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.

FEM Analysis of Physical Field in Level Rolling Process of Inversion Casting by ANSYS Program

The strain physical field in level rolling process of inversion casting was analyzed by ANSYS program.Plastic strain,stress and displacement were gained.The results show that only surface strain takes place) the maximum stress exists in the geometrical deformation zone;In the deformation transition zone and the part leaving the rollers,different stress exists.The rolling force estimated with ANSYS program corresponds to those measured.

EFFECTS OF ELECTROMAGNETIC FIELD ON CASTING-ROLLING STRIP BREAKDOWNS

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Influence of roll speed difference on microstructure, texture and mechanical properties of 7075 aluminum plates produced via combined continuous casting and rolling process

The influences of the dissimilarity in the roll speeds on the microstructure, texture and mechanical properties of 7075 aluminum plates produced via combined continuous casting and rolling(CCCR) process were investigated. Several experiments were conducted with three different upper/lower roll rotational speed ratios(ω/ω0, ω is the upper roll rotational speed and ω0 is the lower roll rotational speed), namely 1:1, 1:1.2 and 1:1.4. It was found that the greatest dissimilarity in the roll speed(ω/ω0=1:1.4) improved the yield strength and ultimate tensile strength of 7075 Al plate in the rolling direction by 41.5% and 21.9%, respectively. Moreover, at a roll speed ratio of ω/ω0=1:1.4, the average grain size was decreased by 36% whereas the mean hardness of the transverse cross-section of the finally rolled plate was increased by about 9.2%. Texture studies also revealed that the more the difference in the roll speeds was, the greater the isotropy and the hardness of the final product were. Nevertheless, conducting CCCR operation with different roll speeds resulted in about 6% reduction in the elongation of the deformed plate.

Microstructural evolution and enhanced mechanical properties of Mg?Gd?Y?Zn?Zr alloy via centrifugal casting, ring-rolling and aging

A ring-shaped Mg?8.5 Gd?4 Y?1 Zn?0.4 Zr(wt%) alloy was manufactured via centrifugal casting and ring-rolling process. The effects of accumulative ring-rolling reduction amount on the microstructure, texture, and tensile properties of the alloy were investigated. The results indicate that the microstructure of centrifugal cast alloy consists of equiaxed grains and network-like eutectic structure present at grain boundaries. The ring-rolled alloy exhibits a characteristic bimodal microstructure composed of fine dynamic recrystallized(DRXed) grains with weak basal texture and coarse un-DRXed grains with strong basal texture, along with the presence of LPSO phase. With increasing amount of accumulative ring-rolling reduction, the coarse un-DRXed grains are refined via the formation of increasing amount of fine DRXed grains. Meanwhile, the dynamic precipitation of Mg5 RE phase occurs, generating a dispersion strengthening effect. A superior combination of strength and ductility is achieved in the ring-rolled alloy after an accumulative rolling reduction of 80%. The tensile strength of this ring-rolled alloy after peak aging is further enhanced, reaching 511 MPa, while keeping a reasonable ductility. The salient strengthening mechanisms identified include the grain boundary strengthening of fine DRXed grains, dispersion strengthening of dynamic precipitated Mg;RE phase, short fiber strengthening of LPSO lamellae/rods, and precipitation strengthening of nano-sized prismatic β precipitates and basal γ precipitates.

Microstructure evolution and mechanical properties of Cu-0.36Be-0.46Co alloy fabricated by heating-cooling combined mold horizontal continuous casting during cold rolling

Cu-0.36 wt.%Be-0.46 wt.%Co alloy plate with 300 mm in width and 10 mm in thickness prepared by heating-cooling combined mold(HCCM) horizontal continuous casting was cold rolled. Microstructure evolution and mechanical properties of the alloy as well as its deformation mechanism were investigated. The results showed that the as-cast alloy plate had columnar grains along the length direction, good surface quality and elongation of 35%, which was directly large-reduction cold rolled without surface treatment, and the accumulative cold rolling reduction reached 98%. When the reduction was small(20%), numerous dislocations and dislocation cells formed, and the deformation mechanism was dislocation slip. When the reduction was 40%, deformation twins appeared, and interactions between twins and dislocation cells induced strip-like dislocation cells. When the reduction exceeded 60%, shear bands formed and apparent crystal rotation in the micro-region happened. Further increasing the reduction, the amount of the shear bands rose and they interacted with each other, which refined the grains apparently. The tensile strength and hardness increased from 353 MPa and HV 119 of the as-cast alloy to 625 MPa and HV 208 with 95% reduction, respectively, and the elongation reduced from 35% to 7.6%. A process of HCCM horizontal continuous casting-cold rolling can work as a novel compact method to fabricate Cu-Be alloy sheet.

DANIELI concepts and experiences in thin slab casting and rolling technology for HRC production—the evolution of a winning process route to face increasing market requirements

The direct rolling process for hot strip production,where the thin slab caster is connected directly to the mill,has gained market share rapidly because of its remarkable advantages in terms of energy savings and investment cost over the conventional hot strip mills. However,the unquestionable advantages of the first-generation applications of this plant concept also entail significant limitations both in productivity and steel grades that can be produced. Since his first pioneering applications,Danieli considered strategic the development of new technical solutions specifically conceived to overcome these limitations with the goal of increasing plant production volumes and enlarging steel grade product mix,in order to cover the gap between "Conventional mill" and "Thin slab casting and rolling" process routes. In order to reach this goal,Danieli has developed a complete portfolio of plant lay outs adopting Thin Slab Casting and Rolling technologies,each of them conceived to guarantee the optimal CAPEX and OPEX parameters in fitting with market requirements our Customer intend to target.in terms of productivity,steel grades and coil dimension product mix. Danieli TSR(Thin Slab Rolling) fTSR(flexible Thins Slab Rolling) QSP(Quality Strip Production) and ETR(Extra Thin Rolling) plant configurations are analyzed in this paper. With this diversified approach,Danieli solutions are most appropriate answers to thin slab casting and rolling to produce hot rolled coils with superior quality and an extremely diversified range of steel grades. Already,this approach has allowed Danieli plants to:①exceed the threshold production of 3.0 Mt/a with 2 casting strands in operation as done in Tangshan Iron and Steel plant in P.R.China since 2005;②expand the product mix to include virtually all the steel grades used for flat product applications,including the most demanding ones,such as peritectic(in Essar Algoma Canada and Benxi Iron and Steel,China),micro-alloyed,and silicon steels,for the most sophisticated applications,such as automotive and pipe manufacturing,including Arctic applications,(as done in OMK plant in Russia);③extend the range of final strip thicknesses to include ultra thin gauges,down to 0.8 mm(as in Ezz Flat Steel,in Egypt).

Creep Behaviors of DA Casting and Rolling GH4169 Superalloy

After the billet of Casting and Rolling GH4169 alloy was directly aged (DA) treated at 720 ℃ and 620 ℃, creep behavior and deformed features of the alloy were investigated by means of the measurement of creep curves and microstructure observation. Results show that the DA Casting and Rolling GH4169 Superalloy displays a lower strain rate during creep and longer lifetimes under the condition of the applied stress of 700 MPa at 650 ℃ , the creep lifetimes of the alloy decrease to 127 h as temperature is elevated to 660 ℃ , and therefore the alloy exhibits an obvious sensitivity of the applied temperatures. During creep, the deformation mechanism of the alloy is thought to be the twinning deformation and slipping of dislocation within the twinning regions. Thereinto, the dislocation slipping of the single and double orientations occur within the twins. As creep enters the tertiary steady state stage, the micro-crack appears on the grains boundaries along the direction vertical to the applied stress axis, and expands along the grain boundary up to fracture.

New Technique of Casting-rolling Strips for Semi-solid Magnesium Alloys

The conjugation of semi-solid process technique and casting-rolling technique applied to produce the magnesium strips was studied. The semi-solid slurry has been prepared continuously by the mechanical method and its temperature was controlled strictly at the same time. AZ91D and AZ31 casting magnesium alloys were applied to the experiment. The casting-rolling strips with non-dendritic structure were obtained and its main mechanical property is better. The process ability of the casting-rolling strips was studied. It is significative to link the semi-solid process techniques and casting-rolling techniques, through which we can get high quality magnesium alloy strips with non-dendritic structure and improve the overall properties of the products.

Mechanism and simulation of external cooling in aluminum casting-rolling process

External cooling technology is one of the key technologies to realize fast-casting-rolling process of aluminum, i.e. using compulsive cooling on the external surface of rollers and aluminum plate to improve the cooling ability of system, increase casting-rolling speed, and enhance the quality of aluminum plate. Heat transfer model of casting-rolling process was proposed and the characteristics of the temperature field of roller-plate system were analyzed. The influences of external cooling surface of the plate and the roller on the temperature field of the roller and the aluminum plate and the casting-rolling speed were discussed, and the relationship between external cooling and internal cooling were also analyzed. Experiment results show that, with the increase of casting-rolling speed, the influence of cooling plate surface on increasing casting-rolling speed was gradually decreased, but that of cooling roller surface was enhanced. Different mechanisms of external cooling plate surface and roller surface for improving casting-rolling speed account for this phenomenon.

Effect of Substrate Movement Speed by Synchronous Rolling-casting Freeform Manufacturing for Metal on Microstructure and Mechanical Property of ZLl04 Aluminum Alloy Slurry

Synchronous rolling-casting freeform manufacturing for Metal(SRCFMM) means that the refined liquid metal is continuously pressed out from the bottom of crucible. There is a horizontal movable plate beneath the outlet. The clearance between the outlet and the plate is about several hundred micrometers. SRCFMM, similar to additive manufacturing, implies layer by layer shaping and consolidation of feedstock to arbitrary configurations, normally using a computer controlled movable plate. The primary dendritic crystal is easily crushed by movement of substrate in the rolling-casting area. ZL104 was used as the test materials, determining the control temperature by differential scanning thermal analysis(DSC), preparing a kind of samples by SR CFMM, then analyzing microstructures and mechanical property of the samples. Characteristics and distribution of the primary particles were assessed by optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectrum(EDS) and image analysis software. Mechanical property of the samples was assessed by vickers hardness. The results show that the samples fabricated by SRCFMM have uniform structures and good performances with the velocity of the substrate controlled about 10 cm/s and temperature at about 580 ℃.

THE ESTABLISHMENT OF CALCULATION FORMULA FOR CASTING－ROLLING FORCE OF VISCOUS FLUID AND THE INFLUENCE OF TECHNOLOGICAL FACTORS

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Establishment of mathematical moment model in twin casting rolling rolls

In continuous casting rolling process, the deformed body is different from the hot rolling strip. The metal in casting rolling zone is first assumed to be viscous fluid and the mathematical model of casting rolling force is established, then the calculating formula for casting rolling torque is derived. In addition, considering the effects of deforming cone and appendant torque of rotary junctions sealing ring, the calculating model which accords with casting rolling condition is found out. Theoretical formula is proved by experiment.

Slab Storage Calculation Method for Continuous Casting-Hot Rolling

Based on load-oriented manufacturing control theory,different combining modes and slab storage calculation method for continuous casting and hot rolling were discussed.The buffer capacity index of continuous casting-rolling was introduced,and the reasonable slab storage under different combining modes was calculated with buffer capacity index of 120.00 hfor CCR,79.20 hfor HCR,19.68 hfor DHCR and 3.84 hfor DR.Thin slab is 1.20 h,and the strip is zero.Theory gist was provided for steel enterprise to decrease storage.

The future of the twin-roll strip casting and rolling process

Twin-roll strip casting and rolling is a typical near-net-shape steel manufacturing process.The twin-roll strip casting and rolling of low-carbon steel strips has made a number of breakthroughs and achieved significant results during the past 20 years.Baosteel has been paying close attention to the development of this technology and set up a research and development project focused on its industrialization in 2001.The Ningbosteel-Baosteel strip casting industrialization demo project(NBS),which was launched in 2016,marks the strip-casting technology(registered as Baostrip) developed by Baosteel as having reached an advanced international level after 15 years of effort.This paper summarizes the results obtained in the industrialized demonstration plant and considers the future development of strip casting and rolling.

Grain refinement of Mg-Al alloys by optimization of process parameters based on three-dimensional finite element modeling of roll casting

To study the influence of roll casting process parameters on temperature and thermal-stress fields for the AZ31 magnesium alloy sheets,three-dimensional geometric and 3D finite element models for roll casting were established based on the symmetry of roll casting by ANSYS software.Meshing method and smart-sizing algorithm were used to divide finite element mesh in ANSYS software.A series of researches on the temperature and stress distributions during solidification process with different process parameters were done by 3D finite element method.The temperatures of both the liquid-solid two-phase zone and liquid phase zone were elevated with increasing pouring temperature.With the heat transfer coefficient increasing,the two-phase region for liquid-solid becomes smaller.With the pouring temperature increasing and the increase of casting speed,the length of two-phase zone rises.The optimized of process parameters（casting speed 2 m/min,pouring temperature 640 ℃ and heat transfer coefficient 15 kW/（m2·℃） with the water pouring at roller exit was used to produce magnesium alloy AZ31 sheet,and equiaxed grains with the average grain size of 50 μm were achieved after roll casting.The simulation results give better understanding of the temperature variation in phase transformation zone and the formation mechanism of hot cracks in plates during roll casting and help to design the optimized process parameters of roll casting for Mg alloy.

Numerical simulation of the temperature fields of stainless steel with different roller parameters during twin-roll strip casting

The temperature field of stainless steel during twin-roll strip casting was simulated by experiment and a finite element （FE） model. By comparing the measured result with the simulated values, it is found that they fit close to each other, which indicates this FE model is effective. Based on this model, the effects of roll gap （t） and roll radius （R） on solidification were simulated. The simulated results give the relationship between t or R and the position of the freezing point. The larger the t is and the smaller the R is, the closer the position of the freezing point is to the exit.

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.

Effects of ultrasonic treatment on structure of roll casting aluminum strip

The experiment of ultrasonic treatment of roll casting aluminum strip on plane twin-roll cast-roller with double-heads ultrasonic tools was carried out, and the metallographic structure of the roll casting aluminum strip treated by ultrasonic was studied. The results show that ultrasonic treatment can refine the grain of the roll casting aluminum strips and make the structure of the strips more homogeneous. The effect is the best when the power of ultrasonic is 300 W and the incident angle of the guide rod is 45、. The mechanism of acoustic cavitations and acoustic flow on grain refinement was also discussed. The heat effect of intensity ultrasonic was studied. The present problems during ultrasonic roll casting process, such as the imperfect cooling system, the inaccurate calculation of ultrasonic energy, and the shape and position of the guide rod to be improved were pointed out.

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.