Interstage Annealing Research Articles

Assessment of different processing strategies to fabricate bulk Mg-Fe nanocomposites

Recent observations indicate that very high deformation temperatures (673 K corresponding to 0.7 of Mg's melting point) by high pressure torsion (HPT) are mandatory to successfully synthesize bulk Mg-Fe nanocomposites with homogenous microstructure and exceptionally high strength (2.2 GPa Hardness). This spurs the development of new fabrication strategies to further strengthen the material while maintaining microstructural homogeneity for lower processing temperatures (T < 673 K). In this regard the present work deals with various strategies of severe plastic deformation at temperatures below 673 K including ball milling the Mg50Fe50 powder followed by HPT, HPT at 673 K followed by HPT at room temperature, inter-stage annealing during deformation, and changing the geometry of HPT anvils. Microstructural analysis using a scanning electron microscope and results of microhardness tests revealed that although abovementioned strategies accelerated microstructural refinement in Mg-Fe composites, strain localization cannot be suppressed. The strain localization and consequently inhomogeneous microstructure can be attributed to the immediate strengthening of basal texture intensity in Mg phase at low temperature driven by shear strain. Hence, the lack of structural reproducibility and hardness values less than 2.2 GPa show that all strategies are not sufficiently effective to synthesize bulk Mg50Fe50 nanocomposites. Only a high deformation temperature is the main key to fully transform a coarse structure into a homogeneous nano-structure with exceptional strength and good reproducibility.

AUSTRAL WRIGHT COPPER ALLOY 220 (UNS C22000)

Abstract Austral Wright Copper Alloy 220 (UNS C22000), also known as 90/10 gilding metal, is a wrought copper-zinc alloy. It combines a rich golden color with the best combination of strength, ductility, and corrosion resistance of the plain copper-zinc alloys. It weathers to a rich bronze color and can be supplied in pre-patinated colors ranging from deep brown to green. Austral Wright Copper Alloy 220 has a lower rate of work hardening than the copper-zinc alloys with higher zinc content, such as alloys 260 and 272. This is an advantage in multistage pressing applications without interstage annealing. It has excellent deep drawing characteristics and resistance to pitting corrosion when exposed to severe weather and water environments. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: Cu-935. Producer or source: Austral Wright Metals.

Development of a new stainless austenitic CrMnNi steel using TRIP/TWIP effect for a high cold formability

AbstractA new austenitic stainless CrMnNi steel with a high cold formability coupled with high strength was developed. The cold formability is based on the distinct transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP). Thereby a maximum of strain is reached nearby room temperature. Using the TRIP/TWIP effect of CrMnNi steel a cost‐ and energy‐efficient production of thin sheets is enabled by a reduced number of interstage annealing. Thin sheets with thicknesses from 0.1 mm till 1.25 mm were cold‐rolled industrially and there properties compared to conventional CrNi steel 1.4301 (AISI 304) and CrNiMo steel 1.4404 (AISI 316 L).Plate and lamellae heat exchangers of CrMnNi thin sheets were produced under industrial conditions. The form stability of the plate heat exchangers was increased by 47 % and the component failure pressure raised by 45 % at room temperature. Based on its high strength it is suggested to apply the new austenitic CrMnNi steel in lightweight constructions. Although the nickel content was reduced by 50 % to 65 % compared to conventional steels 1.4301 and 1.4404 the corrosion resistance of the CrMnNi steel is comparable with conventional CrNiMo steel 1.4404.

Influence of second phase particles on corrosion resistance of N36 alloy in superheated steam

The nodular corrosion resistance of N36 (Zr–0.8Sn–1Nb–0.3Fe–0.12O, wt%) alloy with different temperatures of interstage annealing and optimized Zircaloy-4 (lower content of tin) cladding tubes were tested in 500 °C and 10.3 MPa superheated steam. The result showed that no nodular spots appeared on surface of N36 alloy cladding tubes after 500 h corrosion, while nodular spots on optimized Zircaloy-4 tubes after 8 h. The differences of weight gain between two kinds of N36 tubes suggested that the percentage (volume fraction) of tetragonal Zr dioxide in oxide film can be effectively influenced by characteristics, such as size, of the second phase particles on the oxide film-matrix boundary. The analysis by SEM and LRS clearly indicated that smaller and fine distributed second phase particles were beneficial to stabilize the oxide via endure the uniform stress so it could slow down the altering process from tetragonal Zr dioxide to monoclinic Zr dioxide.

Effects of hot rolling and inter-stage annealing on the microstructure and texture evolution in a partially homogenized AZ91 magnesium alloy

The evolution of microstructure during hot rolling and inter-stage annealing of a partially homogenized AZ91 magnesium alloy was investigated by microscopic examination and micro-texture analyzing. The effects of key processing parameters including rolling temperature, rolling speed, number of rolling passes and inter-stage annealing treatment on the deformation mechanism and recrystallization behavior of the experimental alloy were studied. At lower rolling temperature, the plastic strain applied during rolling was accommodated by the formation of twin and shear bands whereas at higher temperatures non-basal slip systems were activated resulting in the suppression of twinning and, hence, slip became the dominant deformation mechanism in such rolling conditions. The process facilitated an effective grain refinement by both dynamic and static recrystallization phenomena with an increase in the number of rolling passes and conducting inter-pass annealing stages leading to a reduction of average grain size to below 10μm. Moreover, optical microscopic examinations for all the rolling conditions demonstrated that twin DRX was the major dynamic recrystallization mechanism at the beginning of the rolling process due to the large initial grain size. However, new grains were found to nucleate preferably at grain boundaries as the average grain size decreased during the hot rolling process. Micro-texture analysis for all the processing conditions showed a relatively strong basal texture produced after the first pass of rolling, which was then weakened during the subsequent annealing and rolling stages.

Fabrication and characterization of nano/amorphous dual-phase FINEMET microwires

• Nano/amorphous dual-phase FINEMET microwire was fabricated and characterized. • The unique dual-phase structure is correlated to its different cooling experience. • The extracted microwires possess high tensile strength over 1800 MPa. • Excellent EMI property was elucidated by the multiple magnetic loss mechanisms. A nano/amorphous dual-phase FINEMET microwire was fabricated directly from molten alloy without any interstage annealing by a home-built melt extraction technique (MET). The microstructure, mechanical and pronounced electromagnetic interference shielding (EMI) effectiveness of this dual-phase microwire has been systematically evaluated. The structural analysis reveals that the as-cast FINEMET microwire consists of two distinct structures, i.e., amorphous and nanocrystalline phase due to their different cooling characteristics. Compared with other reported FINEMET alloys, the extracted microwire exhibits a superior high tensile strength of 1800 MPa. These nanocrystals enabled dual-phase microwires also exhibit large EMI SE values in the frequency range of 8–12 GHz (X-band) due to the multiple magnetic loss mechanisms associated with their intrinsic structural characteristics. The combination of excellent mechanical properties and electromagnetic properties make this kind of melt-extracted dual-phase FINEMET microwire promising for a range of structure and multifunctional applications.

Softening interstage annealing of austenitic stainless steel sheets for stamping processes

To study the mechanics of work-hardening and annealing-softening, a series of experiments were conducted on samples of 304 austenitic stainless steel sheets. In addition, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and tensile testing were carried out to study changes and mechanisms of the stainless steel structures and properties during work-hardening and annealing-softening. The results indicate that annealing at low temperatures (100–500 °C) can only remove partial residual stresses in the sample and the softening via annealing is not obvious. Bright annealing and rapid cooling in a protective atmosphere can completely soften the cold-worked material. In addition, the low-temperature sample without a protective atmosphere only has a little oxidation on the surface, but at higher temperature the oxidized layer is very thick. Thus, high-temperature annealing should include bright annealing.

Modelling the Effect of Pre-Strain and Inter-Stage Annealing on the Stretch Forming of a 2024 Aluminium Alloy

The severe double curvatures often encountered in aerospace fuselage and nacelle skins often necessitate multistage stretch forming operations. Each stage adds value to the component and rejection, particularly at later stages, must be avoided. Therefore process optimisation using accurate modelling tools to predict the strain levels is essential. This paper presents a novel method for modelling the aforementioned stages of the process using a tailored material model based on strain history and heat treatment. The modelling process is implemented within the PAMSTAMP Finite Element code, by modifying the material properties in the input file using an Excel based algorithm. The proposed method is validated using profiled stretch formed specimens, thereby imposing a variable strain gradient in a single specimen without having to resort to the complexity of double curvature. The model results are shown to represent the observed behaviour well.

The Effect of Pre-Strain and Inter-Stage Annealing on the Formability of a 2024 Aluminium Alloy

Stretch forming of both fuselage and nacelle skins often requires multi-stage processing to achieve the final form. Finding the optimum pre-strain level before inter-stage annealing is critical to avoid failure in subsequent processes and minimise the number of processing steps. This paper examines the effect of three pre-strain levels of 4%, 8% and 12%, followed by a recovery anneal process. Both yield behaviour and material formability are analysed. The forming limit diagrams indicate an immediate drop in formability in the pre-strained and annealed samples when compared with the O condition material. The aforementioned formability drop quickly saturates for the higher pre-strain magnitudes. This saturation is also evident in the uniaxial data. The underlying material texture, as described by the r-values, remains unchanged during processing, while the yield strengths are shown to increase in an almost isotropic fashion. Overall the paper indicates that to improve the formability in subsequent processing steps, the pre-strain levels should be maximized before the recovery anneal and second forming stage.

Consideration of the re-drawing of sheet metals based on finite-element simulation

The effects of the work-hardening characteristics of blank material, the first-stage drawing ratio, the tool shape and interstage annealing on the limiting re-drawing ratio have been considered, based on the results of the rigid-plastic finite-element simulation of the direct and reverse re-drawing processes. In an attempt to increase the drawing limit, re-drawing experiments have also been carried out using a partially thickened blank, the thickness of which is somewhat greater at the punch-head portion than at the flange portion. The simulation results show that the success or failure of the re-drawing process depends not only on the re-drawing ratio but also on the material and process parameters described above. It is predicted also that the difference in the limiting re-drawing ratio achieved by the direct and reverse re-drawing processes results from the severity of bending and unbending at the profile radius portions of the die and the cup holder. The use of a partially-thickened blank contributes appreciably to an increase in the drawing limit. For steel sheet, for instance, the total drawing ratio achieved by the first and second drawing processes can be increased from 2.94 for a normal blank with uniform thickness to 3.45 for a partially-thickened blank.

アルミニウム薄板の延性の向上に対する変形中の焼なましの影響

Interstage annealing is often employed as a method to increase the forming limit of sheet metals. This paper describes the effect of interstage annealing on the surface roughening and the improvement of limit strain of aluminum sheets. A rigid-plastic finite element simulation of plane strain tension was firstly made to predict how the limit strain could be increased by the interstage annealing and how the surface roughening would develop with plastic strain after the interstage annealing. Uniaxial tension, plane strain tension and hole expansion tests were then carried out to confirm the result of simulation. The simulation and experimental results show that the interstage annealing contributes to the recovery of ductility, but on the contrary, the increase in plastic strain due to the annealing causes the development of the surface roughening which induces a localized necking. As a result of these two effects which oppose each other, the total strain achieved is limited even if the number of interstage annealing is increased.

The effect of sheet thickness on the magnetic properties of 77 wt% Ni permalloys

The effect of sheet thickness,t, on the magnetic properties of some Ni-Fe alloys of approximate composition 77% Ni-14% Fe-5% Cu-4 wt% Mo for various heat treatments in the temperature range 300 to 1250° C has been investigated. The range of sheet thickness used was 50 to 375μm and was obtained by cold-rolling without interstage annealing. It was found that permeability increases with decreasing sheet thickness, attains a maximum att≃75μm and starts to fall as the thickness is further reduced. The increase in permeability with decreasing sheet thickness (t>75μm) is thought to be due to a decrease in eddy current losses, changes in texture formation and possibly the degree of short range order (SRO) developed in the material. The permeability obeys a 1/t 2 relationship with sheet thickness in the range 75 to 375μm. Below a sheet thickness of 75μm permeability starts to decrease with decreasing sheet thickness. The reason for this fall in permeability is thought to be due to a thickness dependent magnetostatic energy contribution to the wall energy associated with free poles along the domain wall and also to the loss ratio,η, which increases rapidly at small thicknesses. This rapid increase inη is due to factors such as the ratio of domain wall spacing to sheet thickness, which varies with sheet thickness, the spin relaxation term, which has a 1/t 2 dependence on sheet thickness, and the increase in the wall energy which increases the domain wall spacing. Finally a decrease in permeability could be caused by a different degree of SRO in the thinner specimens due to different cooling rates which could lead to an increase in first anisotropy constant,K 1, and saturation magnetostriction,λ s which then produces a decrease inμ i att<75μm when the degree of SRO in the specimens is not optimum.

Sheet-metal forming

Sheet-metal forming is gradually changing from a craft-based to an engineering-based process. The review acknowledges the metallurgical improvements that have been made in sheet metals and in tool steels, and concentrates on research aimed at understanding and describing the mechanical properties of sheet metals in a more quantitative manner. The need to forgo reliance on simple parameters, and to obtain more comprehensive data on plastic yielding and work hardening, is clearly recognized. The pronounced effect of the shape of the yield locus on the strain distribution in stretch forming and in deep drawing is discussed. Innovations and improvements in the engineering design of tooling now enable the production of long shells by deep drawing and redrawing, or by deep drawing and ironing, in a single stroke of the ram and without interstage annealing. Drawing into a pressurized fluid ensures greater control over deformation, and permits the forming of tapered shells in one operation, using thinner gauges than previously. General pressings are discussed with particular reference to galling problems, and to the different tooling requirements of various sheet metals.

The effects of interstage annealing in the stretch-forming of spherical-cap diaphragms of laminate construction

When sheet-metal laminates are formed, the degree of work-hardening may be so severe as to demand interstage annealing before the forming operation can be completed. This paper studies the simple case of the effects of the interstage annealing of laminates that are stretch-formed into spherical caps. Metallic spherical caps are formed products in their own right, being employed as safety-rupture diaphragms in the power and chemical industries. During the commercial production of safety-rupture diaphragms, the traditional parameters available to the designer are (a) disk material properties, (b) disk shape, (c) disk dimensions in the plane of the sheet and (d) disk thickness. It is suggested that extra flexibility is obtainable by heat-treatment of the diaphragm subsequent to initial doming. By an appropriate amount of initial doming, the final bursting pressure of a diaphragm can be reduced to the desired level. Theoretical predictions are verified experimentally.

Influence of interstage annealing on the stretch formability of sheet metal laminates: Beese, J.G. Trans ASME J Engng Mater and Tech Vol 99 series H No 1 (January 1977) p 42

Influence of interstage annealing on the stretch formability of sheet metal laminates: Beese, J.G. Trans ASME J Engng Mater and Tech Vol 99 series H No 1 (January 1977) p 42

Influence of Interstage Annealing on the Stretch-Formability of Sheet-Metal Laminates

The interstage annealing of sheet-metal laminates is studied. A method of predicting the stretch-formability, as measured by the maximum possible uniform strain in simple tension, is proposed. Practical composite systems of potential commercial interest are examined. It is suggested that for certain sheet-metal laminates improved stretch-formability can be achieved as a consequence of a low-temperature, low-cost heat-treatment.

Theoretical Analysis for the Redrawing of Cylindrical Cups through Conical Dies without Pressure Sleeves

A theory for the redrawing of cylindrical cups through conical dies is presented. In the absence of a pressure sleeve a zone of unconstrained drawing exists prior to the conical zone and the principle of minimum energy is used to establish the extent of the zone and the associated deformation and stresses. A linearization of the von Mises yield criterion for plane stress problems is adopted and use of the flow rule associated with this criterion allows the variation of thickness across an element to be taken into account in the solution of the stress equilibrium equation; the strains can also be determined without resorting to numerical integration. Because the deformation during redrawing takes place in a series of discrete steps, work-hardening can be conveniently included in the analysis. Bending and unbending contribute significantly to the process work and a more detailed examination of the mechanism is justified. The present theory allows the effects of friction, die angle and die intersection radius to be examined but the punch load/redrawing ratio relation has been considered for only one die profile and clearance. The results for the redrawing of 70/30 brass cups with and without interstage annealing are compared with experimental redrawing loads and whilst excellent agreement exists for the near-limiting redrawing ratios, the theory considerably over-estimates the punch loads at the smaller ratios. A possible reason for the difference is discussed.