Mechanism of plasticity enhancement of AZ31B magnesium alloy sheet by accumulative alternating back extrusion

Accumulative alternating back extrusion was a potential fine-grain modification method.In this paper,it was an innovative attempt to develop high-performance magnesium alloy sheet by this process.Under the condition of 350 K,commercial AZ31 magnesium alloy was made into billet by accumulative alternating back extrusion,and then extruded into fine-grain magnesium alloy sheet.Through a systematic study of its microstructure and mechanical properties,the results showed that the initial state had an important influence on the evolution of the structure during extrusion.After accumulative alternating back extrusion to produce the billet,the grain size of the sheet obtained by extrusion was significantly refined,which was related to the accumulation of deformation and grain refinement during the alternating loading process.Grain refinement caused the proportion of dynamic recrystallization inside the sheet with 2 cycles of accumulative alternating back extrusion to drop to 27%.With the increase of extrusion cycles from 2 to 4,the high density of dislocations led to an increase in the proportion of dynamic recrystallization and finer grains.The texture changed from strong basal texture to weak bimodal texture.The results of uniaxial tensile test show that due to grain refinement and texture change,the yield strength was significantly reduced,and the plasticity was significantly improved.It was verified that accumulative alternating back extrusion was meaningful for subsequent processing,and it also provided scientific guidance for the development of fine-grained magnesium alloy sheet.

Unveiling the planar deformation mechanisms for improved formability in pre-twinned AZ31 Mg alloy sheet at warm temperature

To investigate the role of pre-twins in Mg alloy sheets during warm planar deformation, the stretch forming is conducted at 200 ℃. Results suggest the formability of the pre-twinned AZ31 Mg alloy sheet is enhanced to 11.30 mm. The mechanisms for the improved formability and the deformation behaviors during the planar stretch forming are systematically investigated based on the planar stress states. The Schmid factor for deformation mechanisms are calculated, the results reveal that planar stress states extremely affect the Schmid factor for {10-12}twinning. The detwinning is activated and the prismatic slip is enhanced in the pre-twinned sheet, especially under the planar extension stress state in the outer region. Consequently, the thickness-direction strain is accommodated better. The dynamic recrystallization(DRX) type is continuous DRX(CDRX) regardless of the planar stress state. However, the CDRX degree is greater under the planar extension stress state.Some twin lattices deviate from the perfect {10-12} twinning relation due to the planar compression stress state and the CDRX. The basal texture is weakened when the planar stress state tends to change the texture components.

Textural Evolution of AZ31B Magnesium Alloy Sheets Undergoing Repeated Unidirectional Bending at Room Temperature

In this paper, repeated unidirectional bending （RUB）, was applied to improve the texture of AZ31B magnesium alloy sheets so as to enhance their stamping properties. The samples undergoing RUB were annealed at different temperatures. The mechanical properties, formability, textural components and microstructure of the samples before and after RUB were characterized and compared. It was found that the basal textural component was reduced dramatically by RUB, and that （1212） and （1211） textural components appeared. Annealing has a great effect on the mechanical properties of samples undergoing RUB. The plasticity and stamping formability of samples were greatly improved by RUB and annealing at 260℃ for 1 h, and elongation to fracture and Erichsen value were increased to 38% and 67%, respectively.

Refining Effect of a New Al3Ti1B1RE Master Alloy on Al Sheets Used for Can Manufacture and Behavior of Rare Earths in Master Alloy

The refining effect of Al3Ti1B1RE master alloy on Al sheets used for pressure can manufacture and the behavior of mixed rare earths in master alloy were investigated with XRD, OM, SEM and EDAX. It is found that the refining effect of the refiner on the material has superiority over foreign or domestic Al5Ti1B refiner, and the refiner still retains its refining ability for 6 h after adding it to molten Al, thus improving the strength and plasticity of the material remarkably. The excellent refining effect and stability of AlTiBRE refiner result from that RE can lower the surface energy of molten Al and improve the wetting characteristics of molten Al on refinement nuclei such as TiAl 3, TiB 2, etc., thus giving full play to the effect of heterogeneous nucleation and impeding the congregating tendency of TiB 2 phase in molten Al. At the same time, RE gathering in front of solid/liquid interface are also easy to cause composition supercooling in molten Al, thus impeding the growth of α Al grains and promoting α Al nucleation on refinement nuclei. In addition, RE also play certain role in purification and grain refinement, or modification, especially their effect of purification can improve the metallurgical quality of AlTiBRE master alloy.

Characterization of W80Cu20 alloy sheet prepared by hot-rolling

Multi-pass hot-rolling technique was used to fabricate W80Cu20 alloy,and its properties were characterized in this paper.Results show that the W-Cu alloy sheets with a thickness of 0.5 mm and a relative density of99.87%can be successfully made using this new technique at 800℃.In hot-rolling process,Cu phases are closely surrounded by W particles under the rolling stress to form a network microstructure,thus making significant increase in electrical and thermal conductivity up to53.00%and 24.44%,respectively.Transverse and longitudinal hardness of the W–Cu sheets significantly increase due to the enhanced densification and deformation strength.Similar to that of the raw materials,three fracture types were observed in the hot-rolled materials,i.e.,ductile fracture of Cu binding phases,trans-granular fracture of W phases,and W–W interfacial fracture.

Enhanced mechanical properties of Mg-3Al-1Zn alloy sheets through slope extrusion

A novel extrusion approach,entitled slope extrusion(SE),was employed to manufacture AZ31(Mg-3Al-1 Zn,wt%)alloy sheets.The microstructures,textures,and mechanical properties were investigated,compared with those of the AZ31 sheet fabricated by conventional extrusion(CE).Through the combination of finite element simulation and actual experiment,the ultimate results indicated that significant grain refinement(from 9.1 to 7.7 and 5.6μm)and strong basal texture(from 12.6 to 17.6 and 19.5 mrd)were achieved by the SE process.The essence was associated with the additional introduced inclined interface in the process of SE,which could bring about more asymmetric deformation and stronger accumulated strain along the ND when compared with the process of CE.As a consequence,the SE sheets exhibited a higher yield strength(YS)and ultimate tensile strength(UTS)than the counterparts of the CE sheet,which was mainly assigned to the synergistic effects from grain refining and texture strengthening.

The Stamping Formability of AZ31 Magnesium Alloy Sheet Improved by Equal-channel Angular Pressing

Equal channel angular pressing （ECAP） processing and annealing were applied to the AZ31 magnesium alloy sheets to evaluate the potential improvement in the mechanical properties and formability. The ECAP experiment was conducted at 300 ℃ in a die having an included angle of 90o between two channels by the BCZ route with the sheets rotated by 90°about the normal axis of plate plane. The tensile tests and conical cup tests were conducted at various temperatures from 20 to 250 ℃. The experimental results indicated that improving the working temperatures could lead to the soft in the material and the enhancement of ductility. Comparatively, the ECAPed AZ31 alloy sheets showed the lower yield strength and smaller conical cup value （CCV） than the unECAPed counterpart in the room temperature. The difference in yield strength between them became small in the elevated temperature, but the ECAPed samples still had the smaller CCV value, implying the improved formability. The texture of the AZ31 alloy sheets could be modified by ECAP and the decrease in the yield strength and more uniform deformation realized in the material, so the formability of AZ31 alloy sheets was improved.

Strain-hardening and warm deformation behaviors of extruded Mg-Sn-Yb alloy sheet

Strain-hardening and warm deformation behaviors of extruded Mg-2Sn-0.5Yb alloy(at.%)sheet were investigated in uniaxial tensile test at temperatures of 25-250 ℃ and strain rates of 1×10^(−3) s^(−1)-0.1 s^(−1).The data fit with the Kocks-Mecking type plots were used to show different stages of strain hardening.Besides III-stage and IV-stage,the absence of the II-stage strain hardening at room temperature should be related to the sufficient dynamic recrystallization during extrusion.The decrease of strain hardening ability of the alloy after yielding was attributed to the reduction of dislocation density with increasing testing temperature.Strain rate sensitivity(SRS)was significantly enhanced with increasing temperature,and the corresponding m-value was calculated as 0.07-0.12,which indicated that the deformation mechanism was dominated by the climb-controlled dislocation creep at 200 ℃.Furthermore,the grain boundary sliding(GBS)was activated at 250 ℃,which contributed to the higher SRS.The activation energy was calculated as 213.67 kJ mol^(−1),which was higher than that of lattice diffusion or grain boundary self-diffusion.In addition,the alloy exhibited a quasi superplasticity at 250 ℃ with a strain rate of 1×10^(−3) s^(−1),which was mainly related to the fine microstructure and the presence of the Mg2Sn and Mg2(Sn,Yb)particles.

Effect of high density electropulsing treatment on formability of TC4 titanium alloy sheet

An annealed TC4 titanium alloy sheet was treated by high density electropulsing(Jmax=(5.09-5.26)×103A/mm2,tp=110μs)under ambient conditions.The effect of electropulsing treatment(EPT)on the plastic deformation behavior of TC4 titanium alloysheet was studied using uniaxial tension tests.The experimental results indicate that electropulsing treatment significantly changesthe mechanical properties of sheet metal:the uniform elongation is increased by 35%,the yield stress is decreased by 19.8%and theyield to tensile ratio is decreased by 17.6%.It is of significant meaning to improve the formability of TC4 titanium alloy sheet.Theoptical microscope and scanning electron microscope(SEM)were used to examine the changes of the microstructure and the fracturemorphology before and after the electropulsing treatment.It is found that recrystallization occurs in the sheet metal and dimples infracture surface are large and deep after the electropulsing treatment.The research results show that the electropulsing treatment is aneffective method to improve the formability of titanium alloy sheets.

Microstructures and tensile properties of AZ31 magnesium alloy thin sheet

Microstructures, tensile properties, fracture characteristics of commercial AZ31 magnesium alloy thin sheet were studied by optical microscopy, scanning electron microscopy and uniaxial tensile test. Tensile tests were carried out at room temperature and 473K, with strain rates of 8.3×10 -44.2×10 -3s -1. The results show that grain refinement effects are better at high temperature, and it increases with the decrease of strain rate at 473K. Compared with that tested at room temperature, no apparent uniform plastic deformation stage exists in the stress—strain curves tested at 473K; afterwards, the stress—strain curve presents wavelike downward under condition of the small strain rate. Yield strength and tensile strength of the alloy decrease drastically while the elongation increases greatly. With the increase of strain rate, yield strength and tensile strength of the alloy increase, but the elongation decreases. The fracture of the alloy tested at room temperature is quasi-cleavage failure and ductile failure at 473K.

Research on the lack of alloying in the galvannealed coating of automotive sheet steel

Samples of the cross section microstructures of galvannealed steel sheets that lack alloying were analyzed. X-ray diffraction （XRD） tests were carried out. The study discovers that the deficit of alloying was higher on both sides of the steel sheet when compared to the center and the thickness of the coating on the sides was also higher than the center. The results of the XRD tests demonstrate that the microstructure of the coating with a lack of alloy is mainly composed of zinc,ζ and δ. They also indicate that the lack of alloying is mainly due to a lower galvannealing temperature and thicker coating. It is shown by the optical micrographs of coating that the δ phase forms first in a discontinuous manner at the interface and then rapidly pushes towards the coating and enlarges.

NICKEL-BASE ALLOY SHEET ALLOYS USED IN AEROSPACE APPLICATIONS

Many gas turbine components are made from nickel alloy sheet. Most are used for directing or containing gases at high temperatures and pressures where metal temperatures can be as high as 1090℃ (2000°F). These applications included combustor systems, casings and liners, transition and exhaust ducting, afterburners, and thrust reversere. Light weight components and sub-assemblies call for alloy sheet with high levels of stength and oxidation resistance. Complex component design calls for excellent ductility and ease of fabrication.The wide range of nickel alloy sheet alloys presently used in aircraft and land-based gas turbines is briefly described and typical properties presented. New sheet alloy developments, involving INCONEL￣* alloys 625LCF, 718SPF and MA754, are presented including the process routes involved and material properties.

Optimisation of alloy composition for highly-formable magnesium sheet

The effectiveness of Ca or Gd addition on ductility and formability of Mg-Zn-Zr based dilute alloys in deep drawing has not been systematically compared previously.In this study,formable Mg-Zn-Gd-Zr and Mg-Zn-Ca-Zr sheet alloys are produced by hot rolling.These sheets have similarly weakened basal texture,but the sheet of the Mg-Zn-Gd-Zr alloys has higher ductility and formability than that of Mg-Zn-Ca-Zr alloys.The combined addition of 0.2wt%Ca and 0.4wt%Gd to the Mg-1Zn-0.5Zr(wt%)alloy leads to a Mg-1Zn-0.4Gd-0.2Ca-0.5Zr alloy that has even better ductility,and its formability during deep drawing is comparable to the benchmark Al6016 sheet.An increase in Ca content from 0.2wt%to 0.5wt%leads to decreased sheet ductility and formability,predominantly due to grain boundary embrittlement.

Structure and properties of AZ31B magnesium alloy sheets processed by repeatedly unidirectional bending at different temperatures

Repeatedly unidirectional bending(RUB) was applied to the magnesium alloy sheet to improve the basal texture.The effect of RUB temperature on resulting structure and room temperature properties was investigated.The texture components of the sheet undergoing RUB at recovery temperature were similar to those of the sheet undergoing RUB at room temperature(RT).As the RUB temperature increased to above recrystallization temperature,the texture components became more disperse and the pyramidal components increased.With the increase of RUB temperature,the grain size near the surface of the sheets undergoing RUB tended to grow up.When the sheets were processed by RUB at medium-high temperature followed by annealing at 533 K,the yield strength and fracture elongation were lower than those of the cold rolled sheet;however,the Erichsen value was slightly higher than that of the cold rolled sheet.The sheet undergoing RUB at RT followed by annealing at 533 K represented the best mechanical properties.

Application of new VBHF optimization strategy to improve formability of automobile panels with aluminum alloy sheet

A VBHF(Variable Blank Holder Force) optimization strategy was employed to determine the optimal time-variable and spatial-variable BHF trajectories,aiming at improving the formability of automobile panels with aluminum alloy sheet.The strategy was implemented based on adaptive simulation to calculate the critical wrinkling BHF for each segmented binder of the Numisheet' 05 deck lid in a single round of simulation.The thickness comparison of the stamped part under optimal VBHF and constant BHF shows that the variance of the four sections is decreased by 70%,44%,64% and 61%,respectively,which indicates significant improvement in thickness distribution and variation control.The investigation through strain path comparison reveals the fundamental reason of formability improvement.The study proves the applicability of the new VBHF optimization strategy to complex parts with aluminum alloy sheet.

Deformation behavior of TC1 titanium alloy sheet under double-sided pressure

In order to investigate the influence of normal stress through thickness on the formability of sheet metal,the viscous pressure bulge(VPB)tests of an annealed TC1 titanium alloy sheet were carried out under two different conditions:double-sided pressure bulging and conventional single-sided pressure bulging.The automated strain analysis,measurement environment(ASAME)and scanning electron microscope(SEM)were used to study the strain distributions and the fracture morphology of bulged specimens.It is found that thickness strain is increased for double-sided pressure bulging specimens,and the limiting dome height(LDH)of double-sided pressure bulging specimens is increased by 31.8% compared with conventional single-sided pressure bulging specimens.The dimples in fracture surface for double-sided pressure bulging specimens are larger and deeper than those for conventional single-sided pressure bulging specimens.The results indicate that normal stress through thickness is helpful in improving the formability of titanium alloy sheet metal.

Texture evolution of extruded AZ31 magnesium alloy sheets

The evolution of texture during the annealing and hot rolling process of extruded AZ31 magnesium alloy sheets was studied. There are two kinds of texture components in the extruded AZ31 sheets. One is {0002}<1010> and the other is {1010}<1120>. The {0002}<1010>component predominates. After annealing at 723 K for 3 h, both {0002}<1010> and {1010}<1120> components are strengthened moderately. This indicates that grains with both two components mentioned above grow faster than those with other orientations. The {1010}<1120> component disappears and the intensity of {0002}<1010> component decreases significantly after hot rolling with a 30% reduction at 623 K. This is mainly attributed to rotational dynamic recrystallization (RDX) during the hot rolling.

Novel algorithm for determining optimal blankholder forces in deep drawing of aluminum alloy sheet

Wrinkling and fracture are main defects in sheet metal forming of aluminum alloy sheet,which can be reduced or even eliminated by manipulating a suitable blank -holder forces (BHF). But,it is difficult to attain the optimum BHF during she et metal forming. A new optimization algorithm integrating the finite element me thod (FEM) and adaptive response surface method is presented to determinate the optimal BHFs in deep drawing of aluminum rectangular box. To assure convergence,the trust region modes management strategies are used to adjust the move limit of design spaces. Finally,the optimum results of rectangular box deep drawing a re given. Verification experiments are performed to verify the optimal result.

Analysis of surface orange peel of aluminum-alloy automobile sheet by using of EBSD and X-ray diffraction

The formation cause of orange peel of aluminum-alloy automotive sheet after tensile deformation was analysed by using X-ray diffraction and electron back-scattered diffraction(EBSD).The test results showed that formation cause of surface orange peel after tensile deformation related to product texture and nonuniform deformation during the tensile process.The grain size has significant effect on deformation uniform and texture formation.Coarse grains were easy to produce nonuniform deformation and texture,which would produce surface orange peel after tensile deformation.