Abstract

Four important commercial aluminum alloys, namely 1050, 5083, 6082 and 7010AA are processed through a single pass via two equal channel angular pressing (ECAP) dies with different geometries (die angles of 90° and 120°). Electron back scattered diffraction (EBSD) is applied on the flow plane of the processed samples. Large scans with a step size of 7 μm for grain size distribution and texture measurements, as well as small scans with a step size of 0.1 μm for determination of cell size distribution, were performed. Hardness and simple compression are employed to evaluate the mechanical properties of the ECAP processed samples. Shear bands in the ECAP processed 7010AA was a major feature that led to failure in all samples subjected to further simple compression. The hardness as well as the stress–strain behavior was similar in the ECAP processed 6082 and 5083AA. The die geometry and the strain involved in the single pass influenced the overall texture intensity developed in the wrought alloys (1050 and 5083AA) and had minimal influence on the texture intensity of the heat treatable alloys (6082 and 7010AA). Low angle grain boundaries dominated the microstructure of all alloys for all testing conditions.

Highlights

? Four different commercial aluminum alloys namely; 1050, 5083, 6082 and 7010AA are subjected to a single ECAP pass in two different dies. ? Evolution of mechanical properties (hardness, compression stress – strain response) were documented. ? Microstructure (grain size, cell size and misorientation angle, fraction of low angle grain boundaries) was quantitatively investigated. ? Texture (pole figures and ODF plots) and the intensity of texture fibers were quantified for all alloys.

Abstract

This paper presents an experimental analysis and a numerical simulation of the mechanical behaviour experienced by a steel rod during multiple-step wire cold-drawing processes. To this end, a set of tensile experiments is firstly carried out in order to characterise the material hardening evolution for different consecutive wire reductions. The experimental procedure also encompasses the measurement of drawing forces in a multiple-step process conducted at a laboratory scale under different drawing velocities. Then, this problem is simulated via a finite element formulation that accounts for both large viscoplastic strains and friction effects. The results obtained with the simulation are experimentally validated. Finally, the influence of specific operating conditions, such as the decrease of the number of wire reductions and the presence of back tension, on the material response during the whole process is numerically assessed.

Abstract

The alumina matrix ceramics used for drawing dies were prepared by hot-press sintering method. The ceramics materials were made of Al₂O₃/TiC, Al₂O₃/(W,Ti)C and Al₂O₃/Ti(C,N). Mechanical and friction properties of these materials were tested and measured. The experiments for testing friction properties were carried on wear and tear machine. Mechanisms of frictions were analyzed with scanning electron microscope. Results showed that the alumina matrix composite ceramics have good physical and mechanical properties for used as drawing dies. Measured friction coefficients of alumina matrix composite ceramics showed a trend of decline and kept the value of 0.4–0.5 with the rotating speed of 550 rpm. Alumina matrix composite ceramics have smaller wear rate, while the wear rates of Al₂O₃/TiC and Al₂O₃/(W,Ti)C decrease gradually with a rising rotation speed. The wear of alumina matrix ceramics was severe at deformation zone. The primary wear behaviors of alumina matrix ceramics are scraping and furrowing. Even though the mechanisms for wear different, abrasive and adhesive wear were found to be the predominant wear mechanisms for the ceramic drawing die.

Abstract

In the present paper, the copper-wire drawing process is analysed in order to optimise the die design and to obtain the best quality of wire. Different design parameters of the drawing process have been studied using FE-analysis and experiment. This study investigates the effect of the process variables such as semi-die angle and reduction in area, and the coefficient of friction on the drawing force value. For the wire, elastoviscoplastic behaviour is considered, while the die material is assumed to be elastic. Two types of dies have been used in this work: crystal mono diamond core (MD) and crystal poly diamond (PCD).

Experiments were carried out on drawing machine involving industrial conditions to measure the drawing force. The obtained results have been compared with analytical methods available in literature, particularly, with Siebel, Wistreich and Avitzur’s solutions.

Our results clearly indicate that friction has significant effects on the drawing force which decrease with the decrease of area reduction. The optimum die angle for wire drawing is assumed to be obtained when the plastic strain distribution across the diameter of the wire becomes uniform.

Abstract

This paper is concerned with the plastic energy absorption behavior of expansion tubes under axial compression by a conical–cylindrical die. The experiments and numerical simulation using FEM are presented in this paper. Experiments were conducted on circular 5A06 aluminum tubes with an internal radius fixed at 22.5 mm and different thicknesses between 1 and 5 mm; the tubes were pressed axially onto a series of conical–cylindrical dies each with a different semi-angle from 5° to 20°, where the radius of the cylindrical part was 24 mm. A numerical analysis was performed to investigate the tube deformation and the friction between the tube and die. A good fit of the experimental data was obtained by taking the value of the friction coefficient μ=0.05. Based on these experimental and numerical results, characteristics of driving force–stroke curves in different deformation modes are discussed in detail. Effects of tube dimensions and semi-angle of the die on steady-state force and energy absorption efficiency are also presented. Based on these experimental studies, a theoretical analysis to explain the deformation mechanisms of the tube expanded by a die is carried out and will be given in a subsequent paper [1].

Abstract

Severe plastic deformation studies of copper and Al–Cu alloy by multiple channel-die compression tests were investigated. The materials were tested under plane strain condition by maintaining a constant strain rate of 0.001/s. Extensive grain refinement was observed resulting in nano-sized grains after severe plastic deformation with concomitant increase in flow stress and hardness. The microstructural investigation of the severely deformed materials was investigated using optical microscope and scanning electron microscope. Shear band formation was identified as the failure mechanism in the two phase Al–Cu alloy. The results indicate difficulty in obtaining severe plastic deformation for alloys having two phase micro-structure.

Research highlights

? SPD of copper and Al–Cu alloy by multiple channel-die compression tests.? Extensive grain refinement resulting in nano-sized grains after SPD. ? Investigation of micro-structure using optical microscope and SEM. ? Shear band formation as the failure mechanism in the two phase Al–Cu alloy. ? Difficulty in obtaining SPD for Al–Cu alloy in this method.

Abstract

Advanced high strength steels (AHSS) are increasingly used in sheet metal stamping in the automotive industry. In comparison with conventional steels, AHSS stampings produce higher contact pressures at the interface between draw die and sheet metal blank, resulting in more severe wear conditions, particularly at the draw die radius. Developing the ability to accurately predict and reduce the potential tool wear during the tool design stage is vital for shortening lead times and reducing production cost. This paper investigates the effects of draw die geometry on the sheet metal tool wear distribution over the draw die radius using numerical and experimental methods. A numerical tool wear model is introduced and applied using the commercial software package Abaqus. Channel bend tests are carried out using an Erichsen sheet metal tester to verify the numerical model. Various geometries of radius arc profiles, including standard circular profiles, high elliptical profiles, and flat elliptical profiles, are numerically investigated, and the wear volume and contact pressure distribution along the radii are determined. The results show that the profile of the draw die radius has a significant effect on the wear distribution, and that a low contact pressure distribution can be achieved by using a combination of circular and high elliptical curved geometries.

Research highlights

? Investigation of advanced high strength steel as automotive stamping tool material. ? Predicting and reducing the tool wear in AHSS stampings to increase tool life. ? Effects of draw die geometry on the sheet metal tool wear distribution. ? An experimental methodology to validate the numerical model using channel forming. ? Low contact pressure predicted by combination of circular and elliptical geometries.

Abstract

Nanocomposite WC–8Co (mass%) powders with different CeB₆ contents were prepared using the planetary ball milling method. Effects of CeB₆ on the microstructures and mechanical properties of WC–8Co cemented carbides were investigated by X-ray diffraction, scanning electron microscope and mechanical properties testing. The results show that the grain growth and regularization of WC particles occur simultaneous with the addition of CeB₆. CeB₆ addition improves the density and fracture toughness and decreases the volume fraction of the η (Co₃W₃C) phase in the materials.

Abstract

Sub-micron size (0.4–0.6 μm) Co–Cu/Ni composite powders were synthesized by a co-precipitation method. The effects of minor Cu and Ni additions on the microstructure and the mechanical properties of ultrafine WC-10Co alloys were investigated using scanning electron microscope, X-ray diffraction and mechanical properties tests. The results show that Co–Cu binder phase refines the WC grains and increases the hardness of the base alloys. But the addition of Ni can't refine the WC grains and increase the hardness. The addition of minor Cu or Ni can improve transverse rupture strength of alloys through the solid solution strengthening. However, adding excess Cu can lead to the decrease in transverse rupture strength. With the partial substitution of Co by Cu and Ni, the hardness and transverse rupture strength of the alloys have a little change.

Research highlights

? The authors first reported the substitution of Co with Cu in the ultrafine grain hardmetals through the co-precipitation process. ? The research results show that the grain growth of WC particles of the based alloys was inhibited with the addition of Cu. ? Addition of Cu or Ni can improve transverse strength of alloys through the solid solution strengthening of Cu or Ni. ? The substitution of Co with Ni in fine-grained tungsten carbide cermets is assumed to be unsuitable due to WC grain growth. ? However, partial substitution of Co by Cu and Ni may be a very good method to solve the limitations of substitution of Co with Ni in fine-grained hardmetals.

Abstract

An Al₂O₃-based composite ceramic tool material reinforced with WC microparticles and TiC nanoparticles was fabricated by using hot-pressing technique. The cutting performance, failure modes and mechanisms of the Al₂O₃/WC/TiC ceramic tool were investigated via continuous and intermittent turning of hardened AISI 1045 steel in comparison with those of an Al₂O₃/(W, Ti)C ceramic tool SG-4 and a cemented carbide tool YS8. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results of continuous turning revealed that tool lifetime of the Al₂O₃/WC/TiC ceramic tool was higher than that of the SG-4 and YS8 tools at all the tested cutting speeds. As for the intermittent turning, tool life of the Al₂O₃/WC/TiC ceramic tool was equivalent to that of YS8, but shorter than that of the SG-4 at lower cutting speed (110 m/min). However, tool life of the Al₂O₃/WC/TiC ceramic tool increased when the cutting speed increased to 170 m/min, becoming much longer than that of the SG-4 and YS8 tools. The longer tool life of the Al₂O₃/WC/TiC composite ceramic tool was attributed to its synergistic strengthening/toughening mechanisms induced by the WC microparticles and TiC nanoparticles.

Wear resistance of alumina, alumina/silicon carbide composite and alumina/mullite composite was determined by abrasive wear tests. Microstructure of the samples was observed by transmission electron microscope (TEM). Morphologies of the worn and fracture surfaces were analyzed by scanning electron microscope (SEM). The influence of fracture mode and wear surface pullout on wear resistance was studied. The results are listed as follows, the main wear mechanisms of alumina and alumina/silicon carbide are fracture wear and plastic wear respectively, and as alumina/mullite composite is concerned, fracture wear and plastic wear mechanism exerted combined effect. Compared with that of alumina, wear resistance of alumina/silicon carbide compsosite and alumina/mullite composite is improved by 2--4 times. The primary source for the improvement is the reduction of area fraction of pullout induced by fracture mode transition.

通过磨粒磨损试验测定了氧化铝 陶瓷、氧化铝/碳化硅复合陶瓷和氧化铝/莫来石复合陶瓷的耐磨性. 利用透射电子显微镜(TEM)观察了样品的微观结构, 采用扫描电子显微镜(SEM)分析了样品的断口形貌和磨损表面的剥落情况. 研究了断裂方式对磨损表面剥落和耐磨性的影响. 结果表明: 氧化铝陶瓷的磨损主要由断裂磨损机制控制, 氧化铝/碳化硅复合陶瓷的磨损主要由塑性磨损机制控制, 氧化铝/莫来石复合陶瓷受这两种磨损机制共同作用. 相对于氧化铝陶瓷, 氧化铝/碳化硅复合陶瓷和氧化铝/莫来石复合陶瓷的耐磨性提高2～4倍, 这主 要是由于其断裂方式转变为以穿晶断裂为主, 减少了磨损面的脆性剥落.