Formability Index Research Articles

First and third generations of advanced high-strength steels in a FeCrNiBSi system

Three different solidification routes (slow, accelerated and fast) and a two-step heat treatment process were applied to a FeCrNiBSi alloy system to introduce new candidates for advanced high-strength steels (AHSSs). The evolution of the microstructure after hot roll, heat treatment, and tensile deformation was characterized using optical and electron microscopy techniques, as well as hardness and room temperature uniaxial tensile tests. The increase in the initial strain-hardening rate (strain incompatibility of microstructure components) due to grain refinement as a consequence of fast casting cooling rate results in higher mechanical properties in fast-cooling specimens with a formability index of 18.00–37.80 GPa%. Deformation-induced precipitation in the as-rolled fast-cooling specimen and transformation-induced plasticity, microband formation, and austenite grain rotation in the heat-treated fast-cooling specimen are the main dissipation energy mechanisms. The heat-treated accelerated-cooling and slow-cooling specimens with formability index of 4.75–25.50 and 2.34–14.60 GPa%, respectively, are competitive with transformation-induced plasticity, dual-phase, and complex-phase AHSSs.

Microstructural evolution and mechanical properties of a novel FeCrNiBSi advanced high-strength steel: Slow, accelerated and fast casting cooling rates

In the current work, three different solidification routes and a two-step heat treatment process were applied to a novel FeCrNiBSi alloy system to introduce a new candidate for advanced high-strength steels. The evolution of the microstructure after solidification, heat treatment, and tensile deformation was characterized using optical and electron microscopy techniques, as well as hardness and room temperature uniaxial tensile tests. The effects of the different solidification routes and heat treatment parameters on the deformation and fracture mechanisms of this steel are discussed. Grain refinement, precipitation hardening, and solid solution as a result of the fast casting cooling rate led to an increase in strength at improved ductility. This result can be explained partly by the less severe stress/strain partitioning at the matrix grain/M2B interfaces and better interface cohesion. Moreover, the stress/strain partitioning characteristics between the matrix grains and M2B led to a higher initial strain hardening rate. The fast casting cooling rate further promoted ductile fracture mechanisms, which is a result of increased cleavage fracture stress. The higher casting cooling rate and two-step heat treatment resulted in a strong increase in formability index, from 8GPa% to 24GPa%, at which the mechanical properties occupy the TRIP envelope. Heat treatment of the fast-cooling specimens led to a small reduction in yield and tensile strength and 22% total elongation percentage improvement (from 10% to 32%).

Production of nanostructure copper by planar twist channel angular extrusion process

This study challenges experimentally, the feasibility of new severe plastic deformation method entitling planar twist channel angular extrusion (PTCAE) for fabrication of nanostructure pure copper. The results indicated, deformed copper has 71%, 69% and 113% higher yield strength, ultimate tensile strength and hardness magnitude as compared to the as-received condition. Additionally, the fractography of tensile sample showed the mechanism alteration from multiple dimples to cleavage planes, associating the production of brittle type material. Moreover, the reduction of bulk formability index of the processed copper in comparison with the initial condition confirms the decrease of material ductility due to the strain hardening and grain refinement phenomena. The grain size of about 270 nm is also attained after the single pass processing. Eventually, a grain size correction coefficient is proposed to the strength to hardness ratio as a rule of thumb for estimation of strength by means of hardness irrespective of the grain size of the pure copper material.

The Effect of SiC Particle Addition During FSW on Microstructure and Mechanical Properties of AZ31 Magnesium Alloy

Welding and joining of magnesium alloys exert a profound effect on magnesium application expansion, especially in ground and air transportations where large-size, complex components are required. Due to specific physical properties of magnesium, its welding requires great control. In general, the solid-state nature of friction stir welding (FSW) process has been found to produce a low concentration of defects. In the current research, specimens from AZ31 magnesium alloy were welded together using the friction stir process with previously inserted SiC powder particles in the nugget zone. In other words, during the FSW process, the pre-placed SiC particles were stirred throughout the nugget zone of the weld. The results indicated that proper values of rotation and translation speeds led to good appearance of weld zone and suitable distribution of SiC particles producing increased weld strength. The comparison of the microstructures and mechanical properties of FS-welded AZ31 with those of FS-welded one using pre-placed SiC particles showed that the addition of SiC particles decreased the grain size and increased the strength and the formability index.

Microstructure Development and Mechanical Properties of Low-Silicon-Content TRIP-Assisted Steels after Coiling Process

In the present study, laboratory simulation of hot-strip rolling followed by coiling process was carried out in order to investigate the effect of bainite transformation on microstructure development and mechanical properties of low-silicon-content TRIP-assisted steels. Following a typical multistage isothermal deformation and cooling path, compression samples were quenched into a salt bath at various temperatures within bainite transformation range and held for different periods of time. The results indicated a decrease in either bainite holding time or temperature resulted in an increase in TS, whereas both T-El% and formability index have shown maximum values at some intermediate bainite holding temperature and time. Variation of TS with holding time was correlated to the fraction of martensite and microstructural coarsening whilst the changes in T-El% and formability index were appeared to follow the same trend as VRA. Additionally, the presence of thermal martensite provides a shielding effect on RA particles during straining, thereby postponing strain-induced transformation of austenite to martensite during subsequent deformation. Variations of T-El% and formability index with bainite holding temperature were also rationalized by considering the effect of bainite holding temperature on the characteristics of retained austenite and its surrounding matrix.

Quantitative formability estimation of ring rolling process by using deformation processing map

Studies on quantitative formability estimation by using deformation processing map have been performed to estimate deformation characteristics of SAF2205 duplex stainless steel during ring rolling process. To develop deformation processing map, dynamic materials model has been used on the basis of stress-strain relationships from Gleeble compression test. As a quantitative formability index, summation of ηij (efficiency of power dissipation for i-th unit deformation group in j-th slicing plane) multiplied by area fraction of unit deformation group (Aij) has been suggested. ηij-value for unit deformation group was determined from deformation processing map of which temperature and strain rate can be obtained by finite element method. For the feasibility analysis, the optimum blank dimension at various operating temperatures has been determined on the basis of formability index. The analysis result strongly confirms that the proposed formability index can provide a reliable guide in process design of ring rolling process.

Development and applications of forming-condition-based formability diagram for split concerns in stamping

This paper introduces an advanced, forming-condition-based formability diagram for accurately assessing the formability of complex stampings. The forming-condition-based formability diagram consists of a formability index that rationally define two curves (marginal line and safe line) and two zones (marginal zone and safe zone). The formability index measures deformation severity, tracks deformation history and predicts deformation trend. The safety factor, defined as the width of the marginal zone by means of the formability index, takes into account the forming conditions including deformation zone size, forming mode, bending process model, deformation history, metal flow pattern and post-necking deformation capacity of sheet metal. It is demonstrated that, rather than the traditional formability limit diagram, this formability diagram can more accurately quantify the formability status and can be used to determine the metal flow adjustment ranges for solving split problems. Its application to an automotive body side outer panel shows that it is a robust tool for formability engineering and troubleshooting through using numerical simulations and/or circle grid analysis.

Effect of Solution Heat Treatment Conditions on the Mechanical Properties and Formability for AA 2024 Alloy

The properties of the heat-treatable aluminum alloys are enhanced by solution heat treatment and controlled ageing. The mechanical properties become stable with natural ageing at room temperature within a few days for some heat-treatable alloys, especially 2XXX series, considerable changes of the properties occur even after many years for some of them. Solution heat treatment of AA 2024 is very critical and sensible and therefore it should be carefully conducted. In this research, the effects of the solution temperature, soak time, quenching delay and heating rate of AA 2024 on the mechanical properties and the formability index (limiting dome height) were investigated in order to determine optimal solution heat treatment condition. Mechanical properties were determined and limiting dome heights of the formed parts were measured for all the situations and optimal solution heat treatment conditions were determined by using ANOVA method.

Non-Isothermal Resistance Heating for Hot-Stamped Parts with Tailored Properties and Tempering Treatment on Directly Hot-Stamped Parts

Non-isothermal resistance heating in the hot stamping of quenchable steel sheets was developed to produce ultra-high strength steel formed parts with tailored properties. The heating temperature of parts is related with width of samples heated by resistance heating. With the same input energy, the strength in the narrow portions is high owing to the high energy density and that in the wide portions is low owing to the low energy density. Hat-shaped products having a tensile strength arrange from 600 MPA to 1800 MPa were formed. The tempering treatment on the directly hot-stamped boron steel resulted in better mechanical properties and higher formability index. The SEM figures indicates that the nano-carbide formation during the tempering treatment were suggested as the evident reasons for the occurrence of the mentioned robust properties. Finally the combination of temperature 250 ℃ and holding time 45 min can achieve the best comprehensive mechanical properties.

Effect of Sintering Time Variations on Stress Based Pore Closure Rate Studies on Al-SiC P/M Composites During Cold Upsetting

The aim of the present investigation has used to predict the stress formability index and the pore closure behavior of the sintered Al-SiC composites. Aluminium composite powder reinforced by silicon carbide containing 10% and 20% SiC. Three different sintering time intervals were proposed namely 1.5, 3 and 4.5 hrs at 605°C were completely investigated. The effect of SiC addition on the formability stress index value was studied. For higher SiC addition preforms the formability stress index reaches very high value. With increasing sintering time the formability stress index increases due to a decrease pore. It was enlightened to obtain a pore closure verification three novel stress based pore closure rate indices were proposed and analysed for all the above said preforms and their variations with respect to their relative density were plotted and discussed. The Formability stress index value were evaluated and discussed in terms of matrix and geometric work hardenings.

The effect of SiC/Al2O3 particles used during FSP on mechanical properties of AZ91 magnesium alloy

Abstract Friction stir processing, as a method of changing the properties of a metal, through intense, localized plastic deformation, has been developed based on the basic principles of friction stir welding. In the current research, mechanical properties of AZ91 magnesium alloy were modified by the application of friction stir processing. Surface composites using SiC as well as Al2O3 nano-particles were developed. Yield and tensile strengths as well as hardness values of specimens were measured. The results showed that friction stir processing modified the size of grains noticeably and improved the mechanical properties. The results also indicated that SiC particles were more beneficial than Al2O3 particles with regard to improvement of the properties. It was also concluded that homogeneous distribution of particles resulted in the decrease of grain sizes to 3 μm and the increase in strength and formability index to 390 MPa and 6 500 MPa, respectively.

Formability Estimation of Ring Rolling Process by using Deformation Processing Map

Quantitative formability estimation by using deformation processing map have been performed to estimate deformation characteristics of SAF2205 duplex stainless steel during ring rolling process. To develop deformation processing map, dynamic materials model has been used on the basis of stress-strain relationships from Gleeble compression test. As a quantitative formability index, summation of ηij(efficiency of power dissipation for i-th unit deformation area in j-th slicing plane) multiplied by unit deformation area fraction(Aij) has been suggested. ηij-value for unit deformation area was determined from deformation processing map of which temperature and strain rate can be obtained by finite element method. For the feasibility analysis, the optimum blank dimension at various operating temperatures has been determined on the basis of formability index. The analysis result strongly confirms that the proposed formability index can provide a reliable guide in process design of ring rolling process.

Microstructure and mechanical properties of commercially pure aluminum processed by accumulative back extrusion

Accumulative back extrusion (ABE), as a new severe plastic deformation (SPD) method, was applied on a commercially pure aluminum, resulting in an ultrafine microstructure. The grain refinement was attributed to the shearing and/or to the mechanical partitioning of the initial coarse grains as well as different dynamic recrystallization mechanisms (i.e., discontinues and continues ones). The effects of imposing several passes along with the strain reversal path method during consecutive ABE passes were discussed. Mechanical characterization revealed that the yield and ultimate strength of pure Al were significantly increased through applying ABE. This was related to grain boundary and dislocation strengthening, as well as to Orowan dislocation bowing mechanisms. The elongation, however, was deteriorated after ABE processing. This was interpreted through the lack of ability of the material to accommodate the ABE-induced strain, inhomogeneous distribution of strain across the ABE-processed workpieces, and the reduced work hardening capacity of the fine-grained aluminum. The formability index and static toughness were also considered to verify the overall mechanical performance of the ABE-processed pure Al.

Evaluation of Erichsan Number and Peak Load of Sheet Metals

The formability characteristics such as Erichsan number and peak load can be determined through the Erichsan cupping test. This test is inverted deep drawing with stretching methodology. In this test a spherical punch is used to evaluate the formability characteristics of sheet metals. In deep drawing process the sheet is formed to cup shape. Due to punch force, the tensile forces produced sheet metal and it is stretched radially, but it circumferentially compressed as its diameter decreases. If these stresses reach critical level characteristics of the material thickness, it causes slight undulations known as buckles. Buckles may develop into more pronounced undulations or waves known as wrinkles. Formation of wrinkles in cup depends on blank holding pressure. In Erichsan cupping test, a single specimen with required dimension drawn into cup until the fracture occurred at dome of cup by the force applied through continuous movement of hemispherical punch into specimen of sheet metal. In this test the cup height at fracture and peak load is measured. These are used as a measure of the formability index. Cup height at fracture in ‘mm’ is measured as Erichsan number. Cup height at fracture is used as the measure of stretchability. The formability can be expressed as erichsan number and peak load. In this test the formability characteristics of sheet metals such as alloys of aluminum, mild steel, titanium and also cartridge brass are studied through finite element analysis. The formability characteristics are can be evaluated through different formability tests. The tests are intrinsic tests and simulative tests. In the category of simulative tests such as bending tests, drawing tests, stretching tests and combined mode of tests. The formability characteristics of different sheet metals such as erichsan number and peak load can be studied from erichsan cupping tests. This test is under the category of stretching and drawing test [1-2]. Deep drawing is a compression-tension forming process. In this process the blank is generally pulled over the draw punch into the die; the blank holder prevents the wrinkling taking place in the flange. There is great interest in the process because there is a continuous demand on the industry to produce light weight and high strength components. Design in sheet metal forming, even after many years of practice, still remains more an art than science. This is due to the large number of parameters involved in deep drawing and their interdependence. These are material properties, machine parameters such as tool and die geometry, work piece geometry and working conditions. Research and development in sheet metal forming processes requires lengthy and expensive prototype testing and experimentation in arriving at a competitive product. The overall quality and performance of the object formed depends on the distribution of strains in the sheet material. Material properties, geometry parameters, machine parameters and process parameters affect the accurate response of the sheet material to mechanical forming of the component [3-5]. The effect of material properties on formability as the properties of sheet metals varies considerably, depending on the base metal ( steel, aluminum, copper, and so on), alloying elements present , processing , heat treatment, gage, and level of cold work. In selecting material for particularapplication, a compromise usually must be made between the functional properties required in the part and the forming properties of theavailable materials. For optimal formability in a widerange ofapplications, the work materials should: distribute strain uniformly, reach high strain with out fracturing, with stand in plane compressive stresses with out wrinkling, with stand inplane shear stresses without fracturing, retain part shape upon removal from the die, retain a smooth surface and resist surface

Enhanced Mechanical Properties of a Hot-Stamped Advanced High-Strength Steel via Tempering Treatment

The hot stamping process has an extensive range of applications due to its advantages over the traditionally used stamping techniques developed in the past. To enhance the mechanical properties of the indirectly hot-stamped parts, the quenching and partitioning (Q&P) process has been recently applied on boron-alloyed steel. In the current research, it was observed that the tempering treatment on the directly hot-stamped boron steel resulted in better mechanical properties and higher formability index compared with the reported results using the Q&P process. The nano-carbide formation and the dislocation annihilation during the tempering treatment were suggested as the evident reasons for the occurrence of the mentioned robust properties. The ease of the practical implementation of the tempering route together with the markedly enhanced mechanical properties of the tempered parts make the suggested method privileged. Additionally, the variations in the yield strength before and after tempering were quantitatively evaluated.

Influence of heat treatment on the microstructure, texture and formability of 2024 aluminium alloy

We have investigated the effect of heat treatment on the microstructure, texture and formability of high-strength aluminium Al2024 sheets of gauge thicknesses 1.27mm and 2.03mm. Both optical and electron microscopy were employed to characterise the microstructure. Tensile tests performed at 0°, 45° and 90° to the rolling direction were used as an indication of the anisotropic behaviour of the sheets. The formability of the sheets was assessed by performing stretch forming tests over a hemispherical punch. Comparison of microstructure and material properties indicated an effect of precipitation hardening on the overall anisotropy of the investigated materials. We report an improvement in the total elongation under uniaxial tension with a loss in strength for 2.5h and 2 days ageing while the ageing treatment for 1 week (peak hardness) resulted in increased strength with a decline in total elongation. The 1.27mm thick sheet showed better drawability and least tendency to earing than the thicker sheet. The drawability was the highest at 45° to the rolling direction for the as-received material and those that had been aged for 2.5h and 2 days. Forming limit diagrams derived from the stretch forming tests showed that the 2 days aged sample had the highest plane strain limit making it the most appropriate condition considering that the plane strain is usually the most critical forming strain in stamping applications. In addition, the 2 days aged sample had its plane strain shifted towards the biaxial stretching area which is likely to have a positive effect on some sheet forming applications. Finally, a formability index was calculated and compared against the hardness plot.

CAR process: A technique for significant enhancement of as-cast MMC properties

Abstract Continual annealing and roll-bonding (CAR) process was used in this study as a very effective method for improving the microstructure and mechanical properties of the A356/SiC metal matrix composite produced by semi-solid metal processing. The results showed that the increase in the number of cycles led to the following points: (a) the uniformity of the silicon and silicon carbide in the aluminum matrix was improved, (b) the Si particles became finer and more spheroidal in appearance, (c) the porosity was decreased, (d) the bonding quality between the reinforcement (SiC particles) and the matrix (A356 aluminum) was improved, (e) the particle free zone disappeared, and therefore (f) the tensile strength, elongation, and formability index of the samples were improved. The microstructure of the manufactured A356/SiC composite after ten cycles indicated a totally modified structure so that its tensile strength, elongation, and formability index values reached 166.7 MPa, 23.9%, and 3984 MPa·% which were 1.74, 4.19, and 7.29 times greater than those of the as-cast composite, respectively.

Comparison of the Microstructure and Mechanical Properties of As-Cast A356/SiC MMC Processed by ARB and CAR Methods

Accumulative roll bonding (ARB) and continual annealing and roll-bonding (CAR) processes were used in this study for improving the microstructure and mechanical properties of the A356/10 vol.% SiC metal matrix composite (MMC) produced by semi-solid metal processing (SSM). The results showed that using the ARB and CAR processes led to the following points: (a) the uniformity of the silicon and silicon carbide in the aluminum matrix improved, (b) the Si particles became finer and more spheroidal in appearance, (c) the porosity disappeared, (d) the bonding quality between the reinforcement and the matrix improved, (e) the particle-free zone disappeared, and therefore (f) the tensile strength (TS), elongation, and formability index of the MMC samples improved. However, it was found that the CAR process is a better method for improvement of microstructure and mechanical properties of as-cast MMC compared to ARB process.

Effect of Different Coiling Temperature on Mechanical Properties in Hot Rolled TRIP Steel

By means of optical microscopy(OM), scanning electron microscopy(SEM),X-ray diffraction(XRD),And tensile test, Mechanical Properties of hot rolled transformation -induced plasticity (TRIP) steels which were prepared through three different coiling temperature was investigated. Result reveals that the formability index of the experimental steel descends when the coiling temperature becomes low. Different coiling temperature has greater impact on retained austenite. Amount and carbon content of retained austenite in the experimental steel get less with lower coiling temperature.

Fabrication and characterization of Al/SiC p composites by CAR process

Metal matrix composite strips are conventionally produced by strip casting technology and ingot casting followed by secondary mechanical processes. These composites usually suffer from poor distribution of the reinforcement particles, presence of porosity, and unsuitable bonding between reinforcement and matrix, which result in low mechanical properties. In order to eliminate these problems, CAR (continual annealing and roll-bonding) process was used in this study as a very effective method for manufacturing Al/SiC p composite strip. The microstructure of the fabricated composite after fifteen CAR cycles showed an excellent distribution of SiC particles in the aluminum matrix without any noticeable porosity. The results also indicated that when the number of cycles increases, the tensile strength of the produced composites improves, but their ductility and formability index decreases at first and then increases. The tensile strength and formability index of the fifteen cycle CARed composite were 1.58 and 1.23 times higher than those of the initial alloy, respectively, while the elongation value decreased slightly.