Effect of asymmetric rolling process on the microstructure,mechanical properties and texture of AZ31 magnesium alloys sheets produced by twin roll casting technique

Symmetric rolling(SR)and asymmetric rolling(ASR)processes were carried out on 6 mm thick AZ31 magnesium alloy sheets that were produced by twin roll casting(TRC)technique.Before rolling processes,sheets were heat treated in order to obtain a homogenized microstructure.In this study,for the ASR process the rolling speed ratio between upper roller and lower was selected as 1.25.Both SR and ASR processes were utilized with 40%reduction per passes using 2 pass schedule for a total reduction ratio of 0.67.Symmetric and asymmetric rolled sheets were characterized using optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM)techniques.Texture measurements were performed by using X-ray diffraction(XRD)technique and mechanical properties were investigated by tensile tests and also hardness measurements.

Three-Dimensional Analysis of Rolling by Twin Shear Stress Yield Criterion

Using the twin shear stress yield criterion, the surface integral of the co-line vectors, and the integration depending on upper limit, Kobayashi＇s three-dimensional velocity field of rolling was analyzed and an analytical expression of rolling torque and single force was obtained. Through redoing the same experiment of rolling pure lead as Sims, the calculated results by the above expression were compared with those of Kobayashi and Sims formulae. The results show that the twin shear stress yield criterion is available for rolling analysis and the calculated results by the new formula are a little higher than those by Kobayashi and Sims ones if the reduction ratio is less than 30%.

NUMERICAL STUDY ON 3-D FLUID FLOW WITHIN THE MOLTEN POOL DURING UNEQUAL DIAMETER TWIN ROLL STRIP CAST-ROLLING

In this paper three-dimensional flow field in the molten pool between unequal diameter twin rolls has been studied by BFC technology and SIMPLEC numerical method. From the computed flow pattern,the characteristic of molten steel flow has been discussed. The dynamics generated by the feeding flow and the motivation of counter-rotating twin rolls produces a recirculating flow field nearby the small roll due to the larger room and less resistant here and fluid flows along the roll surface tangential nearby large roll and extends to two side dams. There is faintly flow around the dams of molten pool

Progress in twin roll casting of magnesium alloys: A review

Twin roll casting was commercialized for a strip production from ferrous and non-ferrous alloys in the 1950 s;however,its application to magnesium has proven difficult and still creates major challenges.This report describes global efforts in expanding manufacturing capabilities of magnesium sheet through twin roll casting path,offering many benefits,including a reduction in number of processing steps and energy savings.In addition to hardware design,alloy transformation during processing,product microstructure and properties,examples of successful solutions along with present technology and knowledge limitations are discussed.A particular attention is paid to developments at Canmet MATERIALS,having the only in North America pilot scale twin roll casting facility,devoted to magnesium.Efforts are described that aim at design of new magnesium alloys,which could take advantage of unique processing conditions during twin roll casting and contribute to the overall progress in magnesium sheet manufacturing.

Recrystallization behavior of cold rolled Al-Zn-Mg-Cu fabricated by twin roll casting

The Al-Zn-Mg-Cu alloy strip can be successfully fabricated by twin roll casting. In order to determine the effect of thickness reduction and heat treatment temperature on the recrystallization behavior, the strips were rolled and subsequently heat treated under various conditions. As a result, a fine grained microstructure （average grain size -13 μm, average grain aspect ratio -1.7） and high mechanical properties （UTS ≥360 MPa, δ ≥20%） were obtained by cold rolling with thickness reduction of 60% and heat treatment at 500 ℃ for 1 h. Also, the effect of the microstructure on mechanical properties of the Al-Zn-Mg-Cu alloy strip was discussed. Consequently, the low cost and high strength Al-Zn-Mg-Cu alloy sheet can be fabricated by twin roll casting by proper thermo-mechanical processes.

Mathematical modeling of thermo-mechanical behavior of strip during twin roll casting of an AZ31 magnesium alloy

The effect of set-back distance on the thermo-mechanical behavior of the strip during twin roll casting(TRC)of an AZ31 magnesium alloy was modeled using finite element method(FEM).Model validation was done by comparing the predicted and measured exit strip surface temperature as well as the secondary dendrite arm spacing(SDAS)through the thickness of the sheet to those measured during experiments.Model results showed as the set-back distance increases,the strip exit temperature decreases and the solidification front moves toward the entry of the roll gap.The cast strip also experiences more plastic deformation and consequently,the normal stress on the strip surface and effective strain at the strip center-line increase.Moreover,higher separating forces were predicted for longer set-back distances.Model predictions showed that changing the set-back distance by varying the final thickness has a more significant effect on the temperature and stress-strain fields than altering the nozzle opening height.

Effect of Oscillation Parameters to Flow Field in the Pool during the Oscillating Twin-Roll Strip Casting Process

During the oscillating twin?roll strip casting process, the quality of final products is directly influenced by the flow field distribution of molten metal in the pool. The variation in the flow field is caused by oscillating roller benefits, for homogeneous distribution of strip impurity, and decreasing the grain size. Thus, the quality of the strip could be improved. A numerical model was developed using the multiphase flow technology, coupled with heat transfer, fluid flow, solidification, and oscillation. Furthermore, a transient algorithm was adopted for simulating the oscillating twin?roll strip casting process of AlSi9Cu3 and 3104 aluminum alloy. This paper focuses on the flow distribution in the pool, in comparison with the traditional vertical twin?roll strip casting process, while the amplitude or frequency is chang?ing with the definite value of casting velocity, roller diameter, nozzle angle, and the strip thickness. Consequently, the conclusions were experimentally validated by oscillating twin?roll 3104 aluminum alloy strip casting. Vibrating casting technology can change the flow field in the pool by vibration, which can improve the quality of the strip core.

3-D Numerical Simulation of the Electromagnetic Dam of Twin Roll Casting using Edge Element Method

The 3-dimension numerical simulation study on the electromagnetic dam used in the twin roll caster has been performed by using the edge element method. It was found that the materials and structures of the roll collars have great influence on the distribution of the magnetic flux density, eddy current density and the electromagnetic force in the molten pool. The conductive collars make the magnetic flux density decreased in the molten pool, but it also makes the magnetic force more uniformly, and the force in the low part of the molten pool where needs greater force have increased some what. The conductive collars make the EMD device more effective than the nonconductive collars.

High Speed Twin Roll Casting of Aluminum Alloy Strips

The twin roll caster for aluminum alloys has many a dv antages. For example, rapid solidification, low equipment cost, and low running cost, etc. However, the twin roll caster has some disadvantages. They are slow c asting speed and limitation of alloys. In the conventional twin roll caster, the casting speed is slower than 10 m/min. Aluminum alloys, which freezing range is wide, can not be cast. In the present study, break through of these problems wa s tried, and a new type twin roll caster was devised. A vertical type twin roll caster equipped with a nozzle was devised in order to cast aluminum strips at the speeds higher than 60 m/min. Characteristic features of this caster were vertical type, use of copper rolls, low separating force (n o operation of rolling), no use of lubricant, and equipment of the nozzle. In th e high speed roll casting, feed of molten metal of the vertical type twin roll c aster was easier than that of the conventional horizontal type caster. The use o f the copper rolls made cooling rate higher. The low separating force and the us e of the copper rolls prevented sticking of the strip to the roll. The lubricant was not needed, as the sticking of the strip to the roll did not occur. No use of the lubricant was useful to increase the cooling rate and casting speed of th e strip. The nozzle was used in order to improve contact condition (heat transfe r) between the melt and the rolls by hydrostatic pressure. In the twin roll cast er of the present study, many devices were done to improve the cooling condition of the strip in order to increase the casting speed. It was said that the roll casting of A5182 was very difficult, as freezing zone of A5182 was very wide. However, A5182 strip could be cast at high speeds up to 120 m/min using the twin roll caster of the present study. The microstructure of the strip cast using the conventional type twin roll caster is columnar structu re. The microstructure of the strip cast using the twin roll caster of the prese nt study was not columnar but equiaxed structure. It is said that mechanical pro perties of the strip cast using the twin roll caster is cheaper than that of the strip made from DC casting. However, the mechanical properties of the strip cas t using the twin roll caster in the present study were almost same as the proper ties of the strip made from DC casting. The thickness of the strip cast using th e twin roll caster of the present study was from 1.5 mm to 2.5 mm, and this thic kness was thinner than that of the strip cast using the conventional twin roll c aster. Semisolid roll casting was tried in order to increase the roll speed more and mo re. The twin roll caster of the present study was equipped with a cooling slope in order to make semisolid slurry. The cooling slope was the simplest process to make the semisolid slurry. Solid rate of the semisolid slurry was about 10%. Th e casting speed increased up to 180 m/min by the effect of semisolid casting. Me chanical properties were improved by the semisolid casting, too.

Numerical Simulation of Two Types of Electromagnetic Edge Dam Used in Twin Roll Strip Casting

Two types of electromagnetic edge dams were analyzed by using finite element method in present paper. The magnetic vector potential method and edge element method were used. The distributions of the magnetic field, the eddy current intensity and the magnetic force were obtained from the computing. The differences in these fields were explained according to the two types of electromagnetic dam, and characters of their application in twin roll casting were also discussed.

Influence of Feeding Mode on Flow and Temperature Field for Twin Roll Strip Casting Process

A three-dimensional finite element method was developed to simulate the fluid flow,heat transfer and solidification for twin roll strip casting.An improved two-equationκ-εmodel was used to incorporate the turbulence in fluid flow.The influence of vertical feeding and submerged entry nozzle feeding on the flow and temperature field was discussed.The optimum submersion depth and entry angle of submerged nozzle were obtained through comparison of the simulation results.

Microstructure and Eutectic Carbide Morphology of the High Speed Steel Strips Produced by Twin Roll Strip Casting Process

The M2 high-speed steel strip was produced by using the laboratory scale twin roll strip caster. The microstructure and eutectic carbide morphology of thus produced products were observed and analyzed, and the comparison of those with conventional products was carried out. The effects of the processing parameters such as the melting temperature, the pouring temperature, rolling speed and separating force on the microstructure and eutectic carbide morphology and their distribution were analyzed. The spheroidizing process of the strips in the annealing process was investigated. The relations between the growth and spheroidizing of the eutectic carbide and the annealing technology were obtained, and the mechanism of the twin roll strip casting process improving the eutectic carbide spheroidizing was discussed. The theoretical instruction for determining the subsequent treatment process was provided.

Recrystallization behavior of twin roll cast low carbon steel strip

The dynamic and static recrystallization behaviors of twin roll cast low carbon steel strip were investigated with an attempt to provide guiding deformation parameters for the on line hot rolling.In order to investigate dynamic recrystallization behavior,as cast strip was reheated and soaked with austenite grain size similar to the width level of the as cast columnar structure.Tensile test was used and the deformation temperature is in the range of 900℃to 1 100℃and strain rates are 0.01 s^(-1),0.1 s^(-1),1 s^(-1).The activation energy and stress exponent were determined as 306kJ/mol and 4.69 respectively.The ratio of critical strain to the peak strain is 0.65,and that of critical stress to the peak stress is 0.92.The dependence of the peak strain on the initial grain size and Zener - Hollomon parameters Z isε_p =9.1×10^(-4)×D_0^(0.48)Z^(0.13).The kinetics of the dynamic recrystallization and recrystallized grain size was predicted using models published.The as cast coarse austenite were dramatically refined after complete dynamic recrystallization.For static recrystallization,the tensile test was carried out on Gleeble -3500 thermo - mechanical simulator.The deformation temperature is in the range of 800℃to 1 200℃with strain rate 0.01 s^(-1) to 1s^(-1).The pre strain is fixed at 0.04 to 0.12 and the inter-hit delay time varies from 1 s to 3 000 s.The activation energy and Avrami exponent of static recrystallization were determined as 241 kJ/mol and 0.54 respectively.A kinetics model was proposed to describe the static recrystallization kinetics.The predicted results were in good agreement with the experimental results.

Fluid Resonance Between Twin Floating Barges with Roll Motion Under Wave Action

The wave-induced fluid resonance between twin side-by-side rectangular barges coupled with the roll motion of the twin barges is investigated by both numerical simulation and physical model test.A 2D numerical wave flume,based on an open source computational fluid dynamics(CFD)package OpenFOAM,is applied for the numerical simulation.After numerical validations and convergent verifications,the characteristics of the fluid resonance in the gap between the twin rolling side-by-side barges are examined.The resonant frequency of the oscillating fluid in the gap between the twin rolling barges decreases compared with that between the twin fixed barges.Generally,the twin barges roll in the opposite directions,and their equilibrium positions lean oppositely with respect to the initial vertical direction.A physical model test is carried out for a further investigation,in which the twin barges are set oppositely leaning and fixed.From the present experimental results,a linear decrease of the resonant frequency with the increasing leaning angle is found.Combined with the numerical results,the deflection of the equilibrium positions of the twin barges is a relevant factor for the resonant frequency.Besides,the effects of the gap width and incident wave height on the fluid resonance coupled with roll motion are examined.

Deformation Behavior and Microstructure Evolution of Wrought Magnesium Alloys

There are many researches on the deformation behavior of wrought magnesium alloys, such as AZ31, AZ80, AZ91, and ZK60 magnesium alloys at different temperatures and strain rates, but few of them focuses on the deformation behavior of AZ41M and ZK60M alloys, especially under the twin-roll casting (TRC) state. Meanwhile, the existing researches only focus on the grain refinement law of the magnesium alloys under deformation conditions, the deformation mechanism has not been revealed yet. The hot compression behavior of AZ41M and ZK60M magnesium alloys under the temperature and strain rate ranges of 250-400 ℃ and 0.001-1 s-1 are studied by thermal simulation methods using Gleeble 1500 machine and virtual simulation using finite element analysis software. Simulation results show that sine hyperbolic law is the most suitable flow stress model for wider deformation conditions. The most reasonable selected deformation conditions of ZK60M alloy is 350 oC/0.1 s-1 for TRC and 350 oC/1 s-1 for conventional casting (CC), while AZ41M alloy is 300 oC/0.01 s-1 for TRC and 350 oC/0.1 s-1 for CC. Deformation behavior and dynamic recrystallization (DRX) mechanism of them are analyzed at the same deformation conditions. The microstructures of AZ41M and ZK60M alloys are observed at different deformed conditions by optical microscopy (OM) and electron back scatter diffraction (EBSD) and it reveals the flow behavior and deformation mechanism of them. Working harden and work soften contribute to the activation of basal, non-basal slip systems which promote DRX. The proposed research reveals the deformation behavior and mechanism of the AZ41M and ZK 60M magnesium alloys and concludes their optimized deformation parameters and processes and provides a theory basis for their manufacturing and application.

Delayed Fracture Behavior of CrMo Type High Strength Steel Containing Vanadium

The netlike eutectic carbide in twin roll casting strip of W9Cr4V2 was dissolved and broken up gradually with increasing heating temperature during annealing treatment. Almost all eutectic carbides exist in granular form with heating temperature up to 950 ℃. It is considered that the refining of lamellar spacing made it possible for eutectic carbide to be granulated.

Effect of Pre-cold Rolling-Induced Twins and Subsequent Precipitated x-Phase on Mechanical Properties in a β-Type Ti–Mo Alloy

This paper reported an effectiveness of pre-cold rolling-induced{332}／113[twins combined with subsequent isothermal x-phase formation for enhancement of uniform elongation in a b-type Ti–15Mo alloy with high yield strength level.Mechanical{332}／113[twins were induced by cold rolling with an thickness reduction of 5%,which had little effect on x-phase precipitation after aging at 573 K for 3.6 ks.Twinning after the cold rolling was further activated during tensile deformation,even with the presence of isothermal x-phase.This combination of twins and x-phase enhanced uniform elongation from 0 to 9%at yield strength level of 890 MPa.The high yield strength was mainly dominated by dislocation slip due to the isothermal x-phase formation,and early onset of plastic instability after yielding was hindered due to the pre-cold rolling-induced twins.Dynamic microstructural refinement was induced by further twinning activation during deformation,which resulted in high work hardening rate corresponding enhancement of uniform elongation.

Electrochemical Method to Accelerate Metal-Slag Reaction

According to the principle of similarity theory, a water model of twin roll strip caster was built. The level fluctuation was measured with an ultrasonic level detector. The effect of nozzle design, casting rate, pool depth and nozzles immersion depths on the level fluctuation was studied. And a level fluctuation mathematical model was developed. The experimental results provided a basis to further optimize the nozzle design and technological parameters of twin roll strip caster.

TiAl ALLOYS FOR INDUSTRIAL USE

Gamma titanium aluminide (γ-TiAl)intermetallic compounds are spotlighted as lightweight heat-resistant materials, and have been investigated extensively to aiming commercial use.Fundamental approaches in which phase diagrams of Ti -Al -Cr and TiAl -Nb have been studied based on the experimental data and calculations , have been performed in the national project For industrial approach, ingot process and direct casting process have been developed to provide sheet form of TiAl. By these approaches, γ-TiAl base ,intermetallic compounds show a great possibility to apply in the variety of fields .However, a more detailed understanding of phase equilibrium in Ti-Al -X and the relationship between the mechanical properties and microstructure will be necessary

Twinning Behavior of a Basal Textured Commercially Pure Titanium Alloy TA2 at Ambient and Cryogenic Temperatures

Twinning greatly affects the microstructure and mechanical performance of titanium alloys.The twinning behavior of a basal textured commercially pure titanium TA2 plates rolled to 4% reduction at the ambient and cryogenic temperatures has been investigated.Microstructures of the rolled samples were investigated by optical microscope（OM）and the twinning analysis was carried out based on orientation data collected by electron back-scatter diffraction（EBSD）.{1122}contraction twins,{1124}contraction twins and {1012}extension twins have been observed.Twinning mode activity varied with rolling temperature.Twinning is considered as the dominant deformation mechanism during rolling at both temperatures for the strain condition.Larger proportion of grains activates twinning during cryorolling,and greater number and more diverse types of twins are observed;manifestly related to the suppression of dislocation slips at the cryogenic temperature.{1122}contraction twins are the dominate twin type within samples rolled at both temperatures.Several{1124}contraction twins are observed in the cryorolled sample while there are only a few in the sample rolled at room temperature.A few tiny{1012}twins have been identified in both samples.{1124}contraction twins are preferentially activated at cryogenic deformation temperature and the{1012}extension twins may result in local strain accommodation.