一种整体壁板填料辅助滚弯成形过程中填料作用机理

研究一种2A12铝合金整体壁板的聚丙烯填料辅助滚弯成形工艺,结合力学分析、数值模拟和实验验证,揭示填料的作用机理。结果表明,整体壁板筋条与蒙皮处的中性层位置差导致其成形后母线直线度不达标,填料可以降低这种中性层位置差。当填料与筋条有一定宽度间隙(1~3 mm)时,可以避免填料卷曲和筋条失稳。而填料和筋条的高度间隙决定填料可被压缩程度,当填料在压缩后仍高于筋条(1 mm)时,可以达到最佳的压力传递效果。填料的弹性模量在一定范围内时(450~1300 MPa),对整体壁板的成形精度影响不大。但填料弹性模量较低时(50 MPa),填料传递的压力不足;填料弹性模量较高时(20 GPa),整体壁板弯曲变形受限。实验后壁板母线直线度的测量结果验证了填料的作用机理。

Analysis of inhomogeneity of solidified microstructure of continuous casting copper tubular billet based on factor analysis

The horizontal continuous casting process,the initial step in TP2 copper tubular processing,directly determines the microstructure and properties of copper tubular.However,the process parameters of the continuous casting characterize time variation,multiple disturbances and strong coupling.As a consequence,their influence on a casting billet is difficult to be determined.Due to the above issues,the common factor and special factor analysis of the factor analysis model were used in this study,and the casting experiment and billet metallographic experiment were carried out to diagnose and analyze the reason of the microstructure inhomogeneity.The multiple process parameters were studied and classified using common factor analysis,2 the cast billets with abnormal microstructures were identified by GT^(2) statistics,and the most important factors affecting the microstructural homogeneity were found by special factor analysis.The calculated and experimental results show that the principal parameters influencing the inhomogeneity of solidified microstructure are the primary inlet water pressure and the primary outlet water temperature.According to the consequence of the above investigation,the inhomogeneity of the copper billet microstructure can be effectively improved when the process parameters are controlled and adjusted.

Dynamic globularization prediction during cogging process of large size TC11 titanium alloy billet with lamellar structure

The flow behavior and dynamic globularization of TC11 titanium alloy during subtransus deformation are investigated through hot compression tests. A constitutive model is established based on physical-based hardening model and phenomenological softening model. And based on the recrystallization mechanisms of globularization, the Avrami type kinetics model is established for prediction of globularization fraction and globularized grain size under large strain subtransus deformation of TC11 alloy. As the preliminary application of the previous results, the cogging process of large size TC11 alloy billet is simulated. Based on subroutine development of the DEFORM software, the coupled simulation of one fire cogging process is developed. It shows that the predicted results are in good agreement with the experimental results in forging load and microstructure characteristic, which validates the reliability of the developed FEM subroutine models.

Microstructure and properties of TP2 copper tube with La microalloying by horizontal continuous casting

The TP2 copper tube was prepared with La microalloying by horizontal continuous casting(HCC). The absorptivity of La and its effects on microstructure, tensile and corrosion properties of HCC TP2 copper tube were studied by means of the inductively coupled plasma optical emission spectrometer(ICP-OES), optical microscope(OM), scanning electron microscope(SEM) and potentiodynamic polarization measurements. The results show that the absorptivity of La in the HCC TP2 copper tube is about 15% under antivacuum conditions due to the good chemical activities of La. The impurity elements in copper tube such as O, S, Pb and Si can be significantly reduced, and the average columnar dendrite spacing of the copper tube can also be reduced from 2.21 mm to 0.93 mm by adding La. The ultimate tensile strength and the elongation with and without La addition are almost unchanged. However, the annual corrosion rate of the HCC TP2 copper tube is reduced from 10.18 mm·a^(-1) to 9.37 mm·a^(-1) by the purification effect of trace La.

Evolution of Goss texture in thin-walled copper tube at different heat treatment temperatures

The evolution of microstructure,textures,and mechanical properties of thin-walled copper tube during heat treatment was investigated using EBSD technique and tensile test.The results show that the initial deformation textures of pre-drawn thin-walled copper tube are mainly composed of Copper and Y components,while with the increase of temperatures,the textures are transformed into a strong Goss texture gradually.The high-resolution microstructural characterizations indicate that the new Goss recrystallized grains nucleate and grow up within the deformed Copper grains and Y grains in different mechanisms,respectively.The tensile strength of the thin-walled copper tube decreases gradually with the increase of the temperature,while the elongation increases first and then decreases sharply due to the action of grain sizes and texture components.

Effect of δ Phase on Mechanical Properties of GH4169 Alloy at Room Temperature

Tensile tests of GH4169 alloy were performed at room temperature. Different fractions, distributions and shapes of δ phase was prepared by aging treated at 880 ℃, 930 ℃ and 980 ℃ for 5 h or 10 h. The effect of δ phase on the mechanical pro- perties of GH4169 alloy was investigated. The results show that 0.2% yield strength and ultimate tensile strength of GH4169 alloy increase by 61 MPa and 78 MPa respectively when the fraction of δ phase increases from 2.20% to 5.21%. Then, the ultimate tensile strength remains at 1 012 MPa even when the fraction of δ phase reaches 7.56%. The fraction effect of δ phase on the strength improvement of GH4169 alloy is more significant than morphology, and the critical fraction value is 5.21%. In addition, the elongation decreases by 14.1% when the fraction of δ phase increases from 2.20% to 7.56%. Excessive needle or short rod shaped 8 ohase is resoonsible for the reduction of eloneation.

Evolution of Annealing Twins and Recrystallization Texture in Thin-Walled Copper Tube During Heat Treatment

Thin-walled copper tubes are usually produced by multi-pass float-plug drawing deformation.In general,the annealing treatment subsequently is necessary to release the stored energy and adjusts the microstructure.In this study,an investigation on the evolution of annealing twins as well as textures in the thin-walled(Φ6 mm×0.3 mm)copper tube underwent holding time-free heat treatment was reported.Electron backscattered diffraction analysis reveals that a large number ofΣ3 boundaries(600<111>twin relationship)are produced at the early stage of heat treatment,which is due to the lower boundary energy.With the recrystallization proceeding,the migration rate of grain boundaries decreases on account of the grain growth;meanwhile,the uniqueΣ9 boundaries(38.9°<110>relationship)are formed due to the interaction of theΣ3 boundaries.As a result,the number fractions ofΣ3 boundaries and high-angle grain boundaries decrease rapidly.During the grain growth stage,a strong recrystallization texture was formed due to the fact that the grains of Goss orientation have a growth advantage over the others.As a result,the initial copper texture was transferred into the Goss texture in domination.

Influence of delta phase precipitation on static recrystallization of cold-rolled Inconel 718 alloy in solid solution treatment

Due to the improvement in fatigue strength of cold-rolled blades,the static recrystallization behavior of cold-rolled Inconel 718 alloy in the solid solution treatment was investigated with the methods of optical microscopy and electron backscattered diffraction.The effect ofδphase precipitation on the static recrystallization process was also analyzed.The results show thatδphase preferentially precipitates comparing to static recrystallization.Affecting by theδphase preferential precipitation process,sub-grain migration is the main nucleation mechanism in the static recrystallization of coldrolled Inconel 718 alloy at 980°C.Meanwhile,strain-induced boundary migration also exists as an aided nucleation mechanism when the rolling reduction is less than 30%.

Texture modification and mechanical properties of AZ31 magnesium alloy sheet subjected to equal channel angular bending

Analysis of the recently proposed equal channel angular bending(ECAB)process is provided on thin hotrolled AZ31 magnesium alloy sheets.In particular,effects of deformation temperature and strain path on the texture evolution and mechanical properties are systematically investigated under single pass ECAB at various temperatures and multi-pass ECAB process that involves changes in strain paths.It is found that simultaneous activation of multiple twinning types is successfully introduced during ECAB,which results in obvious tilted component of basal texture.Attributed to the domination of extension twins,weaker basal textures are detected after both single pass ECAB at 150℃and three cross passes ECAB at 200℃.After annealing,the basal texture is further weakened via twin-related recrystallization and the annealed microstructure is featured with mixture of basal and non-basal orientated grains.Additionally,the effect of grain orientation on the mode of plastic deformation and the roles of grain orientation and grain boundary on the local strain accommodation are coherently studied.This study reveals that over 60%increase of uniform elongation with marginal reduction of tensile strength less than 5%can be achieved for single pass ECAB at 150℃and three cross passes ECAB at 200℃,which is the result of larger fraction of grains favored with extension twinning and better local strain accommodation.

Deformation Mechanism of AZ31B Magnesium Alloy Under Different Loading Paths

Deformation and texture evolution of AZ31 B magnesium（Mg） alloy sheet under uniaxial tension, compression, and reverse loading after different pre-strain（compression and tension） were investigated experimentally. The results indicate that the pre-compressive strain remarkably affects the reverse tensile yield stress and the width of the detwinning-dominant stage during inverse tension process. Similar to stress–strain curve of the uniaxial compression, the curve of reverse tensile yield value also has ‘S＇ shape, and its minimum value is only 38 MPa. The relationship between pre-compressive strain and the width of detwinning-dominant stage presents a linear growth, and the greater the precompressive strain is, the smaller the strain hardening rate of the detwinning-slip-dominant stage is. Compared with the reverse tension under pre-compression, the influence of the pre-tension deformation on the deformation mechanism of subsequent compression is relatively simple. With the increase in pre-tension strain, the yield stress of the reverse loading is rising.

Developments of New Sheet Metal Forming Technology and Theory in China

Developments of new sheet metal forming technology and theory in China are reviewed in detail in this paper.Advances of crystal plasticity on the deformation mechanism of Mg alloy are firstly described, especially its applications on the prediction of sheet forming process. Then, a new macroscopic constitutive model is introduced, which possesses an enhanced description capacity of tension/compression anisotropy and anisotropic hardening. In order to take into account the twinning process of hexagonal close-packed material, a modified hierarchical multi-scale model is also established with adequate accuracy in a shorter computational time. The advanced forming limit of sheet metal, mainly about aluminum alloy, is also investigated. Besides the above theory developments, some new sheet metal forming technologies are reviewed simultaneously. The warm forming technology of Mg alloy is discussed. New processes to form sheet parts and to bend tubes are proposed by using hard granules. On the other hand, a new kind of ultra-high-strength steel based on typical22 Mn B5 by introducing more residual austenite and Cu-rich phase to increase the elongation and strength and its novel forming method that integrates hot stamping and quenching participation are proposed. Progresses in sheet hydroforming,press forging and electromagnetic forming of sheet metal parts are also summarized.

Twinning and detwinning during compression–tension loading measured by quasi in situ electron backscatter diffraction tracing in Mg–3Al–Zn rolled sheet

Twinning and detwinning are the important deformation modes in magnesium alloys during cyclic loading at room temperature. To analyze these two deformation mechanism, cyclic compression–tension experiments were performed on Mg–3Al–1Zn rolled sheet along the rolling direction. In these tests, the microstructure evolutions of a series of grains during deformation were traced by using quasi in situ electron backscatter diffraction(EBSD). Important quantities like the Schmid factors of twinning system, the fraction of twinning during compression, and the fraction of twinning after reverse loading were calculated on the basis of measured quantities. The influence of Schmid factor of twinning variants on detwinning upon reverse loading was analyzed. Detwinning would prefer to proceed during reverse loading if the Schmid factor of twinning in the twinning area before reverse loading is sufficiently large.

Healing Behavior of Micropores in Powder Metallurgy 316L Stainless Steel during Hot Forging and Heat Treatment

The healing behavior of micropores in powder metallurgy （P/M） 316L stainless steel during hot forging and subsequent heat treatment was studied. The results showed that hot forging can improve the homogeneity of the pore size and enhance the relative density of material in varying degree due to different forging temperatures. As a re- sult of deformation and diffusion bonding at high temperature, the irregular pores were spheroidized and finally turned into stable inner grain pores. The comparison of compression behavior between P/M and wrought dense mate rials has shown that the pores can either be the obstacles of dislocation movement or be the nucleation sites accelera- ting the reerystallization according to the difference of deformation temperatures.