The corrosion behavior and time-dependent mechanism of 22MnB5 steel featuring a thinned Al-Si coating (60 g/m2) were systematically investigated in a chloride ion wet-dry cyclic environment, motivated by the demand for thinning and toughening development of aluminum-silicon coatings. A periodic immersion accelerated corrosion test using 3.5% NaCl solution was conducted, together with macro/microscopic morphology observation (SEM/EDS), phase analysis (XRD, FTIR), and electrochemical measurements (polarization curves, EIS). The Al-Si coated steel was studied over corrosion periods of 1, 8, 10, and 20 days to elucidate its corrosion behavior, interfacial evolution, and failure mechanism. The results indicated that the corrosion process exhibited a three-stage evolution: stable protection, rapid failure, and dynamic equilibrium. At the initial stage (1 day), a dense Al2O3 passive film formed on the coating surface, providing excellent substrate protection, with a corrosion current density of only 1.77 & micro;A/cm2 and a maximum charge-transfer resistance (R2) of 652 Omega & centerdot;cm2. In the middle stage (8 days), Cl- permeated through the cracked film, triggering selective dissolution of Al, while Si was enriched in situ to form a porous residual layer; the corrosion current density (Icorr) sharply increased to 13.25 & micro;A/cm2, and R2 dropped to its minimum of 156.6 Omega & centerdot;cm2. Corrosion products at this stage were mainly Al2O3 and SiO2, accompanied by small amounts of iron oxyhydroxides and hydroxides, and local coating failure began to appear. During the later stage (10-20 days), the corrosion products evolved into gamma-FeOOH, alpha-FeOOH, and Fe2O3, which, together with an amorphous SiO2 gel network enriched at the interface, formed a dual-layer composite rust layer. R2 consequently recovered from 156.6 Omega & centerdot;cm2 at 8 days to 424 Omega & centerdot;cm2 at 20 days, indicating a reduced corrosion rate and entry into a stable inhibition stage. The critical failure mechanism is that Cl- preferentially penetrates the surface of the Al2O3 passive film, disrupting the metastable state of the coating and thereby creating pathways for corrosive media intrusion. The findings of this study can provide technical support for the safe application of such as-received coatings in non-load-bearing components with heat and corrosion resistance requirements.

The Al-Li alloy has the advantages of low density, high specific strength, good weldability, good fracture toughness, strong fatigue crack propagation resistance, and excellent corrosion resistance. However, the plasticity of Al-Li alloy is poor at room temperature, so it formability is not ideal. In order to solve the problem, the electric pulse-assisted forming test is carried out on the 2A97-T3 Al-Li alloy to explore the forming properties. The mechanism of the forming perfoemance is revealed by the stress-strain curve macroscopically and the microstructure morphology microscopically. The results show that the Joule heating effect and the electron wind effect are generated in electric pulse-assisted forming. As a result, the yield strength and the tensile strength of the 2A97-T3 Al-Li alloy are significantly reduced. The Joule heating effect is enhanced due to the large pulse current intensity at the necking part, which can easily cause overburning. The grain size increases due to overburning. The elongation at break decreases significantly. After conducting a certain number of electric pulse-assisted forming tests, the appropriate processing parameters are obtained as follows: the pulse current intensity is 450 A, the duty cycle is 60.0%, the frequency is 50 Hz, and the forming rate is 0.001 s-1. The yield strength of Al-Li alloy is 89 MPa, and the elongation to fracture is 13.2% under that condition. The formability is obviously improved. Besides, the dynamic recovery and the dynamic recrystallization of the alloy occur.

The 2A97 Al-Li alloy has been used in some key structural parts of aircraft to achieve lightweight. However, coordinating control of the forming performance and the forming accuracy is difficult. The above problems can be solved by the hot forming with synchronous quenching (HFSQ) process. The HFSQ process is simultaneously carried out hot forming and quenching in the mold; then, the forming part is pressed for some time. And the forming accuracy of the HFSQ part is predicted through the finite element simulation. The accuracies of formed parts of the cold forming, the new quenching forming, and the HFSQ are compared. Through the comparison of the finite element simulation and the test results, it is proved that the HFSQ process is the best. The flatness of the formed part is 0.1248, the maximum size deviation between the long and the short bend distances is 0.14 mm, and the angling error is within the range of ± 0.7°. The tensile strength and the yield strength of the undeformed and deformed portions of the HFSQ parts are higher than those of the original alloy. The microstructures and the precipitates of the HFSQ part are characterized. The average diameter of the microstructure of the original alloy is 28.54 μm. The average diameters of the undeformed and deformed parts of the HFSQ parts are 22.59 μm and 24.86 μm, respectively. And the grain sizes are refined. The phases of the T1 and the δ' are mainly strengthening phases in the undeformed zone. And the T1 phases are fine needle-like in the deformation zone. The forming quality and the accuracy of the 2A97 Al-Li alloy are significantly improved by the HFSQ process. Therefore, coordinating control of the forming precision and the performance of the 2A97 Al-Li alloy has been achieved through the HFSQ process.

The 2A97 Al-Li alloys have been used in aircraft to achieve lightweight, its high cycle fatigue performance is one of the important factors that determines aircraft safety. The 2A97-T8 Al-Li alloy is obtained through the 2A97-T3 Al-Li alloy undergoes the hot forming with synchronous quenching process. The 2A97-T3 and 2A97-T8 Al-Li alloys are tested for high cycle fatigue under different stress amplitudes. The fatigue crack propagation path of the 2A97-T3 Al-Li alloy is not only along the direction of maximum shear stress at 45 degrees to the stress direction but also along the direction perpendicular to the stress axis. The fatigue crack propagation path of the 2A97-T8 Al-Li alloy propagates along the direction perpendicular to the stress axis. Under high amplitude stress, the characteristics of quasi-cleavage fracture are found in the fracture morphology of 2A97-T3 AlLi alloy. However, the characteristics of cleavage fracture are found on the fracture morphology of 2A97-T3 Al-Li alloy under low amplitude stress. Under high amplitude stress, the quasicleavage characteristics and the dimples are found on the fracture morphology of 2A97-T8 AlLi alloy. Under low amplitude stress, the small voids and the dimples are found on the fracture morphology of 2A97-T8 Al-Li alloy. The precipitated phases of the 2A97-T3 Al-Li alloy are multitudinous, fine, and dispersed delta' phases and a few T1 phases. The precipitates of the 2A97-T8 Al-Li alloy are large, fine, and acicular T1 phases and a few delta' phases. The hot forming with synchronous quenching process significantly improves the high cycle fatigue properties of the 2A97 Al-Li alloy. In addition, the fatigue cycles, the fatigue life rise and fall plots, the S-N curves, and the fatigue crack growth behaviors of the 2A97-T3 and 2A97-T8 Al-Li alloys are obtained.

This study presents a novel tube-forming method that employs a pulsed laser as a stamping tool to form a small-diameter bulged tube, which could not be easily obtained via conventional tube forming. A mechanism for the dynamic forming of a laser-induced micro-bulge was introduced, and an analytical model was developed to analyze the micro-bulging deformation induced by single laser irradiation. A finite element model was also built to simulate shock wave propagation and the dynamic progress of tube expansion. A series of validated deformation experiments were conducted. The study findings showed that the laser-induced shock wave diffused rapidly, causing the tube to expand at the shocked zone. When subjected to a one-shot laser shock, the tube underwent deformation with micro-bulging. The application of a confining layer was found to be beneficial for tube deformation. The magnitude of the tube deformation increased with the increase of laser shots. Moreover, as the laser pulse energy increased, the bulge deformation of the tube also increased. The proposed process provides an efficient alternative to form the expansion tube with a smaller diameter in the future.

The spring steel for automotive stabilizer bars has a great responsibility in that its quality directly affects the stability, safety, and comfort of vehicle operation. The isothermal thermal compression behavior of a novel lean Si spring steel that was used to manufacture an anti-roll bar was investigated with a DIL805A/D quenching thermal dilatometer in this research. A hyperbolic sine type of constitutive model was established, and hot processing maps were produced to evaluate the experimental steel’s hot workability properties. The experimental results suggest that dynamic recrystallization (DRX) preferentially occurs at a low strain rate and high thermal processing temperature, while the processing maps of the experimental steel are susceptible to strain. The instability regions increase as the strain increases. The processing maps’ stable and instable domains should be decided upon comprehensive analysis of the instability criterion, power dissipation efficiency, and strain rate sensitivity index. The optimum parameters of hot processing for the experimental steel at various strains are that the deformation temperature of 1000–1150 °C and the strain rate of 0.1, approximately.

以Co基Stellite6合金与陶瓷(WC)为熔覆粉末,采用激光熔覆技术在沉没辊 316L基体添加质量分数为 60%的WC粉末,制备Stellite6-60WC熔覆层,分析激光功率、扫描速度、送粉量等工艺因素对熔覆层形貌的影响,确定最优熔覆工艺参数;且对复合涂层的物相、硬度和耐磨性进行研究,探讨熔覆层高温耐磨性能改善的机理.结果表明:激光功率 1.5 kW、扫描速度300 mm/min、送粉速率 18.8 g/min时,熔覆层表面质量较好,涂层与基体形成良好的冶金结合,表面无裂纹和孔洞;熔覆层的相组成主要为γ-Co,M7C3,M23C6(M=Co,Cr,Fe),W2C等硬质相,利于提高熔覆层的硬度,硬度可达 736.2 HV,是基体的3.5倍;熔覆层的高温耐磨性优于316L基体,比基体提高了6.1倍,主要是熔覆层多种硬质强化相及未熔的WC颗粒所致.

为了提高5052铝合金在应用中的安全性,准确的计算结构件在复杂载荷下的强度,非常有必要对材料在不同应变率下的力学性能进行研究.本文分别采用高温电子万能试验机和霍普金森拉杆装置对其进行了准静态和高应变率下的拉伸试验,得到了材料的应力-应变曲线,构建了能够准确描述其塑性变形行为的本构模型.结果表明:5052铝合金具有明显的应变率敏感性,且随着应变率的增加,其屈服强度和强度极限不断增加.基于试验结果,本文提出采用一种修正的Johnson-Cook模型来拟合材料的动态本构关系,拟合结果与试验数据吻合度较高;进一步使用ANSYS软件用此模型模拟了高应变率下试样的单向拉伸过程,提取典型节点的应力应变曲线,模拟结果与试验结果相吻合.说明本文所建立的修正Johnson-Cook模型能够较好地描述5052铝合金的动态特性,可为实际工程中的数值模拟问题提供数据支持,从而为零部件的加工工艺、结构设计和实际生产提供可靠的参考和有效的指导.

This study focuses on the effects of the key process parameters during a modified hydrodynamic deep drawing utilizing a combined floating and static die cavity (HDDC). A two-stage hydraulic loading path is recommended in the novel process, and each stage of the hydraulic loading path is a linear loading path with an inflection point. The method to evaluate the wrinkle and forming dimension precision of the formed parts is introduced at first. Then, the influence of the key parameters of the two-stage hydraulic loading path as well as the blank holder force on the dimension accuracy and surface quality of the formed parts was studied in detail. The results showed that the influence of the liquid pressure during the second stage is more significant than that in the first stage in hydrodynamic deep drawing utilizing a combined floating and static die cavity. The initial pressure of the second stage and the maximum pressure arriving moment during this stage have a significant impact on the dimensional accuracy of the formed parts, and the smaller initial pressure or the later the maximum pressure of the second stage arrives, the higher the accuracy of the formed part is. Similarly, the influence of the blank holder force in the second stage on the forming accuracy is more significant than that in the first stage.

The competition mechanism of ferritic recrystallization and austenitic transformation, nucleation and growth kinetics of different crystallographic orientation components during intercritical annealing of a cold-rolling Fe–Al–Mn–Mo–C deep drawing dual-phase steel were investigated by a series of continuous annealing simulation experiments. The experiments provided an insight into the microstructural characteristics and mechanical behaviors that were caused from the interaction of primary recrystallization and phase transformation. The results show that the promoting effect of austenite transformation is greater than that of ferrite recrystallization with the increase of temperature in the two-phase region, and an appropriate soaking time is contributed to the formation and development of {111} oriented grains. Austenite formation affects morphology and size of the microstructure owing to inhibiting ferrite recrystallization and growth. From these that experimental data of the observed temperature or time-dependent mechanical properties can be interpreted. An excellent comprehensive properties with tensile strength of 480 MPa and plastic strain ratio (r value) of 1.15 can be obtained at annealing temperature of 880 °C for 300 s.

Dual phase steel generally has poor deep drawing property with a low r value less than 1.0, making it difficult to be used for deep drawing automotive parts. In order to improve the mechanical properties of the steel through heat treatment, effect of heat treatments with different conditions on a Fe-Si-Cr-Mo-C deep drawing dual-phase steel was investigated with the aim of identifying effective heat treatment parameters for effective modification towards optimal properties. Relevant thermal dilation and heat treatment experiments were performed. Corresponding characters were investigated. The results show that island martensite can be obtained at low cooling rate. With the increase of cooling rate, the formation of pearlite and bainite is favored. During annealing at low temperatures, recrystallization of the steel is incomplete with the presence of the shear bands. With the increase of annealing temperature, the recrystallization process is gradually complete, and the number of high angle grain boundaries increases significantly. The ratio of gamma orientation components to alpha orientation components decreases first and then increases with the increase of annealing temperature. The strain hardening exponent and r value show an upward trend with respect to annealing temperature, and the r value is as high as 1.15.

为改善成形件的表面质量和壁厚均匀性,提出双层板渐进成形方法.以典型圆锥件为研究对象、5052铝合金板为目标板、304不锈钢板为辅助板,实验分析成形件的表面粗糙度和壁厚分布,探讨辅助板对成形件表面质量及壁厚均匀性的影响.结果表明:单层板和双层板渐进成形件表面质量差异明显,在目标板厚度≥0.6 mm的条件下,双层板渐进成形可获得表面质量更好的零件;辅助板厚度对成形件表面粗糙度也有影响,合适的辅助板厚度可改善成形件壁厚分布均匀性,增大最小厚度.

以成形件不同高度截面上实测直径与目标直径的差值作为翻边精度的判据,研究5182-O铝合金板材三道次圆孔渐进翻边中工艺参数对翻边精度的影响.结果表明:初始成形角对圆孔翻边件精度影响显著,较小的初始成形角可保证第二、三道次成形时有足够的变形,成形件每道次成形后的实测直径与目标直径偏差逐渐减小,进而得到精度较高的圆孔渐进翻边件;工具头层压下量对成形件直径偏差影响很大,层压下量大于一定值时,渐进成形过程中工具头和板料接触部位完全位于变形区和未变形区分界线未变形板料一侧,当工具头继续渐进挤压板料时,变形区带动附近成形区继续变形,造成变形区尺寸变大,使最终成形件尺寸变大,甚至产生成形件尺寸正偏差现象.

A Ti bearing interstitial-free steel was finishing rolled in the ferrite region with and without lubrication and microstructures, mechanical properties and textures evolution during warm rolling and subsequent annealing were investigated by OM, SEM, tensile test and ODF. The results show that the surface microstructure of the as-rolled specimen without lubrication is composed of dense shear bands, while the microstructures of the central layer of the as-rolled specimen without lubrication and the whole cross section of the as-rolled specimen with lubrication are elongated ferrite. Short-time annealing can make the non-lubricated rolling sample recrystallize, but the lubricated rolling sample cannot. After complete recrystallization, the microstructure of the surface layer of the as-annealed specimen without lubrication is finer than that of the center layer of the as-annealed specimen without lubrication and the whole section of the as-annealed specimen with lubrication. The mechanical properties of as-annealed sample without lubrication change significantly in the initial annealing stage, while that of as-annealed sample with lubrication remain unchanged until the end stage of annealing. The surface layers of the as-rolled samples have strong Goss component and weak γ fibre components, while the central layers have strong γ fibre components and moderate rotated cubic components. As annealing proceeds, the Goss components of the surface layer decrease and the γ fibre components increase. The rotated cubic components in the central layer are gradually transformed into γ texture.

This paper presents the method to shape a deep conical cup with multi-step laser shocking forming. Finite element method was employed to simulate the process of three-step laser shocking forming (TSLSF), and the process of sheet deformation at each step was analyzed. Especially, sheet deformation behaviors including deforming velocity, strain, residual stress, and geometrical shape were discussed in detail. The sheet-forming experiments were carried out to validate the simulation results. The numerical predictions of the deformed sheet shape in each step were compared and discussed with the corresponding experimental forming values. The experimental results display that three geometrical cups have been fabricated by TSLSF. The experimental results are well accordance with the corresponding numerical predicted data, which validates the established prediction model of sheet forming. It also indicates that MSLSF is a feasible forming process when the flat sheet needs to be formed into a deep-depth workpiece.

In this study, industrial trial production of the microstructure evolutions and resultant mechanical properties and finite element model of the temperature variation in the cryogenic temperature rebar subjected to the TempCore processes were presented. The microstructure of tested steel rebar is composed of ferrite, pearlite and bainite when the cooling rate is less than or equal to 5 degrees C s(-1). The pearlite disappears when the cooling rate is 10 degrees C s(-1), and the microstructure is composed of granular bainite and a small amount of ferrite. The microstructure consists of martensite and bainite at cooling rate of 20 degrees. Compared with the tested steel rebar with water flow rate of 450 m(3)h(-1), the tested steel rebar with water flow rate of 100 m(3)h(-1) has an optimum mechanical strength and a higher uniform elongation at room temperature, and has a higher NSR(notch sensitivity ratio) at -165 degrees C. The uniform elongation is 7.3% at room temperature and NSR is 1.14 at -165 degrees C. The ductile-brittle transition temperature of the tested steel rebar with water flow of 100 m(3)h(-1) is about -30 degrees C, while which of 450 m(3)h(-1) is 0 degrees C. The impact energy of the tested steel bar with water flow of 100 m(3)h(-1) is 2 similar to 3 times that of 450 m(3)h(-1) at or below 0 degrees C, which is mainly due to its ultrafine acicular ferrite and bainite containing high dislocation density and sub-grains.

During the drawing process, when the radial tensile stress is greater than the limit of the sheet metal's bearing capacity, the workpiece will rupture. In order to succeed in forming the cylindrical part, it is necessary to reduce the radial tensile stress, or even change the tensile stress into compressive stress. In the current study, electromagnetic pulse-assisted incremental drawing (EMPAID) technology was used to form the cylindrical part, which can generate magnetic force on the flange material, which pushes them to flow into the die cavity. The drawing coil with different turns matching the determined corner coil and different auxiliary coils were used to conduct the experiments. When the two-turn drawing coil, one-turn corner coil, and two-turn auxiliary coil were used, after multiple times of discharge and micro-shaping, the limit of the drawing height of the formed part increased to 42.86mm, which was 2.16 times of the limit drawing height obtained using the conventional drawing. Using the three-turn drawing coil combined with the corner coil and four-turn auxiliary coil to carry out the experiments, the cylindrical part's maximum drawing height reached 63.72mm. Meanwhile, the flange area was almost completely converted into the cylinder wall. When the dense winding auxiliary coil was used to conduct the experiments, the maximum forming depth was only 25.24mm. The experimental results showed that during the forming process, majority of the flange material was pushed into the die cavity due to the action of magnetic force. Due to this reason, the thinning of the forming part can be suppressed. If the magnetic force generated by the drawing and auxiliary coils matched reasonably, then the depth of the formed part can be improved significantly.

Two laser-induced shock wave pressures, 4.5 and 6.5GPa, were applied to punch LC4CS aluminum sheet respectively, and the influence of different pressures on fracture behaviors was investigated. The code ANSYS/LS-DYNA, dynamic finite element software, was employed to investigate the sheet fracture behaviors during the punching process. The experimental results display that the punching quality manufactured by higher peak pressure of shock wave is better than that by lower one. The finite element method visualizes the punching process, including sheet deformation, cracks growth, and plug flying away. The computational analysis results reveal that the time to punch the sheet with higher peak pressure of shock wave is shorter than that with lower one, and the edge of punched hole resulted from the higher peak pressure is smoother than that from the lower one, which are consistent well with the experimental results.

采用充液拉深筒形件再液压胀形的复合液压成形工艺成形环形件,利用DYNAFORM5.9软件对环形件复合液压成形过程进行模拟,探究不同工艺因素下预成形筒形件对环形件成形质量的影响,因素包括拉深比、最大液压、凸模圆角半径及中间退火.结果表明:随着拉深比增大,筒形件和环形件的最薄点壁厚逐渐减小;采用单拐点液压加载的筒形件充液拉深成形中最大液压愈大,得到的环形件壁厚减薄愈剧烈,最薄点壁厚愈小;随着凸模圆角半径的增加,筒形件圆角处壁厚增加,胀形后环形件最薄点壁厚减小;在复合液压成形的两工序间对筒形件进行中间退火,有利于后续加工,提高成形性能.