Effect of large strain cross rolling on microstructure and properties of Al-Li alloy plates with high magnesium content

Transmission electron microscopy(TEM),electron backscattered diffraction imaging(EBSD)and X-ray diffractometry were used to analyze the microstructure and texture characteristics of Al-9.8Mg-1.5Li-0.4Mn alloy cross-rolled and extruded plates,and the tensile properties and deep drawing performance were measured.The results show that the occurrence of dynamic recrystallization was promoted,the grains were refined and the preferred orientation of the recrystallized grains was improved by large strain cross rolling.Compared with CBA and CCB rolling methods,CBB rolling method significantly reduced the orientation density of the typical Brass texture{110}?112?in the extruded plates.The orientation densities of Copper texture{112}?111?and Brass texture{110}?112?on theβorientation line in the CBB rolled plates were the lowest,and there were no typical texture features in the plates.Meanwhile,better deep drawing could be gained in the CBB rolled plates,and the mechanical properties of the 0°,45°and 90°directions were basically the same.The tensile strength,yield strength and elongation at room temperature for the CBB rolled plates were 617 MPa,523 MPa and over 20.1%,respectively.The deviation of the mechanical properties at different directions was less than 3%.

Anisotropy of mechanical properties of 2297-T87 Al–Li alloy thick plates

The tensile properties of 2297-T87 Al–Li alloy thick plates at different thickness position and in different direction were analyzed via tensile testing,optical microscopy(OM),X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectrometry(EDS),and transmission electron microscopy(TEM).Results indicated that the ultimate tensile strength(UTS)and yield strength(YS)of the alloy decreased firstly and then increased from the 1/8T position to the 1/2T position,whereas elongation to failure(Ef)decreased gradually such that its value along the rolling direction(RD)was higher than those along the transverse direction(TD)at the same thickness position.From the 1/8T position to the 3/8T position of the alloy,the UTS and YS along the TD were higher than those along the RD.At the 1/2T position of the alloy,the UTS,YS,and Ef along the RD were the highest,whereas those along the normal direction(ND)were the lowest.Microstructural observations further revealed that the anisotropy of tensile properties was related to grain morphology,crystal texture,second-phase particles,and Li atom segregation.

Impact Damage Identification of Aluminum Alloy Reinforced Plate Based on GWO-ELM Algorithm

As a critical structure of aerospace equipment,aluminum alloy stiffened plate will influence the stability of spacecraft in orbit and the normal operation of the system.In this study,a GWO-ELM algorithm-based impact damage identification method is proposed for aluminum alloy stiffened panels to monitor and evaluate the damage condition of such stiffened panels of spacecraft.Firstly,together with numerical simulation,the experimental simulation to obtain the damage acoustic emission signals of aluminum alloy reinforced panels is performed,to establish the damage data.Subsequently,the amplitude-frequency characteristics of impact damage signals are extracted and put into an extreme learning machine(ELM)model to identify the impact location and damage degree,and the Gray Wolf Optimization(GWO)algorithm is employed to update the weight parameters of the model.Finally,experiments are conducted on the irregular aluminum alloy stiffened plate with the size of 2200 mm×500 mm×10 mm,the identification accuracy of impact position and damage degree is 98.90% and 99.55% in 68 test areas,respectively.Comparative experiments with ELM and backpropagation neural networks(BPNN)demonstrate that the impact damage identification of aluminum alloy stiffened plate based on GWO-ELM algorithm can serve as an effective way to monitor spacecraft structural damage.

Influence of dent on residual ultimate strength of 2024-T3 aluminum alloy plate under axial compression

Drop-weight impact tests were conducted on 2024-T3 aluminum plates with five types of impactors, and then the effects of the dent on the residual ultimate strength of the 2024-T3 specimens were investigated through axial compression tests. Results indicate that with increase in dent depth, the five types of dents affect the ultimate strength of the plate in different trends. Nevertheless, other than the plate global deflection caused by impacting, the dent itself has unremarkable effect on the ultimate strength. The mathematical expressions are derived regarding the relationship between impact energy factor and the dent depth factor as well as the compressive ultimate strength reduction rate and the dent depth factor.

Surface quality, microstructure and mechanical properties of Cu-Sn alloy plate prepared by two-phase zone continuous casting

Cu-4.7%Sn （mass fraction） alloy plate was prepared by the self-developed two-phase zone continuous casting （TZCC） process. The relationship between process parameters of TZCC and surface quality of the alloy plate was investigated. The microstructure and mechanical properties of the TZCC alloy plate were analyzed. The results show that Cu-4.7%Sn alloy plate with smooth surface can be obtained by means of reasonable matching the entrance temperature of two-phase zone mold and the continuous casting speed. The microstructure of the TZCC alloy is composed of grains-covered grains, small grains with self-closed grain boundaries, columnar grains and equiaxed grains. Compared with cold mold continuous casting Cu-4.7%Sn alloy plate, the room temperature tensile strength and ductility of the TZCC alloy plate are greatly improved.

Relationship between microstructure and mechanical properties of 5083 aluminum alloy thick plate

The microstructure and mechanical properties of 105 mm thick 5083 aluminum alloy hot rolled plate were investigated by metallurgical microscope, scanning electron microscope and tensile testing machine, and three major characteristic problems in mechanical properties inhomogeneity were explained. The results show that the mechanical properties of the rolled plate are inhomogeneous along the thickness direction. From the surface to the center, the strength shows an inverted "N" shape change and the elongation presents a semi "U" shape change. Several similar structural units composed of long fibrous grains(LFG) and short fibrous grains bands(SFGB) exist in a special layer(Layer 2) adjacent to the surface. This alternating layered distribution of LFG and SFGB is conducive to improving the plasticity by dispersing the plastic deformation concentrated on the boundary line(BL) between them. However, their different deformability will cause the alternation of additional stresses during the hot rolling, leading to the strength reduction. The closer the location to the center of the plate is, the more likely the recovery rather than the recrystallization occurs. This is the possible reason for the unnegligible difference in strength near the central region(Layer 4 and Layer 5).

Progress of electroplating and electroless plating on magnesium alloy

The current research processes of electroplating and electroless Ni-P alloy plating on magnesium alloys were reviewed. Theoretically,the reason for difficulties in electroplating and electroless plating on magnesium alloys was given.The zinc immersion, copper immersion,direct electroless Ni-P alloy plating and electroplating and electroless plating on magnesium alloys prepared by chemical conversion coating were presented in detail.Especially,the research development of magnesium alloy AZ91 and AZ31 was discussed briefly.Based on the analysis,the existing problems and future research directions were then given.

Effect of pre-deformation of rolling combined with stretching on stress corrosion of aluminum alloy 2519A plate

The effect of the pre-deformation of rolling combined with stretching on the stress corrosion cracking resistance of aluminum alloy 2519A was studied by means of the slow strain rate technique at 10-6 s-1. The tensile strength and stress corrosion index of the alloy plate with 7% rolling plus 3% perpendicular stretching were 481 MPa and 0.0429, respectively, showing better mechanical property and stress corrosion cracking resistance than those with 4% rolling plus 3% parallel stretching or 7% rolling plus 3% parallel stretching, which is due to its finer and denser precipitates within the grains, discontinuous grain boundary precipitates, as well as more narrow precipitate-free zone width. Such microstructure is attributing to the denser and more homogeneously distributed dislocations which are produced by the pre-deformation.

Transverse stress-strain evolution during welding of thin aluminum alloy plate

The FE simulation results of transverse stresses and strains during welding of thin aluminum alloy plate are presented. The results indicate that restraint condition is the main factor that determines whether or not hot cracking will occur. With rigid restraint hot cracking (crater cracking) will occur at the arc-stopping end, and such cracking usually will not occur without external restraint. But under restraint-free condition it is easy for terminal cracks to occur.

Stress-level dependency of creep ageing behavior for friction stir welded Al-Cu alloy

Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by friction-stir welding is still a great challenge to now.In this work,the creep ageing behaviors and underlying microstructure evolution of a thick friction-stir welded Al-Cu alloy plate after CAF process under different stress levels are systematically investigated.The creep strain and the strength of the joint are both significantly increased when the stress is close to the average yield strength of the initial weld joint.The grain size reduces while the local strain and dislocation density increase from top to bottom of the NZ;hence,the bottom layer of the weld joint exhibits higher creep strain and steady-stage creep strain rate during the CAF process.The results reveal that the gradient microstructures sensitive to the stress level effectively govern the creep-ageing performance from the upper to the bottom layer in a thick friction stir welded Al-Cu alloy plate.Rationally increasing the initial dislocation density of the weld joint can both enhance the tensile properties and promote the creep deformation of the weld joint for CAF process.

Effects of Ti_(0.5)Al_(0.5)N coatings on the protecting against oxidation for titanium alloys

Ti0.5Al0.5N coatings were deposited on TC11（Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） and silicon substrates using a cathode arc ion-plating system.The microstructure, composition, phase structure, and oxidation-resistance of the alloys and nitride coatings were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, Auger electron spectroscopy, and thermal analyzer.The results show that the oxidation resistance of the titanium alloy is relatively limited;the compound structures of Ti mixed with Al oxides are formed during the heating process.The phases of the Ti0.5Al0.5N coatings are composed of a TiN solid solution phase.The oxidation kinetics obeys the parabolic law.During the oxidation process, the selective oxidation of Al occurs, thus protecting the underlying coating and substrate.

Modified Layer-Removal Method for Measurement of Residual Stress in Pre-stretched Aluminium Alloy Plate

Residual stress is one of the factors affecting the machining deformation of monolithic structure parts in the aviation industry. Thus, the studies on machining deformation rules induced by residual stresses largely depend on correctly and efficiently measuring the residual stresses of workpieccs. A modified layer-removal method is proposed to measure residual stress by analysing the characteristics of a traditional, layer-removal method. The coefficients of strain release are then deduced according to the simulation results using the finite element method （FEM）. Moreover, the residual stress in a 7075T651 aluminium alloy plate is measured using the proposed method, and the results are then analyzed and compared with the data obtained by the traditional methods. The analysis indicates that the modified layer-removal method is effective and practical for measuring the residual stress distribution in pre-stretched aluminium alloy plates.

Tensile and Microstructure for One Ti Alloy Plate

A multi-step isothermal forging and subsequent multipass rolling was used to produce one kind of two phase titanium alloy plate with thickness of 2.2 mm. Tensile properties at ambient temperature and at two kinds of high temperatures were investigated for the plate with submicrocrystalline (SMC) structure in present work. Microstructures and fractographies of the alloy plate before and after tensile tests were also observed by scanning electron microscope. The results indicated that the alloy possesses favorite integrated tensile properties at ambient temperature, the average UTS and elongation for the longitudinal sample is 1070 MPa and 20%, while which for the transverse sample is 1103 MPa and 15%. The tensile elongation of the alloy plate is as high as 1078% at 780°C with a primary strain rate of 1.7 × 10-3 s-1. The microstructure is fine for the alloy plate solutioned at 700°C for 1 h, AC, and the grain size after tensile test is 2 μm and 3 μm for the longitudinal and transverse plates. Fractography for the as-annealed plate is composed of a large number of dimples and voids after tensile test at ambient temperature.

Effect of non-uniform stress characteristics on stress measurement in specimen

There is a remarkable difference in stress distribution between a specimen and a plate removed from the specimen.The plate presents a uniform stress distribution whereas the specimen presents a non-uniform stress distribution.Firstly,the real stress distributions in plates with thickness of 30,40 and 50 mm and then in the specimens were obtained through simulation and X-ray surface stress measurement.Secondly,in order to study the impact of specimens shapes and processing ways on the results accuracy,two irregular shapes (parallelogram and trapezoid) and two processing ways (saw and electron discharge machining (EDM)) were compared and analyzed by simulation and experiment using layer removal method,then the specimen effects on measurement results were evaluated.The results show that:1) the non-uniform stress distribution characteristics of the specimen near the surface of the cut is significant,the range of non-uniform stress distribution is approximately one-thickness distance away from the cut,and it decreases gradually along the depth;2) In order to ensure the stability in the results,it is suitable to take the specimen plane size 2-3 times of its thickness;3) Conventional processing methods have little effect on experimental results and the average deviation is less than 5%.

Analysis of strain variation in cross shear zone of plate during snake hot rolling

In order to study the distribution of equivalent and shear strain of aluminum alloy plate during snake hot rolling, several coupled thermo-mechanical finite element models(FEM) are established. Effects of speed ratio and offset distance on strain distribution of the plate are analyzed. The length of cross shear zone is defined to have a better understanding of the deformation characteristic in cross shear zone, which is the essential difference from symmetrical rolling in deformation zone. The results show that the equivalent strain and shear strain of lower part both increase with the increase of speed ratio, while the upper part decreases; the equivalent strain through the whole thickness decreases with ascending offset distance, while the shear strain of lower part increases. The length of cross shear zone quickly increases with ascending speed ratio and slightly decreases with ascending offset distance. The "positive" and "negative" cross shear zones are formed with the increase of speed ratio and offset distance, respectively. The value of the sensitivity coefficient of speed ratio is an order of magnitude bigger than the offset distance. However, the shear strain at center point increases with the ascending speed ratio and offset distance for different mechanism. As speed ratio increases, the asymmetry of the distribution of equivalent is becoming larger and the shear strain is generated in the same direction in cross shear zone. The FEM results agree well with experimental results.

Biodegradable Zn-0.5Li alloy rib plate:Processing procedure development and in vitro performance evaluation

Trauma kills more than four million people worldwide each year,with chest trauma accounting for 25%of these deaths.Rib fractures are the main manifestation of chest trauma.Biodegradable Zn alloys offer a new option to overcome clinical problems caused by permanent rib fracture internal fixation mate-rials,e.g.,long-term stress masking and secondary surgery.In this study,the fabrication procedure of biodegradable Zn-0.5Li alloy rib plates is successfully developed,which consists of casting,hot-warm rolling,cutting,and pressing sequentially.Biomechanical three-point bending performance of the Zn al-loy rib plates is comparable to that of commercial pure Ti rib plates,much higher than that of pure Zn rib plates.In addition,the Zn alloy exhibits the best antibacterial ability against E.coli and S.aureus among the three materials.Although the Zn alloy exhibits a weaker MC3T3 cytocompatibility than pure Ti,it is better than pure Zn.This study provides a foundation for the future development of various biodegrad-able Zn alloy rib plates.

Aluminum Alloy Material Structure Impact Localization by Using FBG Sensors

The aluminum alloy structure impact localization system by using fiber Bragg grating （FBG） sensors and impact localization algorithm was investigated. A four-FBG sensing network was established. And the power intensity demodulation method was initialized employing the narrow-band tunable laser. The wavelet transform was used to weaken the impact signal noise. And the impact signal time difference was extracted to build the time difference localization algorithm. At last, a fiber Bragg grating impact localization system was established and experimentally verified. The experimental results showed that in the aluminum alloy plate with the 500mm＊500mm＊2mm test area, the maximum and average impact abscissa localization errors were 11 mm and 6.25mm, and the maximum and average impact ordinate localization errors were 9 mm and 4.25 mm, respectively. The fiber Bragg grating sensors and demodulation system are feasible to realize the aviation aluminum alloy material structure impact localization. The research results provide a reliable method for the aluminum alloy material structure impact localization.

Insights into microstructural evolution and deformation behaviors of a gradient textured AZ31B Mg alloy plate under hypervelocity impact

We have for the first time elucidated the microstructural evolution and deformation behaviors of a gradient textured AZ31 B Mg alloy plate under the ultrahigh strain rate of ~10~6 s^(-1) that is generated by a two-stage light gas gun with the hypervelocities of 1.6-4.4 km s^(-1). The hypervelocity impact cratering behaviors indicate that the cratering deformation of AZ31 B Mg alloy is mainly affected by the inertia and strength of the target material. The crater prediction equation of AZ31 B Mg alloy target under impact velocity of 5 km s^(-1) is given. The 2017 Al projectile completely melts in the Mg alloy target plate at the impact velocities of 3.8 km s^(-1) and 4.4 km s^(-1), and the microstructural evolution around the crater is: dynamic recrystallization zone, high-density twinning zone, low-density twinning zone, and Mg alloy matrix. It is found that the dynamic recrystallization, twinning and cracking are the main deformation behaviors for the AZ31 B Mg alloy to absorb the shock wave energy and release the stress generated by the hypervelocity impact. The main plastic deformation mechanisms of the Mg alloy target during hypervelocity impact are twinning and dislocation slip. Microstructure analysis shows the interactions of twins-twins, dislocations-dislocations, and twins-dislocations determine the strain hardening during the hypervelocity impact process, which eventually contributes the dynamic mechanical properties. The evolution of microhardness around the crater further demonstrates the microstructural evolutions and their interactions under the hypervelocity impacts.

Microstructures and properties of 6016 aluminum alloy with gradient composition

Weight reduction plays an important role in reducing fuel and emissions,and the heat-treatable 6016 aluminum alloy exhibits excellent application prospect in automobile lightweight.In this paper,ingot with constant Mg/Si ratio and decreased Mg and Si contents was obtained.Both the microstructure and the texture of 6016 aluminum alloy plate designed with different alloy compositions at the top/bottom were systematically investigated by electron backscatter diffraction technology(EBSD)measurement,as well as the room-temperature mechanical properties at the different positions with composition gradient.The results indicate that as Mg and Si contents increase,the grain size decreases,improving the cube texture with recrystallization and weakening the S texture.The strength of 6016 aluminum alloy decreases with lower Mg and Si contents.

Microstructure and Mechanical Properties in Friction Stir Welded Thick Al–Zn–Mg–Cu Alloy Plate

In this work, 20-mm-thick aluminum-alloy plates were joined via friction stir welding. The temperature gradient was reduced by reducing the surface welding heat input to achieve uniformity of the mechanical properties across the thick plate joints. The welding temperature was measured using thermocouples. The microstructures were observed via electron backscatter diff raction and transmission electron microscopy. The tensile properties of the samples sliced along the thickness direction of the joint were evaluated. The results show that the highest welding peak temperature is 430℃ on the advancing side on the top surface of the joint. The grain size gradually decreased along the thickness direction, and grain refi nement was due to the combination of continuous, discontinuous, and geometric dynamic recrystallization. The tensile properties of the sliced samples were found to be uniform, and the ultimate tensile strength reached 62% of that of the base metal. The main strengthening mechanism of the Al–Zn–Mg–Cu alloy joints consists of precipitation strengthening. In addition, the η ` → η phase transition and grain coarsening in the heat-affected zone were found to be responsible for the fracture of the joints.