Shear-based deformation processing of age-hardened aluminum alloy for single-step sheet production

Shear-based deformation processing by hybrid cutting-extrusion and free machining are used to make continuous strip, of thickness up to one millimeter, from low-workability AA6013-T6 in a single deformation step. The intense shear can impose effective strains as large as 2 in the strip without pre-heating of the workpiece. The creation of strip in a single step is facilitated by three factors inherent to the cutting deformation zone: highly confined shear deformation, in situ plastic deformation-induced heating and high hydrostatic pressure. The hybrid cutting-extrusion, which employs a second die located across from the primary cutting tool to constrain the chip geometry, is found to produce strip with smooth surfaces (Sa < 0.4 μm) that is similar to cold-rolled strip. The strips show an elongated grain microstructure that is inclined to the strip surfaces – a shear texture – that is quite different from rolled sheet. This shear texture (inclination) angle is determined by the deformation path. Through control of the deformation parameters such as strain and temperature, a range of microstructures and strengths could be achieved in the strip. When the cutting-based deformation was done at room temperature, without workpiece pre-heating, the starting T6 material was further strengthened by as much as 30% in a single step. In elevated-temperature cutting-extrusion, dynamic recrystallization was observed, resulting in a refined grain size in the strip. Implications for deformation processing of age-hardenable Al alloys into sheet form, and microstructure control therein, are discussed.

Crystallographic texture of hot rolled uranium-molybdenum alloys

The uranium molybdenum (U-Mo) alloys have potential to be used as low enriched uranium nuclear fuel in research, test and power nuclear reactors. U-Mo alloy with composition between 7 and 10 wt% molybdenum shows excellent body centered cubic phase (γ phase) stabilization and presents a good nuclear fuel testing performance. Hot rolling is commonly utilized to produce parallel fuel plate where it promotes the cladding and the fuel alloy bonding. The mechanical deformation generates crystallographic preferential orientation, the texture, which influences the material properties. This work studied the texture evolution in hot rolled U-Mo alloys. The U7.4Mo and U9.5Mo alloys were melted in a vacuum induction furnace, homogenized at 1000°C for 5 h and then hot rolled at 650°C in three height reductions: 50, 65 and 80%. The crystalline phases and the texture were evaluated by X-ray diffraction (XRD). The as-cast and processed alloys microstructures were characterized by optical and electronic microscopies. The as-cast, homogenized and deformed alloys have γ phase. It was found microstructural differences between the U7.4Mo and U9.5Mo alloys. The homogenized treatment showed effective for microsegregation reduction and were not observed substantial grain size increasing. The deformed uranium molybdenum alloys presented α, γ, θ texture fibers. The intensity of these texture fibers changes with deformation step.

Dynamic and Post-Dynamic Recrystallization of Haynes 282 below the Secondary Carbide Solvus

Thermomechanical processes, such as forging, are important steps during manufacturing of superalloy components. The microstructural development during processing, which controls the final component properties, is complex and depends on e.g., applied strain, strain rate and temperature. In this study, we investigate the effect of process parameters on the dynamic and post-dynamic recrystallization during hot compression of Ni-base superalloy Haynes 282. Specifically, we address the effect of deformation below the grain boundary carbide solvus temperature. During deformation, discontinuous and continuous dynamic recrystallization was observed at the grain boundaries, and particle-stimulated nucleation occurred at primary carbides. Strain rate was determined to be the governing factor controlling the recrystallization fraction for strain rates up to 0.5 s−1 above which adiabatic heating became the dominating factor. Careful examination of the temperature development during deformation showed that the response of the closed-loop temperature control system to adiabatic heating can have important effects on the interpretation of the observed behavior. During a 90 s post-deformation hold, grain growth and an increasing fraction of twin boundaries significantly changed the deformation-induced microstructure and texture. The microstructure developed during post-dynamic recrystallization was mainly controlled by the temperature and only weakly coupled to the prior deformation step.

Prediction of Elastic Properties for Unidirectional Carbon Composites: Periodic Boundary Condition Approach

A three-dimensional finite element model of unidirectional fibre reinforced composites has been investigated numerically using periodic boundary condition method. This method was used to predict the elastic mechanical behaviour of a unit cell of such composites. Periodic boundary condition was used due to its capability to represent a single unit cell similar to the neighbouring unit cells with continuous physical elements. It is assumed that the paired nodes displaced continuously without separating or interrupting other nodes during the deformation step. From the study, it was revealed that the elastic modulus agreed well with the experimental results, indicating that the present model could be used effectively.

Structure Development and Deformation Behaviour of Pure Aluminium Processed by Constrained Groove Pressing

In this study, the relationship between the structure and properties of commercial purity aluminium alloy A1199 was investigated by applying constrained groove pressing (CGP) deformation method. The refinement of the coarse grain aluminium (Al) microstructure to sub microcrystalline size by large plastic strain at room temperature defined. The impact of various strains upon microstructure changes is investigated using transmission electron microscopy (TEM of thin foils) and electron back scatter diffraction (EBSD). A mixture of subgrains produced by grains subdivision and polygonized subgrains formed locally due to dynamic recovery was found in the deformed aluminium structure. The tensile properties and resulting hardness are related to microstructural evolution induced by constrained groove pressing deformation. A substantial impact of straining upon the increasing in tensile strength was observed after the first deformation step (first pass) Further strain increase had an insignificant effect on tensile strength but was accompanied by ductility loss. The post deformation annealing effect was then explored with aim to increase the ductility. The results indicate that changes in strength and ductility may be related to formation of a bimodal structure in deformed plates.

Novel Experimental Set-Up to Investigate the Wear of Coatings for Sheet Metal Forming Tools

The use of PVD and CVD coatings has increased significantly thanks to the improved tribological performances they offer in many metalforming processes. Nevertheless the proper coating selection for a specific forming operation is not well established yet, being mainly based on trails and error approaches. The use of FEM-supported analyses may represent an effective support in the optimization of process parameters, but the need of testing procedures and reliable models to describe the mechanical and tribological phenomena at the interface between the dies and the workpiece is still significant. The paper presents a novel experimental set-up for the evaluation of the wear resistance of dies coatings in sheet metal forming operations. A progressive stamping process was taken as reference case and analyzed by numerical analyses. Contact pressures, temperatures and tangential loads at the tools-blank interface were evaluated in each deformation step. TiAlN and CrN were selected as reference coatings and deposited via magnetron sputtering technique. The first part of the research was focused on the design of the novel set-up capable to carry out controlled wear tests in laboratory environment, performed with the parameters obtained from the numerical simulation. The results of such experiments were compared to the ones from standard laboratory tests and with industrial trials, though measurements of loads, of surface roughness evolution and by surface investigations trough Scanning Electron Microscope observations.

Thermomechanical analysis of an aircraft tire in cornering using coupled ale and lagrangian formulations

The thermomechanical behavior of an aircraft tire is predicted, using experimental devices, a model based on finite element software and an appropriate method of expressing the heat generated by skid in terms of the local friction coefficient, depending on the temperature. In the thermomechanical model, a steady state mechanical analysis is combined with a transient thermal problem. This combined approach is based on three main computing steps: the deformation step, the dissipation step and the thermal step. The deformation step calculates the stress and the velocity fields, which are used as inputs in the dissipation step to calculate the heat generated due to friction. The internal dissipation is assumed to be negligible. Finally, the thermal step yields new thermal maps based on the heat flux computed in the dissipation step. The coupling is established by updating the friction coefficient in the first two steps.

Thickness Effect on the Formability of AZ31 Magnesium Alloy Sheets

The thickness effect on formability of AZ31 magnesium alloy sheet has been widely investigated by means of uniaxial tensile tests, performed in the temperature range from 250 to 350°C, with strain rates varying from 10-4 to 10-1 s-1, using samples with different thickness values (from 1.5 to 3.2 mm). A preliminary microstructural study has shown that grain size and morphology are not significantly affected by both sheet thickness and heating just before the deformation step. The experimental results of tensile tests have been analysed in terms of flow curve shape, flow stress and strain to failure levels. They show that, in general, flow stress increases and ductility decreases with increasing sheet thickness even if such influence is strongly related to the temperature and strain rate conditions Finally, the analysis of the Zener-Hollomon parameter vs. peak flow stress data showed that the same mechanisms are operative in the investigated sheets.

Effect of Thermomechanical Processing Parameters on the Final Microstructure of Pipeline Steels

The phase transformation and the final microstructure were studied in a pipeline steel grade API-X80 by carrying out a number of physical simulations of the industrial hot rolling schedules. The deformation and the cooling parameters were simulated by means of hot torsion and dilatometry experiments. Torsion deformations in the same range as in the hot rolling schedule were applied in a multi-deformation cycle at various temperatures in the austenite region. Subsequently the following parameters were varied with respect to a reference status: the reheating temperature from 900 to 1200°C, the deformation step from 0.6 to 0.15 von Misses strain, the strain rate from 1 to 10 s-1, the inter-pass time from 0.4 to 2 s, the deformation temperature from 1,100 to 850°C, the cooling rate from 0.1 to 100°C/s and the cooling stop temperature from 650 to 25°C. The transformation product microstructures were observed with optical microscopy, scanning electron microscopy and electron backscatter diffraction. The experimental data were used to study the microstructure evolution of none-deformed austenite and highly deformed austenite (Von Misses strain of 3.2), and the corresponding CCT diagrams were constructed. The detailed microstructure characteristics obtained from the present work as well as the data from the CCT diagrams for undeformed and deformed austenite could be used to optimize the mechanical properties, strength and toughness of pipeline steel grades by thermo-mechanical control process.