation and growth of intermetallic phases for a pair of dissimilar metals to be welded under comparatively favorable time and temperature conditions of the FSW is facilitated by the atomic-vacancy environment, which is responsible for the continuous atomic-structural bond and mass transfer of accumulated atoms in local regions of the welded joint with an equiaxial grain lamella-shear structure of the welded core. compounds with a concentration close to critical, combined with others in a superplastic state. In the process of forming a welded joint under the influence of a moving and rotating welding tool, the lamellae are subjected to bending and torsional stresses with simultaneous tension, causing them to generate point defects and especially a large number of various types of dislocations, triggering the formation of edge dislocations in the lamellae, which are lined up in the process into dislocation walls, dividing lamella grains into separate fragmentary subgrain boundaries, along which the processes of fragmentation and dispersion develop. This phenomenon is explained by the fact that the processes of fragmentation and dispersion of IMP lead to the composition of the nugget of the welded joint by fragments, often nano-sized fragments of various configurations, which act as hardeners of the weld nugget matrix.

Low-temperature superplasticity of ultrafine-grained near β titanium alloy

Studies of the low-temperature superplasticity (SP) of ultrafine-grained (UFG) near β alloy Ti-5Al-5V-5Mo-1Cr-1Fe at a temperature of 823 K (∼0.42 Tm) in the range of strain rates (2.0–6.9)·10−3 s−1 have been carried out. It is shown that for an UFG alloy with an average grain size of d ∼ 0.17 µm, obtained by the method of multi-axial pressing, the value of the relative elongation to failure exceeds 950% at a strain rate of 2·10−3 s−1. Annealing of the UFG alloy at a temperature of 873 K for 1 h does not cause a noticeable increase in the average grain size (d ∼ 0.23 µm), but leads to the transition of a part of grain boundaries to a more equilibrium state and a decrease in elongation to failure by more than 3 times in the range of strain rates. The study of the evolution of the microstructure under tension at a rate of 2·10−3 s−1 showed that in both states of the alloy up to an elongation of 150%, the average size of the elements of the grain-subgrain structure practically does not change, which is due, among other things, to the appearance of new grains less than 100 nm in size during the SP deformation. It is shown that the significantly lower elongation to failure of the UFG Ti-5Al-5V-5Mo-1Cr-1Fe alloy subjected to annealing may be due to the hindered accommodation of grain boundary sliding during the SP deformation by intragranular dislocation slip because of the transition of individual grain boundaries to an equilibrium state. The preservation of the UFG structure of the alloy with high strength characteristics under conditions of low-temperature superplasticity creates good prerequisites for obtaining high-strength products of complex shape in the regime of SP forming.

ANALYSIS OF THE PARAMETERS OF DYNAMIC SUPERPLASTICITY THE INDUSTRIAL ALUMINUM ALLOYS

The problem of determining the features of the development of blurred phase transitions observed under conditions of dynamic superplasticity of aluminum alloys is solved using the specific heat capacity function. Within the framework of the developed model representations, the deformation mechanisms characteristic of superplasticity and boundary metastable states are analyzed using the Fokker-Planck equation. Using a macrokinetic model, an explicit expression is obtained for the function that characterizes the mechanism of grain boundary slippage (the “drift " coefficient) that prevails in superplasticity. By integrating the differential equations resulting from the model, the solution of which establishes the type of functions responsible for the implementation of the mechanisms of grain boundary slippage and diffusion processes. It is proposed that the diffusion coefficient is responsible for the accumulation of irreversible deformations outside the velocity range of superplasticity. The function responsible for the effects of grain boundary slippage (the "drift" coefficient) is particularly active towards the middle of the superplasticity velocity interval. It is confirmed that outside the velocity range of superplasticity, there is a redistribution of mass transfer forms, the responsibility for which is assigned to the diffusion coefficient. It is shown that the diffusion function shows a tendency to decrease when approaching the range of superplasticity rates. Metastable states are characterized by the competition of diffusion mechanisms and grain boundary slippage.

Numerical/experimental investigation of bulge tests on a localized laser heat-treated magnesium alloy AZ31 sheet

Lightweight alloys can be considered among the most promising materials thanks to their capability to reduce the environmental impact, without affecting mechanical properties. In addition, when very complex shapes are required, a viable strategy could be represented by the adoption of non-conventional forming processes applied to tailored blanks that allow to obtain local variation of the material properties. In fact, referred to the Mg alloys, both grain size and temperature strongly influence the deformation behavior, as well as the mechanical properties. In this work, the effects of a selective Laser Heat Treatment (LHT) on a Mg AZ31B-H24 alloy sheet were investigated both numerically and experimentally. Experimental tests were performed, using a Diode laser source and keeping a square spot stationary in the center of the sample. The microstructure evolution was evaluated by means of light microscopy. Subsequently, the heat-treated samples were subjected to bulge tests under superplastic conditions (450°C) and using pressurized argon gas. The experimental microstructure distributions obtained were used for the numerical bulge tests analyses performed in the same conditions of the experimental trials. Experimental LHT results showed the capability to locally modify the microstructure when suitable temperatures and interaction times are selected. Regarding the bulge tests, the obtained results showed the possibility to effectively affect the thickness distribution of the final shapes.

Mechanical Properties of a Layered Ti–6Al–4V Alloy Composite Material Fabricated under Low-Temperature Superplasticity Conditions

Mechanical Properties of a Layered Ti–6Al–4V Alloy Composite Material Fabricated under Low-Temperature Superplasticity Conditions