Plastic Flow Of Metals Research Articles

The Preliminary Exploration of Micro-Friction Stir Welding Process and Material Flow of Copper and Brass Ultra-Thin Sheets.

In the friction stir welding (FSW) of ultra-thin dissimilar metal sheets, different physical material properties, the reduction of plastic metal in the weld zone, and insufficient plastic metal flow lead to poor weld seam shapes and joint qualities. Therefore, it is necessary to study the flow behavior during the FSW of ultrathin sheets. In this study, micro friction stir welding (μFSW) was conducted and analyzed for the butt welding of 0.6-mm-thick ultrathin brass (H62-H) and pure copper (T2-Y) sheets. By analyzing the electric signals of the temperature and force during the welding process, testing the mechanical properties, and analyzing the metallography of the joint, the influences of the process parameters on the metal flow behavior during μFSW were studied. In the proper process conditions, the material preferentially migrated and concentric vortex flow occurred in the vicinity of the shoulder and tool pin action areas. The copper was pushed from the retreating side (RS) to the advancing side (AS) of the weld, allowing it to flow more fully. A mixture of both materials formed at the bottom of the weld nugget, and less migration occurred in the heat-affected zone of the AS at this time. The highest tensile strength can reach 194 MPa, accounting for 82.6% of the copper. The presence of brittle phases Cu5Zn8, AgZn3 and AgZn caused the hardness to fluctuate slightly.

Quality improvement of bobbin tool friction stir welds in Mg-Zn-Zr alloy by adjusting tool geometry

The bobbin tool friction stir welding (BTFSW) technique was applied to a Mg -Zn- Zr alloy, ZK60-T5. The effects of shoulder diameter and stir pin geometry on the macrostructure, microstructure and mechanical properties of the BTFSW joints were studied. Weld quality was sensitive to the interaction of bobbin tool geometries and processing parameters. The reduction in the shoulder diameter led to less frictional contact and resistance and hence lowered the mechanical load imposed on the tool. The employment of the tapered stir pin reduced the traversing force, which displaced substantially less plasticized metal during the BTFSW than the cylindrical stir pin. The welding speed for the BTFSW was increased benefiting from these mechanical load alleviations. The visual aspects of the BTFSW joints, characterized by limited tunneling and voiding phenomena occurring were improved with the increase in welding speed. The BTFSW resulted in extensive softening in the stir zones of the joints due to dissolution of the β 2 ´precipitates. The tensile properties of the joints were inferior to those of the base metal due to the crystallographic isotropy in the stir zone. The improvements in tensile properties of the BTFSW joint were achieved through texture tailoring by adding threads on the stir pin. The complicated plasticized metal flow introduced by the threaded stir pin provided a randomized crystallographic texture in the stir zone which contributed to the preferable tensile properties.

An Analysis of Solid-State Electrodeposition-Induced Metal Plastic Flow and Predictions of Stress States in Solid Ionic Conductor Defects

The use of inorganic solid-ionic conductors with a metal electrode, has been proposed as a way to increase energy density, decrease capacity loss and prevent failure from metal propagation. Current observations of Li-metal electrodes causing cell shorting in solid-state systems have been identified as main obstacles limiting the development of this technology. However, many aspects of the involved phenomenon have not been fully addressed theoretically. In this work, we derive a mathematical model of electrodeposition-induced plastic flow in metal/inorganic solid-conductor systems. We use a semi-analytical solution to derive pressure increase expressions at metal protrusions and assess the possibility of fracture. The results give flow solutions analogous to laminar channel flow. The solutions also show how taking into account a boundary traction potential from built up pressure, leads to ionic redistribution and effectively screens isolated flaws, making local current focusing an incomplete explanation for observed electrolyte fracture. We show that the boundary traction potential sets a maximum value for the pressure increase that can occur from deposition at an isolated flaw. We derive conditions under which fracture can occur, and quantify the role of ionic conductivity and electrolyte fracture toughness in extending safe operating regimes of solid-state electrolytes with metal electrodes.

Взаимосвязь решеточных и деформационных характеристик среды при пластическом течении металлов

Взаимосвязь решеточных и деформационных характеристик среды при пластическом течении металлов

Numerical simulation of hot forging process in production of axisymmetric automobile parts

The finite element method and the DEFORM software were used for the plastic metal flow prediction of ring shaped parts. Various parameters that affect the forging operation are the material characteristics like material strength, ductility, deformation rate, temperature sensitivity and frictional characteristics of the workpiece, preform design, die design and die material. Numerical simulation has been done for axisymmetric automobile parts. The procedure of numerical modeling contains all simulations phases like the movement of preform from inductor to the tool, placement and setting of preform piece inside the tool before the blow in order to get as good result as possible. These techniques are used to reduce the amount of input material for forgings, extend the lifetime of forging dies, and prevent defects in forged components.

Effect of the progressive tool wear on surface topography and chip formation in micro-milling of Ti–6Al–4V using Ti(C7N3)-based cermet micro-mill

Abstract Titanium alloy is extremely difficult to machine due to the rapid tool wear. The influence of tool wear on surface topography and chip formation, during micro-milling of Ti-6Al-4V, using the Ti(C7N3)-based cermet micro-mill is investigated. The non-uniform surface quality was generated by alternative material removal mechanisms, at the cross-section of micro-slot. Metal debris and plastic side flow were more severe as the tool wear progressed, while the improved surface quality, at the up-milling side, could be obtained relative to the down-milling side. The micro-chips serration was formed, while the transition from the α-Ti to the β-Ti in micro-chips occurred as the tool wear progressed, due to the high strain and strain rate.

Microstructural evolution and mechanical properties of refill friction stir spot welded alclad 2A12-T4 aluminum alloy

Refill friction stir spot welding (RFSSW) was applied to join the 2A12-T4 aluminum alloy successfully, and effects of the tool rotational speed on weld formation, microstructure evolution and mechanical properties of the RFSSW joint were investigated in detail. There existed macrostructure characteristics of bonding ligament and hook associated to the plasticized metal flow in the joint. The microstructure of the joint exhibited variations in the grain size, precipitates distribution and substructure in the width direction. A softened region existed in all the RFSSW joints and its formation could be attributed to the coarsening and dissolution of the S precipitates. Liquation cracks associated to the localized melting of S were observed in the stir zone of the joint produced at the highest rotational speed. The tensile-shear properties of the RFSSW joints were dependent on the hook geometry, distribution of the bonding ligament and hardness of the stir zone. With increasing the rotational speed from 900 to 1300mm, the hook height increased, the bonding ligament at the weld periphery got more dispersed and the hardness of the stir zone decreased. The optimized RFSSW joint was obtained when the rotational speed was 1300rpm, and the corresponding tensile-shear failure load was 10,030N. Two different fracture modes, i.e. the shear fracture mode and shear-plug fracture mode, were identified in the tensile-shear tests.

Loading path dependent distortional hardening of Mg alloys: Experimental investigation and constitutive modeling on cruciform specimens

The forming process of Mg alloys is strongly affected by the anisotropic mechanical behavior due to crystallographic texture. Traditionally, the anisotropic behavior is captured by uni-directional loadings along different directions (e.g. Rolling Direction, RD, Transverse Direction, TD and 45∘ from RD directions). However, two more important factors have been ignored. Firstly, the subsequent deformation behavior and plastic flow of metals are determined by the whole evolution of mechanical behavior along all dimensions (i.e. σxx, σyy, σzz, σxy, σyz and σzx) instead of uni-directional mechanical property. Secondly, since the metal forming process is under multi-axial instead of uni-directional loading, the anisotropic plastic flow behavior of metals under multi-axial loading are crucial to the forming technology. Clearly both factors cannot be clarified by traditional uni-directional loading tests. In line with the state of the art progress in Elasticity and Plasticity theory at finite strain, the aforementioned factors can be clarified by the anisotropic evolution of yield surfaces, i.e., distortional hardening. For wrought Mg alloys, the anisotropic evolution of yield surfaces in σxx and σxy space for extruded bar of Mg alloys has been clarified in [1]. As a series work, the evolution of yield surfaces of AZ31 rolled sheet in σxx and σyy space under uniaxial tension was probed experimentally by means of compressive and biaxial tensile tests with specifically designed non-proportional strain paths. The anisotropic evolution of yield surface is observed under uniaxial tension, and the underlying deformation mechanism is discussed based on microstructure and texture analysis. It is found that the yield surface evolution is ascribed to dislocation hardening and texture rotation induced by basal slip with biaxial in-plane tension. A thermodynamically consistent constitutive model at finite strain is employed to capture the anisotropic behavior. The anisotropic evolution of yield surfaces of AZ31 rolled sheet under uniaxial loading along RD and TD directions are predicted and validated after model parameters identification.

Design and experimental study on full-metal sealing structure of mandrel-type casing hanger

To avoid the failure of mandrel-type casing hanger, this article provides a new type of metal sealing structure, and the sealing is achieved through plastic flow of soft metal and elastic deformation of matrix. A finite element analysis model for sealing performance of mandrel-type hanger is established to study the deformation and contact pressure of sealing cone. Among the four sealing structures studied in this article, the elliptic surface is the optimal. It is suggested to design smaller equal cone angle of inner cone angle ( β) and outer cone angle ( α) in the limited space as far as possible so as to obtain larger average contact pressure. These findings can provide references for the structural design of the seal area of the mandrel-type hanger. The sealing test results show that the sealing curve turns to be a straight line under water pressure and air pressure of 140 MPa. The results of theoretical study and laboratory experiment show that the sealing structure of full-metal multilevel conical elliptical surface is reliable and can meet the sealing requirements of the oil field wellhead device under limit working condition of 140 MPa.

Influencing surface plastic flow in metals using common chemical media

ABSTRACTWe demonstrate a unique mechanochemical effect – change in surface plastic flow by action of chemical media such as inks and glues – in large-strain deformation of metals. Unlike other well-known phenomena such as stress corrosion cracking and liquid metal embrittlement, the effect is not catastrophic and is largely material independent. High-speed in situ imaging shows that the media influence the flow by effecting a local ductile-to-brittle transition – from unsteady, large-amplitude, plastic folding, to repeated fracture and segmentation – with large decrease in deformation forces. The benign nature of the media offers opportunities for enhancing performance of metal cutting and deformation processes.

Investigation of the Portevin-Le Chatelier effect in metals under additional vibration impact by using the DIC-technique and the IR-analysis

In the present work, the deformation processes and local heating were analyzed by the digital image correlation technique and the infrared thermography accordingly to characterize the spatial-time inhomogeneity associated with the Chernov-Lüders behavior and the Portevin-Le Chatelier (PLC) effect in metals. To estimate the influence of the additional vibration impact on the serrated flow, the set of flat dog-bone specimens and thin-walled cylindrical specimens were deformed in tension with a biaxial servo-hydraulic testing system Instron 8850 and with additional vibration impact provided with a tensile load and a frequency of 4 Hz with a sinusoidal waveform. The results show the influence of additional cyclic loading on the spatial-time inhomogeneity of the plastic flow in metals, it is reduced the quasi-periodic character of the plastic flow.

Possibilities of joining different metallic parts of structure using friction stir welding methods

Abstract The transportation industry, particularly the automotive and aviation sectors, has strongly committed to reducing the mass of the construction. The process of reducing weight of a vehicle/aircraft is mainly conducted by replacing steel components by lightweight materials such as aluminum and magnesium alloys. This work presents the results of research work on linear FSW butt and lap joining of aluminum 2024-T3 and magnesium AZ31B alloys, and RFFSW joints of 5182 aluminum sheets. An analysis of microstructure and mechanical properties of FSW joints based on plastic flow and stir of metal in joint zone, thin sheets in particular, has been presented. The experimental work was conducted in laboratory and industry environments. The durability of obtained joints has oscillated around 80-90% compared to parent materials.

2D-simulation of Nanopowder High-Speed Compaction

The paper concerns the nanopowder high-speed, $10^4$ - $10^9$ s${}^{-1}$, compaction processes modeling by a two-dimensional granular dynamics method. Nanoparticles interaction, in addition to known contact laws, included dispersive attraction, formation of a strong interparticle bonding (powder agglomeration) as well as the forces caused by viscous stresses in the contact region. For different densification rates, the "pressure vs. density" curves (densification curves) were calculated. Relaxation of the stresses after the compression stage was analyzed as well. The densification curves analysis allowed us to suggest the dependence of compaction pressure as a function of strain rate. It was found that in contrast to the plastic flow of metals, where the yield strength is proportional to the logarithm of the strain rate, the power-law dependence of applied pressure on the strain rate as $p\propto v^{1/4}$ was established for the modeled nanosized powders.

Unstable plastic deformation in bimetal

The present work aims the characterization of different types of waves generated upon the plastic flow in single-crystal metals and alloys. The propagation of new types of waves is highlighted during the linear work hardening and easy glide stages of flow. As found, the motion velocity of waves is the inverse function of the work hardening coefficient.

Elastoplastic Flexure of Round Steel Beams. 2. Residual Stress

Residual stress in metals may lead to shaping defects and the failure of metal structures in prolonged operation. It may arise on account of plastic metal flow on shaping (as in forging) or slow irreversible creep at elevated temperature, under the prolonged action of loads. In viscoelastic media, it may be due to ductile strain accumulating when a body is in a deformed state for a long time. Residual stress also affects the microstructure of metals and may be present within and around crystalline grains as residual microstress, sometimes known as latent elastic stress. Residual stress is also described as eigenstress, by analogy with the eigenfunctions introduced by mathematicians to denote functions corresponding to specific parameters (eigenvalues) in a differential equation with specified boundary conditions. The concept of internal stress has been proposed as a general term for stress created by the body itself. Residual stress is then confined to cases in which the internal stress is due to irreversible deformation. Besides the creation of a favorable residual stress system, local increase in strength will be noted in forged metal disks with pronounced strain hardening, as long as the Bauschinger effect does not cancel out such benefits. In the present work, extremal values of the residual stress in a straight cylindrical steel rod (beam) are studied, in the case of flexure.

High-performance aluminium foam sandwich prepared through friction stir welding

The aluminium foam sandwich (AFS), prepared through the traditional adhesive or brazing methods, usually exhibits a low flexural strength due to the poor combination among the face sheets and the aluminium foam core. In this work, a new method, named friction stir welding (FSW), was utilized to fabricate AFS. The results demonstrated that the joining of the face sheets and aluminium foam was achieved through the plasticized metal flow. In addition, the AFS prepared through FSW possessed high flexural strength and impact resistance, as well as good sound absorption and reduction performance. This demonstrated that the FSW was a good method to prepare AFS.

The Correlation between Characteristics of Macrolocalized Plastic Deformation and Parameters of the Electronic Structure of Metals

The correlation between lattice characteristics of a deformed medium and parameters of autowaves of a localized plastic flow in metals at the stage of linear strain hardening is considered. Such correlation testifies for the existence of a close connection between elastic and plastic deformations of the medium and, more generally, between characteristics of plasticity and electronic structure of elements.

On the Certification of Positive and Convex Gotoh’s Fourth-Order Yield Function

Gotoh proposed in 1977 a fourth-order homogeneous polynomial of three plane stress components as a yield function to model anisotropic yielding and plastic flow of sheet metals. The yield function admits up to eight experimental inputs from uniaxial tension tests and one measurement from an equal biaxial tension test for calibrating its nine material constants and can model the formation of up to eight ears in deep cup drawing. However, the superior Gotoh’s yield function has not been widely adopted in sheet metal forming analyses in both academy and industry, especially outside Japan. One major concern is uncertain about the positivity and convexity of a calibrated Gotoh’s yield function. Here the problem of certifying a calibrated Gotoh’s yield function to be strictly positive and convex is first described and its resolutions are summarized based on some very recent research results. Algebraic necessary and sufficient conditions for a positive and convex Gotoh’s yield function with only two non-zero stress components are first presented. Sufficient conditions in terms of semi-algebraic and algebraic inequalities for establishing the positivity and convexity of tri-component plane stress Gotoh’s yield function are then summarized. Finally, the complete necessary and sufficient conditions for a positive and convex Gotoh’s yield function in plane stress are realized as a fully numerical minimization problem. Examples of successfully applying those conditions in certifying positive and convex Gotoh’s yield functions of various sheet metals are also given.

Kinetics of Macrolocalization Patterns of Plastic Flow of Metals

The features of the macroscopic inhomogeneity of plastic deformation in the form of autowaves with a pulsating amplitude are analyzed, and data on the localization of sources of acoustic emission at different stages of plastic flow in the stretching of fcc mono- and polycrystals are presented. The relationship between the local components of the plastic distortion tensor in the strain localization zone is traced. The role of acoustic phenomena accompanying the localization of plastic strain in the development of the process of plastic deformation is considered.

LOADING REGIME OPTIMIZATION FOR HIGH-SPEED IMPACT EXTRUSION OF BIMETALLIC FLAT-STEP ROD PRODUCTS

The work presents a physicomechanical model developed for calculating the force action on the punch with high-speed impact extrusion of bimetallic stepped rod products under conditions of plane deformation. In order to obtain the result, the process of impact loading of the workpiece is divided into two stages – acceleration and braking. At the acceleration stage, a linear dependence on the graph P n (h n ) “force on the punch – the deformation line” is adopted. For the braking stage, a procedure is given for calculating the force acting on the punch with the plastic flow of the bimetallic workpiece in a stepped narrowing cavity with three deformation centers. Based on the method of upper evaluation for the case of plastic flow at the final stage of the process, an equation is derived for calculating the force acting on the punch through deformation centers. By solving the problem in a quasistatic formulation (the action of dynamic tensions on the surfaces of velocity discontinuity and inertia forces does not affect the type and shape of the velocity and acceleration hodographs constructed), starting from the condition of the minimum power of plastic shaping, the dependences for calculating the optimum angles of the matrix cavity α опт , β опт , γ опт depending on the stretching λ and the coefficient of friction μ were determined. The use of a matrix with the optimum taper angles will allow us to realize the process of high-speed impact extrusion with minimum load acting on the punch. On the basis of the developed model, an equation for calculating the minimum upper force P n,min acting on the punch under high-speed impact plastic flow of metals through the deformation centers was obtained within the framework of the adopted assumptions. The equation presents the rheological characteristics of the deformed main part of the workpiece (k, ρ), technological parameters (λ 1 , λ 2 , λ 3 , V), contact friction coefficients μ for different parts of the surface of the matrix cavity, the impacting masses of the punch and the workpiece. The developed model for calculating the optimal power regime and equation can be used in engineering practice to develop a technology for high-speed impact extrusion of flat-step bimetallic products for various purposes.