Alloy Thick Plate Research Articles

Effect of ageing process on microstructure and properties of 2124 aluminum alloy thick plate

Effect of ageing process on microstructure and properties of 2124 aluminum alloy thick plate

Abnormal fracture of 7085 high strength aluminum alloy thick plate joint via friction stir welding

7xxx series high-strength aluminum alloy joints by friction stir welding (FSW) generally fracture in the heat affected zone (HAZ), i.e. the lowest hardness zone (LHZ) during tensile test. However, the experiment results of this study indicate that defect-free FSW joints of 7085-T7452 aluminum alloy thick plate fracture in the weld nugget zone (WNZ) instead of the HAZ for the whole joint or the top slice exhibits very low strength and elongation when using a high rotational rate of 600rpm. Both the microstructure characteristics and the microhardness distribution are not main reasons for the abnormal fracture in WNZ for the whole joint and the top slice. WNZ-top presents both the lowest average Taylor factor and the largest area fraction of grains with high strain. Moreover, the significant strain is concentrated in WNZ-top, showing the inhomogeneous deformation, for the whole joint or the top slice with the increase of nominal stress. But no strain concentration is presented in WNZ-middle and WNZ-bottom and the strain increases uniformly in HAZ for the middle and bottom slices. Combined actions of the above three factors lead to the characteristic of preferential intergranular fracture in WNZ for the whole joint and the top slice.

A new approach to deformation control of aeronautical monolithic components of aluminum alloy plates based on stress inverse and stress evaluation

In the high-speed machining process of aeronautical monolithic component, the release of residual stresses is a crucial factor of machining deformations with the material removal of 7075 aluminum alloy thick plates. Therefore, the investigation on the evolution mechanism of machining deformation with residual stress release is crucial for machining quality control. It is vital to achieving a high-efficiency and precise machining process. In this work, the bending deformation theory is employed to formalize the mechanical model of machining deformation, which is influenced by the removal of materials. The finite element method is used to calculate the unit deformations by producing the unit stresses in each layer of the aluminum alloy thick plate. The unit force method is established so that the mechanical model of machining deformation can decompose to be multiple of deformation factor with residual stress. Further, by considering the self-equilibrium of residual stresses, the specification model of residual stresses is proposed based on the fact that the machining requirement represents the control limit of machining deformation. By introducing a new unit variable, the sandwich theorem is employed to convert the specification model into the linear homogeneous inequalities. Therefore, the pivot transformation method is suggested to solve the residual stresses in the specification model. Finally, by representing an arbitrary variable as a difference between two non-negative variables, the linear programming method is proposed to judge whether the measured blank initial residual stress is a solution of stress specification. This can evaluate machining deformation within the machining requirement. The active evaluation of residual stresses, which is deduced from the passive analysis of machining deformations by unit force method and pivot transformation, can provide the proper stress specification for the upper of the machining process. Obviously, the stress specification plays a very important role in the bridge between the blank manufacturing and the machining process.

Through-thickness inhomogeneity of precipitate distribution and pitting corrosion behavior of Al–Li alloy thick plate

Abstract The thorough-thickness inhomogeneity of precipitate distribution and pitting corrosion behavior of 95 mm-thick 2297 Al−Li alloy rolled plate was investigated using scanning electron microscopy, transmission electron microscopy and electrochemistry method. Precipitate distribution and pit size were statistically analyzed to obtain quantitative information and corresponding correlation. The population density and the size fraction of precipitate on different sections in the thick plate are ranked from high to low in the following order: quarter-section (QS) > surface section (SS) > mid-section (MS). After 300 min potentiostatic polarization, the number and the total volume of pits are ranked from high to low as QS>SS>MS, indicating a higher pitting susceptibility of the plate in QS with more precipitates. The through-thickness inhomogeneity of pitting corrosion in 2297 Al−Li alloy thick plate is mainly ascribed to inhomogeneous precipitate distribution.

Investigation on microstructure and mechanical properties of cold source assistant friction stir processed AZ31B magnesium alloy

Magnesium alloys subjected to friction stir processing usually exhibit undesirable mechanical properties due to their intense basal texture throughout the processed zone. In this work, cold source assistant friction stir processing was innovatively conducted on AZ31B magnesium alloy to modify the microstructure and mechanical properties in the plate thickness direction. The results showed that liquid CO2 has a high cooling efficiency, which can prevent grain coarsening and activate the {10–12} twinning behavior in the surface region, resulting in an ultra-refined grain structure with abundant twin boundaries. The {10–12} twins reduced basal texture intensity, and thus the contribution of grain boundary strengthening and second phase strengthening in the strength and hardness modification became more obvious. {10–12} twin boundaries can also enhance the dislocation storage capacity, resulting in the well-matching of the ultimate tensile strength and elongation. This work provides a simple and effective surface modification strategy to enhance the hardness and strength of a magnesium alloy without ductility loss. Additionally, it also gives an idea for manufacturing a gradient structure in magnesium alloy thick plate.

Effect of Intermediate Thermomechanical Treatment on Microstructure and Mechanical Properties of 2A97 Al-Li Alloy

Effect of intermediate thermomechanical treatment on tensile properties at short-transverse direction, fracture mechanism and microstructure of 2A97 Al-Li alloy thick plate were studied by tensile testing, SEM, EBSD and TEM.The results show that with the increasing of compression deformation, the strength and elongation of the alloy increase first and then decrease slightly. The fracture mode of the alloy changes from quasi-cleavage fracture to high energy ductile fracture. When the compression deformation rises to 20%, the elongated structure are replaced by a more uniform and equiaxial structure. The distribution of δ phase distribute more homogeneously in the grains.

Effect of average pass reduction ratio on thickness-oriented microstructure and properties homogeneity of an Al–Zn–Mg–Cu aluminum alloy thick plate

The influence of hot rolling average pass reduction ratio (APRR) on thickness-oriented microstructure and properties homogeneity of an Al–Zn–Mg–Cu aluminum alloy thick plate has been studied by mechanical properties, fracture toughness together with optical microscope, scanning electron microscope and electron backscattered diffraction microstructural examinations. Results show that the strength and fracture toughness were remarkably increased with the increase of APRR, and the thickness-oriented non-homogeneity of yield strength and fracture toughness were reduced by 38% and 36.5%, respectively. The significantly improvement of thickness-oriented homogeneity of strength and fracture toughness of alloy with higher APRR was attributed to the weaker shear texture, lower volume fraction of recrystallized grains and smaller constituent particles size.

Quench sensitivity of Al–Cu–Mg alloy thick plate

The quench sensitivity of Al–Cu–Mg alloy was investigated at different thicknesses of the thick plate. The quenching process was simulated via finite element analysis (FEA); time–temperature–property (TTP) curves and time–temperature–transformation (TTT) curves were obtained through hardness test and differential scanning calorimetry (DSC) test; and the microstructural observation was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Experimental results exhibit that the quench cooling rate decreases dramatically from the surface to the center of the plate, and the inhomogeneous quenching causes the difference in microstructure. With the decrease in quench cooling rate, constituent particles are coarsening gradually; the quantity of T-phase (Al20Cu2Mn3) increases and the S-phase (Al2CuMg) decreases. According to the precipitation kinetics analysis, the decrease in S-phase is caused by the increase in precipitate activation energy. So that the center of the plate shows the highest quenching sensitivity, which is consistent with the analysis of time–temperature–property curves and time–temperature–transformation curves.

Some aspects regarding the influence of the anisotropy of an AA2021-T351 rolled thick plate on its tribological behaviour

This scientific paper aims to study the influence of the anisotropy of an aluminium AA2024-T251 rolled thick plate on the surface tribological properties based on previous experimental and numerical studies concerning bulk and surface mechanical behaviour. Experimental friction tests have been made on the aluminium alloy thick plate surface using sliding of an ultra-high-molecular-weight polyethylene (UHMWPE) cylindrical pin. The used tribological test involves the generation of local motion along specified trajectories with different orientations under the action of a constant normal force and a constant slip velocity. Three different normal forces (3N, 5N, 7N) have been applied using five different sliding speeds (0.005, 0.05, 0.5, 1 and 5mm/s) along a linear trajectory of 3 mm length. In order to analyze the influence of the aluminium alloy anisotropy, the tests have been performed along three directions: a longitudinal one, corresponding to the rolling direction of the sample (0°), a transverse one, perpendicular to the rolling direction (90°), and a median direction (45°). Taking into account the observed bulk and surface anisotropy, especially concerning a fractal nature of the surface topography, an investigation was performed in order to determine its influence on the anisotropic tribological properties. In this purpose, fractal friction characteristics have been determined for the sliding process using a constant normal force Fn = 7N and the above five sliding speeds.

Mechanical behavior of 7085-T7452 aluminum alloy thick plate joint produced by double-sided friction stir welding: Effect of welding parameters and strain rates

Mechanical behavior of double-sided friction stir welding (DS-FSW) aluminum alloy thick plate joints under various rotational rates and welding speeds tested at different strain rates were investigated. The results show that both the yield stress (YS) and the elongation to failure of DS-FSW joints increase, but the ultimate tensile strength (UTS) of defect-free joints decrease with the decrease of strain rate from 10−2 s−1 to 10−5 s−1. A remarkable reduction in the YS, UTS and elongation to failure presents, particularly at the top slice of 950/60 joint, reaching approximately 65%, 68% and 25% of the BM tested at a strain rate of 10−4 s−1and fails through brittle fracture. The top slice presents the highest strength and the middle slice has the largest ductility, the same as change laws of joint efficiency and strain hardening behavior among three slices. The best welding parameters is the rotational rate of 300 rpm and welding speed of 60 mm/min due to the higher and the smaller fluctuation of strength and ductility for different slices.

Effect of Welding Speed on Fatigue Properties of TC18 Thick Plate by Electron Beam Welding

The welding of 15 mm thick TC18 titanium alloy thick plate was realized by electron beam welding. The effect of different welding speeds (10, 20, 30 mm/s) on the fatigue properties of the electron beam welded joints for TC18 titanium alloy was investigated. The macroscopic morphology, microstructure and fracture characteristics of the joints were analyzed by optical microscope, scanning electron microscopy and transmission electron microscopy, and the fatigue properties of welded joints were studied and tested by an electronic universal testing machine. The results show that the weld fusion zone is mainly composed of columnar β phase and acicular α martensite phase. The upper melting width, the middle melting width and the lower melting width are obviously reduced, and the grain size gradually decreases with the increase of welding speed, which results in the increase of fatigue properties of welded joints. At Nf =107 the fatigue limit of the weld increases by nearly 29% with the welding speed from 10 mm/s to 30 mm/s. The fatigue fracture of the joints can be divided into three typical regions of fatigue crack source zone, expansion zone and instantaneous zone, and the fatigue cracks all originate from the surface of the specimen. With the increase of welding speed, the proportion of instantaneous area decreases and the fatigue performance increases.

Effect of Overaging on Fatigue Crack Propagation and Stress Corrosion Cracking Behaviors of an Al-Zn-Mg-Cu Alloy Thick Plate

The fatigue property as well as stress corrosion cracking (SCC) resistance of an Al-Zn-Mg-Cu alloy thick plate in peak-aged and overaged tempers (T7351 and T7651) is systematically investigated by fatigue crack propagation (FCP) test and slow strain rate test (SSRT). Microstructural characterization is examined by transmission electron microscopy and scanning electron microscopy. Results reveal that the T7351 alloy has lower strength but higher electrical conductivity as compared to T7651 alloy. The FCP resistance of T7351 alloy is superior to that of the T7651 alloy due to the coarser precipitates in the highly overaged alloy in which the strain localization is reduced by promoting homogeneous slip. In addition, the SSRT test suggests a higher SCC resistance in T7351 alloy. The enhanced SCC resistance is found to depend on grain boundary precipitate characteristics and crack propagation resistance of the alloys.

Microstructure and Properties of Welded Joint of 6063 Aluminum Alloy Medium and Thick Plate

In this paper, the welding parts of the 6063 aluminum alloy 15mm and 20mm plate on the solar wing expansion frame of a certain type of satellite are studied. The structure of the welding structure is analyzed and tested. The relationship between the distribution characteristics of the joint and the mechanical properties of the weld and the influence law of the weld are analyzed, and the welding process is rationally formulated in the actual production. Provide theoretical basis and technical support for improving welding quality. The two thickness aluminum plates are formed by MIG welding. The metallographic samples and tensile specimens are intercepted from the welded parts, and the metallographic samples are prepared. The microstructure and tensile strength and hardness of the welded joints are analyzed by metallographic microscope, scanning electron microscope, X ray diffractometer, tensile test machine and microhardness tester. Degree. The results show that there is a softening zone in the welded joint, which mainly exists in the heat affected zone; at the same time, there will be a high hardness point (15mm 84.6HV; 20mm 70HV) in the fusion zone, which is due to the presence of more strengthening phase Mg2Si and a small amount of Al12Mg17. The average tensile strength of the welded joint with two thickness is 166MPa and 218MPa respectively, and the thickness of 15mm is lower than the tensile strength of 6063 aluminum alloy, while the 20mm thickness is higher than the theoretical tensile strength of 6063 aluminum alloy, and the elongation is higher than that of the 6063 aluminum alloy theory, in which the joint of 15mm thick welded joint is pulled from the 15mm at the weld seam. Extension fracture, 20mm thick welded joint tensile fracture at the weld.

Prediction of properties distribution of 7B50 alloy thick plates after quenching and aging by quench factor analysis method

In the present work, continuous cooling curves were accurately measured by the modified Jominy specimen of 7B50 alloy during water-spray quenching tests. Besides, the time–temperature–properties (TTP) curves of this alloy were obtained during isothermal treatments. Based on the accurate cooling curves and TTP curves, the hardness distribution along the thickness direction of 7B50 alloy thick plates was predicted by quench factor analysis method. It is found that the quench sensitive temperature range of 7B50 alloy is 240–410 °C, the nose temperature is 335 °C, and the incubation period at the nose temperature is about 0.87 s. When 7B50 alloy was isothermal treated at 180–400 °C after solid solution treatment (470 °C for 1 h followed by 483 °C for 2 h), the exponent (n) in the Johnson–Mehl–Avrami equation is close to 1 until transformed fraction of new precipitates is up to 60%, indicating that new precipitates first grow into rodlike shape and then coarsen or thicken. When the distance is less than 65 mm from the spray quenching surface of the modified Jominy specimen, the deviation between the predicted and measured hardness is less than 2.7%, confirming the quench factor analysis method as the feasible way to predict the hardness distribution along the thickness direction of 7B50 alloy thick plates. When the distance from the spray quenching surface is 25 mm, the average cooling rate in quench sensitive temperature range is 9.93 °C·s−1, while the quench factor (τ) is 9.89 and the corresponding predicted hardness is HV 185.1 equivalent to 97.3% of the maximum measured hardness of 7B50 alloy in T6 temper.

Formation mechanism and prediction of plane shape in angular rolling of aluminum alloy thick plate

A finite element model (FEM) was developed to study the plane shape of an aluminum alloy thick plate after angular rolling. Results show that the plane shape is a parallelogram after the first pass of angular rolling. When the angular rolling process is completed after a second pass, the plane shape becomes symmetric about the center lines in both length and width directions. The width increases more at the edge that enters the deformation zone earlier. Next, a mathematical model to predict plane shape after angular rolling was proposed based on a sectional calculation method. By simulating the longitudinal rolling process, spreads from different plate widths were obtained and used in the mathematical model. By comparing these results with results from the FEM, the accuracy of the mathematical model was verified. Because of its short calculation time, the mathematical model can be used in practice during the production process.

Relationship between the weld pool convection and metallurgical and mechanical properties in hybrid welding for butt joint of 10-mm-thick aluminum alloy plate

The ALHW and LAHW processes are applied to join 5083 aluminum alloy with thickness 10 mm; the differences of weld pool convection is studied, and the relationship between the weld pool convection and microstructural characterization of aluminum alloy in ALHW and LAHW processes are analyzed. The result shows that an inward flow pattern, furious mingling, and stirring effects in LAHW process will contribute to a better weld bead with lower porosity level. The shorter escaping route of the bubble, more difficult bubble captured, and better stability of the keyhole are the three effective factors for eliminating of porosity. In LAHW process, the grain size is larger, but the LAHW joints have higher tensile strength, which is greatly influenced by porosity and second-phase particles. Compared with ALHW process, the LAHW process is beneficial to get the less weld defects, better bead formation, and higher tensile strength, which is conducive to successfully weld aluminum alloy thick plates potentially.

Evolution of the 3D plastic anisotropy of HCP metals: Experiments and modeling

A two-surface, pressure-insensitive plasticity model is further developed to represent the mechanical response of hexagonal close packed metals. The model describes the 3D plastic anisotropy of a material, the tension–compression asymmetry, and the consistent evolution upon straining of both the net anisotropy and the asymmetry. The model may be viewed as a reduced order quasi-crystal plasticity model whereby the two activation surfaces represent glide- and twinning-dominated flow. The two-surface formulation enables to represent independent, yet coupled, hardening laws in terms of effective plastic strains accumulated on either generic deformation system. Application of the model to a discriminating data set assembled for a magnesium alloy thick plate illustrates the capabilities and versatility of the modeling approach.

Electron beam welding of laser additive manufacturing Ti–6.5Al–3.5Mo–1.5Zr–0.3Si titanium alloy thick plate

Individually fabrication parts by laser additive manufacturing (LAM) and then jointing them together through electron beam welding (EBW) is a viable way for manufacturing large components with reduction of internal stress. For investigating the microstructure and mechanical property of EBW joint along longitudinal and transverse direction in LAMed component, two LAMed Ti–6.5Al–3.5Mo–1.5Zr–0.3Si plates were successfully welded without defects. Results show that the microstructure of base metal (BM) is a typical basket-weave morphology that exhibits lamellar α within β matrix. In heat affected zone (HAZ), the part of primary α transforms to β with the some very fine lamellar αs precipitates out. Due to the fast solidification rate, a large number of acicular α′ forms in fusion zone (FZ), leading to the highest microhardness. All tensile samples fail in BM region with the fracture type of intergranular dimpled fracture. Compared with the T-joint, the L-joint shows higher ultimate tensile strength and yield strength, but lower elongation and reduction of area due to the morphology of columnar grains and the strong texture of β<010> parallel to the deposition direction.

Microstructure evolution in the conventional single side and bobbin tool friction stir welding of thick rolled 7085-T7452 aluminum alloy

The microstructure evolution during the conventional single side friction stir welding (SS-FSW) and the bobbin tool FSW (BB-FSW) of 7085-T7452 alloy thick plate was extensively studied by using the state-of-the-art materials characterization techniques. The Electron backscattering diffraction results reveal that a significant grain refinement and a larger percentage of high angle grain boundaries (HAGBs) exist in the weld nugget zone (WNZ) and the thermal-mechanical affected zone (TMAZ) compared with the base material. Meanwhile, more obviously inhomogeneous refined grains and HAGBs in WNZ along the thickness direction and a larger percentage of low angle grain boundaries (LAGBs) were observed in SS-FSW joint than that in BB-FSW joint. The change of the average grain size is the result of friction heat and strain rate of plastic deformation combined with a certain degree of recrystallization. Moreover, the recrystallization is mainly controlled by the strain rate during the FSW process. The presence of Cube and Cube ND after welding shows that the discontinuously dynamic recrystallization (DDRX) is a major factor in the final microstructural response. The research and findings help the understanding of the mechanism of microstructure homogenization and further optimizing the welding process for application.

Analysis of deformation characteristics and microstructure variation of thick plate during asymmetric shear rolling

Aluminium alloy thick plate is widely used in field of aerospace and automobile industry for its light weight, high strength, good corrosion resistance and formability. Hot rolling is the key process of preparation for thick plates, however, the conventional symmetrical rolling process causes large deformation on the surface and small deformation in the central portion of the thick plate, resulting in inhomogeneous deformation, microstructure and property distributions through the thickness direction of the plate. Asynchronous rolling is beneficial for deformation permeation into the central part of thick plate with introduction of strong shear strain due to velocity asymmetry of two work rolls. However, the plate will bend towards the slower roll due to deformation asymmetry at upper and lower surface of the plate and serious bending is bad for multi-pass rolling process. Asymmetrical shear rolling with velocity asymmetry and geometry asymmetry is adopted in this study. Compared to asynchronous rolling, there is a horizontal offset distance of upper roll in outlet direction. A moment will be applied to the plate in the opposite direction of bending towards the slower roll by an offset distance of the slower roll. The comparisons of distributions of equivalent strain, temperature, DRX fraction and average grain size between symmetrical rolling and asymmetrical shear rolling are studied. The effects of velocity asymmetry and offset distance on microstructure variation and microstructure distribution at different positions of the plate are studied. Due to larger velocity of lower work roll, larger equivalent strain and higher temperature appear at lower layer of the plate, which results in higher DRX fraction and finer grain size. The speed ratio contributes greatly to sufficient DRX process and finer grain size; while the ascending offset distance decreases the DRX fraction. Therefore, speed ratio plays significant role in deformation permeation and grain refinement in asymmetrical shear rolling and the offset distance is mainly used to decrease the bending behaviour of the plate. This study can provide guidance to thick plate preparation with good properties in asymmetrical rolling process.