Effect of pre-twinning and heat treatment on formability of AZX311 Mg alloy

In this study,the effects of pre-strain-induced tensile twins(TTWs)and controlled heat treatment on the formability behavior of AZX311 Mg alloy sheets were investigated.A 4%compressive strain was applied to pre-strain the sheets using the in-plane compression(IPC)technique along the rolling direction(RD)to introduce TTWs.The pre-strained(PS)samples were subsequently heat-treated at 250℃,350℃,and 400℃ independently for 1 hr,and are termed as PSA1,PSA2,and PSA3,respectively.Erichsen cupping tests were conducted to assess the formability of the sheet samples under different initial conditions.The results showed that the PS sample heat-treated at 250℃ for 1hr exhibited a decrease in the Erichsen index(IE)compared to the as-rolled sample,whereas PSA2 and PSA3 samples showed an increase in IE values.Microtexture analysis revealed that most of the TTWs generated through pre-twinning were stable at 250℃;however,the twin volume fraction reduced to 41%at 350℃ compared to the PS samples due to enhanced thermal activity at that temperature.Furthermore,PSA2 samples showed severe grain coarsening in some areas of the sample,and the fraction of such grains increased in the PSA3 samples.The stretch formability(IE value)of PSA2 samples showed a 32.3%increase compared to the as-rolled specimens.Additionally,the analysis of the deformed specimen at failure under the Erichsen test indicated that considerable detwinning occurs in the PS and PSA1 samples,whereas dislocation slip activity dominates in the PSA2 and PSA3 samples during stretch forming.Apart from detwinning and dislocation slip,deformation twins were also observed in all samples after the Erichsen test.Thus,this work highlights the importance of texture control and its underlying mechanisms via pre-twinning followed by heat treatment and their impact on the room temperature(RT)stretch formability of AZX311 Mg alloy sheets.

Towards tailoring basal texture of rolled Mg alloy sheet by recrystallization for high room-temperature formability: A review

Room-temperature(RT) formability is a key factor to broaden the applications of rolled Mg alloy sheets in the industry. However, rolled Mg alloy sheets generally form strong basal texture, where the(0001) poles align parallel to the normal direction(ND). This hinders the activation of(0001) [1120] basal slip, limiting the RT formability. Therefore, texture weakening, i.e., the inclination of the(0001) poles from the ND, plays an important role to improve the RT formability. Recrystallization is crucial to control the textural development in Mg,and currently, the texture weakening is commonly achieved using static recrystallization(SRX). However, the type of slipping and twinning,which are activated during rolling, affect the textural features after SRX. It is also demonstrated that shear bands and preferential grain growth are important factors to tailor the texture during SRX. Indeed, dynamic recrystallization(DRX) easily occurs during rolling in Mg, which also affects the final rolling texture, while the effect of DRX on the textural formation is not extensively studied for the development of RT-formable Mg alloy sheets. Therefore, the effect of these factors on the textural development in rolled Mg is reviewed in this manuscript.Additionally, the ideal microstructure and texture for RT-formable Mg alloy sheets are still controversial. The RT-formability includes stretch forming(biaxial tension), bending(plane strain tension), and deep-drawing. In particular, the stretch forming is commonly used to evaluate the RT-formability of rolled Mg. Although the stretch formability has been improved by recent studies, the further improvement is necessary owing to the relatively low formability of rolled Mg compared with that of rolled Fe and Al. Based on the relationship between the microstructure/texture and stretch formability provided in the literature, the design guidance for high stretch formability is proposed in this review.

Comparative research on the formability of several ultra-high-strength steels

Three kinds of ultra-high-strength steels are subjected to uniaxial tensile,forming limit,and hole expansion tests to characterize their material forming properties.Results show that the elongation of S1500 reaches 12.9%and is higher than that of MS1500 with the same strength grade but is lower than that of QP980.The forming limit of S1500 steel is higher than that of MS1500 but lower than that of QP980.The instantaneous n-value of the material changes with the volume fraction of retained austenite.The hole expansion ratios of S1500,MS1500,and QP980 steels are 31.3%,32.2%,and 28.3%,respectively.The hole expansion ratio of QP steel increases slightly with the increase in strength grade.This behavior is contrary to the change trend of elongation and forming limit.Among the three kinds of materials,QP980 steel has the best global formability,and S1500 steel has better global formability than martensitic steel with a similar strength grade.The local formability of the materials improves slightly with the decrease in the amount of retained austenite.MS1500 may have the best local formability in accordance with engineering practice.

Enhancing plastic deformability of Mg and its alloys—A review of traditional and nascent developments

Mg and its alloys have continued to attract interest for several structural and super-sensitive applications because of their light weight and good combination of engineering properties.However for some of these applications,high plastic deformability is required to achieve desired component shapes and configurations;unfortunately,Mg and its alloys have low formability.Scientifically,the plastic behaviour of Mg and its alloys ranks among the most complex and difficult to reconcile in metallic material systems.But basically,the HCP crystal structure coupled with low stacking fault energies(SFE)are largely linked to the poor ductility exhibited by Mg alloys.These innate material characteristics have regrettably limited wide spread applicability of Mg and its alloys.Several research efforts aimed at exploring processing strategies to make these alloys more amenable for high formability–mediated engineering use have been reported and still ongoing.This paper reviews the structural metallurgy of Mg alloys and its influence on mechanical behaviour,specifically,plasticity characteristics.It also concisely presents various processing routes(Alloying,Traditional Forming and Severe Plastic Deformation(SPD))which have been explored to enhance plastic deformability in Mg and its alloys.Grain refinement and homogenising of phases,reducing CRSS between slip modes,twinning suppression to activate non-basal slip,and weakening and randomisation of the basal texture were observed as the formability enhancing strategies explored in the reviewed processes.While identifying the limitations of these strategies,further areas to be explored for enhancing plasticity of Mg alloys are highlighted.

Microstructure, mechanical properties and formability of friction stir welded dissimilar materials of IF-steel and 6061 Al alloy

AA 6061 alloy and interstitial-free(IF)steel plates were joined by the friction stir welding(FSW)method,and the microstructure,mechanical properties,and biaxial stretch formability of the friction stir welded(FSWed)parts were investigated.The results indicate that the FSWed parts showed optimum tensile strength during FSW with the 0.4-mm offset position of the tool.The Fe4Al13 intermetallic compound formed in the defect-free intersection of AA 6061 and IF-steel plates during FSW.The hardness of the IF-steel part of the FSWed region increased almost 90%relative to its initial hardness of HV0.2 105.The tensile and yield strengths of FSWed regions were approximately 170 MPa and 145 MPa,respectively.According to the formability tests,the Erichsen Index(EI)of the IF-steel,AA 6061,and the FSWed samples were determined to be 2.9 mm,1.9 mm,and 2.1 mm,respectively.The EI of the FSWed sample was almost the same as that of the AA 6061 alloy.However,it decreased compared with that of the IF-steel.The force at EI(FEI)was approximately 1180 N for the FSWed condition.This value is approximately 70%higher than that of AA 6061 alloy.

Texture and stretch formability of rolled Mg–Zn–RE(Y, Ce, and Gd) alloys at room temperature

To develop a new magnesium alloy with excellent formability at room temperature, the effect of Y, Ce, and Gd addition on texture and stretch formability of Mg-1.5Zn alloys was carried out. The result shows that Y, Ce, and Gd addition in Mg-1.5Zn alloys can effectively weaken and modify the basal plane texture, characterized by TD-split texture in which the position of basal is titled from normal direction （ND） toward transverse direction （TD）. When Mg-1.5Zn alloy with Gd addition appears low texture intensity and TD-split texture, where the position of basal poles is tilted by about 4-35° from ND toward to TD, the largest Erichsen value of 7.0 and the elongation rate reaches 29.1% in TD direction. However, Y and Ce addition in Mg-1.5Zn alloys promote a large number of second phase particles, which cancel the contribution of the unique basal texture to stretch formability and ductility.

Enhanced mechanical properties and formability of 316L stainless steel materials 3D-printed using selective laser melting

This study is conducted to develop an innovative and attractive selective laser melting(SLM)method to produce 316 L stainless steel materials with excellent mechanical performance and complex part shape.In this work,the subregional manufacturing strategy,which separates the special parts from the components using an optimized process,was proposed.The results showed that produced 316 L materials exhibited superior strength of^755 MPa and good ductility.In the as-built parts,austenite with preferred orientation of the(220)plane,δ-ferrite,and a small amount of CrO phases were present.In addition,the crystal size was fine,which contributed to the enhancement of the parts’mechanical properties.The structural anisotropy mechanism of the materials was also investigated for a group of half-sized samples with variable inclination directions.This technique was used to fabricate a set of impellers with helical bevels and high-precision planetary gears,demonstrating its strong potential for use in practical applications.

Effect of Interface Friction on Overlapping Sheets Bulging Formability and Microstructure of 5A02 Aluminum Alloy

Aluminum alloy 5 A02 with low plasticity was used as target sheet, and stainless steel SUS304 with good plasticity was used as overlapping sheet to investigate the effect of interface friction on bulging formability and microstructure of target sheet in overlapping sheets bulging process. Sheet sliding experiment was performed to measure interface friction coefficient of 5 A02/SUS304 in different lubricating conditions and normal pressure. Overlapping sheets bulging experiment of 5 A02/SUS304 was carried out to investigate the influence of interface friction on limit bulging height, wall thickness distribution, microstructure and fracture morphology of 5 A02 bulging specimens. The results showed that increase of the interface friction coefficient of 5 A02/SUS304 could effectively improve the limit bulging height and deformation uniformity of 5 A02. And the fracture style of 5 A02 transformed from toughness fracture of dimples-micropores gathered to fault slip separation fracture. Therefore, target sheet bulging formability is improved with the increase of interface friction coefficient.

Analysis of edge microstructural characteristics and stamping formability of low carbon pickled steel sheets

The microstructural characteristics and formability at the edges of low carbon pickled steel sheets have been investigated based on the generation of earing and cracking defects while drawing. The microstructure of the edge features coarse grains and mixed sized grains. The strength of the sheet edge is slightly lower than that at the center. Besides, the formability is obviously worsened. The plastic strain ratios along the longitudinal and transverse orientations are 0.31 and 0.6, respectively, with distinct anisotropy. The plastic strain ratio at the edge is obviously lower than that at the middle of the steel sheet. The observed microstructural characteristics and mechanical properties at the edge of the steel sheet can be attributed to the lower rolling temperature in the two-phase region of pro-eutectoid ferrite and austenite. These differences in microstructure and mechanical properties at the edge of the steel sheet lead to the generation of earing and cracking defects while drawing. The microstructure and mechanical properties at the edge of low carbon pickled steel sheets can be improved via the optimization of the rolling process and the adjustment of chemical composition.

Formability of AZ31 Mg alloy sheets within medium temperatures

The stretching tests of the commercial AZ31 Mg alloy were conducted at 130 ℃, 170 ℃, 210 ℃, at the forming speeds of 10 mm/min and 50 mm/min, respectively. The formability of AZ31 sheets at high temperature was evaluated by forming limit diagrams (FLD). The fracture morphologies were analyzed using a scanning electron microscope. The results show that the FLD of AZ31 Mg alloy is affected by the forming temperature, in another word, the formability increases with the increasing of the forming temperature. That may be because the non-basal slip system starts to move by thermal activation at high forming temperature. It is also demonstrated that the formability of the AZ31 Mg alloy is on the decline with the increasing of the forming speed. The slipping performs thoroughly to release the stress during the deformation if the forming speed decreases. In addition, the higher the forming temperature is, the more obvious the effect of the forming speed is. The forming temperature is the main dominating factor on the formability of AZ31 Mg alloy.

Investigation of Micro Formability of Bulk Amorphous Alloy in the Supercooled Liquid State Based on Fluid Flow and Finite Element Analysis

Research results on the viscous flow deformation behavior of bulk amorphous alloy in different systems are reviewed. The material exhibits an ideal Newtonian fluid at a high temperature. Analytical solution of lamellar fluid flow behavior is used to discuss the viscous flow behavior of the bulk amorphous alloy in the supercooled liquid state. A material model, which describes such deformation behavior of Mg6oCusoYlo amorphous alloy, is introduced into the finite element method of microformin8 process. Surface feature size was investigated and found not sensitive to the micro formability. Bulk amorphous alloy may possibly be applied to microelectro-mechanical-systems （MEMS） fabrication.

Development and Application of Universal Formability Technology

Using mathematical plasticity theories, universal formability (UF) technology has been developed and applied in the automotive stamping engineering and production. As a formability analysis tool, this technology is the major methodology for the development of stamping expert system (solution provider) for (a) product design and feasibility analysis, (b) material automatic selection using nomograms, (c) draw die design using pre-models, and (d) UF and robustness analysis of die performance in finite element analysis (FEA) environment.

Formability of Materials with Small Tools in Incremental Forming

Single point incremental forming(SPIF)is an innovative sheet forming process with a high economic pay-off.The formability in this process can be maximized by executing forming with a tool of specific small radius,regarded as threshold critical radius.Its value has been reported as 2.2 mm for 1 mm thick sheet materials.However,with a change in the forming conditions specifically in the sheet thickness and step size,the critical radius is likely to alter due to a change in the bending condition.The main aim of the present study is to undertake this point into account and develop a relatively generic condition.The study is composed of experimental and numerical investigations.The maximum wall angle(θmax)without sheet fracturing is regarded as sheet formability.A number of sheet materials are formed to fracture and the trends correlating formability with normalized radius(i.e.,R/To where R is the tool-radius and To is the sheet thickness)are drawn.These trends confirm that there is a critical tool-radius(Rc)that maximizes the formability in SPIF.Furthermore,it is found that the critical radius is not fixed rather it shows dependence on the sheet thickness such that Rc=βTo,whereβvaries from 2.2 to 3.3 as the thickness increases from 1 mm to 3 mm.The critical radius,however,remains insensitive to variation in step size ranging from 0.3 mm to 0.7 mm.This is also observed that the selection of tool with R<Rc narrows down the formability window not only on the higher side but also on the lower side.The higher limit,as revealed by the experimental and FEA results,diminishes due to excessive shearing because of in-plane biaxial compression,and the lower limit reduces due to pillowing in the bottom of part.The new tool-radius condition proposed herein study would be helpful in maximizing the formability of materials in SPIF without performing experimental trials.

Deformation Behavior and Formability of Gradient Nano-grained AISI 304 Stainless Steel Processed by Ultrasonic Impact Treatment

The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top layer was fabricated on coarse grains（CG） AISI 304 by ultrasonic impact treatment. The results showed that the CG substrate could effectively suppress the strain localization of NC in GNG layer, and an approximate linear relationship existed between the thickness of substrate（h） and uniform true strain before necking（ε_（unif））. Grain growth of NC was observed at the stress state with high Stress triaxiality T, which led to better ductility of GNG/CG 304 in SPT, as well as similar true strain after the onset of necking（ε_（neck）） compared with coarse 304 in tensile test. Ei-values of GNG/CG 304 with different structures were nearly the same at different punch speeds, and good formability of GNG/CG 304 was demonstrated. However, punch speed and microstructure needed to be optimized to avoid much lost of membrane strain region in biaxial stress state.

Evaluation of factors affecting the edge formability of two hot rolled multiphase steels

In this study, the effect of various factors on the hole expansion ratio and hence on the edge formability of two hot rolled multiphase steels, one with a ferrite–martensite microstructure and the other with a ferrite-bainite microstructure, was investigated through systematic microstructural and mechanical characterization. The study revealed that the microstructure of the steels, which determines their strain hardening capacity and fracture resistance, is the principal factor controlling edge formability. The influence of other factors such as tensile strength, ductility, anisotropy, and thickness, though present, are secondary. A critical evaluation of the available empirical models for hole expansion ratio prediction is also presented.

On the Formability of Some Metastable Alloy Phases

Pattern recognition and neural network methods have been used to investigate the formability of metastable alloy phases, It has been found that some chemi cal bond parameters Such as valence electron number, electronegativity and metallic radii of cor-nponent elements are the dominating fac tors affecting metastable alloy phase formation. Some semi-empirical rules found in this way may be useful for the construction of expert system for materials design.

Variations in microstructure and bending formability of extruded Mg–Al–Zn–Ca–Y–MM alloy with precompression and subsequent annealing treatment conditions

In this study, the bending formability of an extruded Mg–9Al–1Zn–0.3Mn–0.9Ca–0.6Y–0.5 MM(AZXWMM91100, wt%) alloy at room temperature is significantly improved through application of a combined precompression and subsequent annealing(PCA) treatment. As the amount of precompression applied along the extrusion direction(ED)(i.e., the total strain) increases from 4% to 6%, the area fraction of ED-oriented grains of the PCA-treated alloy increases, which consequently causes an improvement in its bending formability because these grains accommodate larger tensile strain along the ED during bending. As the temperature of the subsequent annealing treatment increases from 350 ℃ to 450 ℃, both the area fraction of the ED-oriented grains and the average grain size increase, and the residual dislocation density decreases owing to the promotion of boundary migration and occurrence of the recovery process at higher temperatures.Consequently, the bending formability of both the 4%-precompressed and the 6%-precompressed samples increases with an increase in the annealing temperature. However, when the precompressed samples are annealed at 300 ℃, their bending formability is lower than that of the extruded alloy because the dislocations formed by precompression remain even after the subsequent annealing at this temperature.

Regularities of formability of intermediate compounds in binary molten salt systems

The formability of intermediate compounds for thirteen kinds of binary molten salt systems, including 1 179 phase diagrams was discussed by pattern recognition method with bond parameters as features. These systems were MeX Me′X, MeX Me′X 2, MeX Me′X 3, MeX Me′X 4, MeX 2 Me′X 2, MeX 2 Me′X 3, MeX 2 Me′X 4, MeX 3 Me′X 3, MeNO 3 Me′(NO 3) 2, Me 2SO 4 Me′SO 4 (Me, Me′ denote metallic elements, X denotes halogen), Me AX B Me′ CX D (X is CrO 2- 4, WO 2- 4 or MoO 2- 4), and common cation systems MeX MeX′, MeX Me 2X′ (Me, Me′ denote metallic elements, X, X′ denote anion forming elements or radicals). It had been found that molten salt systems forming intermediate compounds and ones without intermediate compound distribute in different regions. Moreover, six general regularities for the formation of intermediate compounds in binary molten salt systems had been summarized on the basis of thirteen semi empirical models, which was obtained from the known phase diagrams.[

Effect of bending and tension deformation on the texture evolution and stretch formability of Mg-Zn-RE-Zr alloy

Bending and tension deformations were performed on Mg-1.3 wt%Zn-0.2 wt%RE-0.3 wt%Zr(ZEK100)alloy sheets that initially had a transverse direction(TD)-split texture.The effects of bending and tension deformations on the texture formation and room-temperature formability of specimens were investigated.The specimen subjected to 3-pass bending and tension deformations exhibited an excellent Erichsen value of 9.6 mm.However,the Erichsen value deterioration was observed in the specimen subjected to 7-pass deformations.The rolling direction-split texture developed on the surface with an increasing pass number of deformations.Conversely,the clear TD-split texture remained at the central part.As a result,a quadrupole texture was macroscopically developed with an increasing pass number of deformations.The reduction in anisotropy by the formation of the quadrupole texture is suggested to be the main reason for the improvement in stretch formability.By contrast,the generation of coarse grains near the surface is suggested to be the direct cause for the deterioration of the stretch formability of the specimen subjected to 7-pass deformations.