Metals, Volume 6, Issue 5 (May 2016) – 28 articles

Extrudability of aluminum alloys of the 6xxx series is highly dependent on the microstructure of the homogenized billets. It is therefore very important to characterize quantitatively the state of homogenization of the as-cast billets. The quantification of the homogenization state was based on the measurement of specific microstructural indices, which describe the size and shape of the intermetallics and indicate the state of homogenization. The indices evaluated were the following: aspect ratio (AR), which is the ratio of the maximum to the minimum diameter of the particles, feret (F), which is the maximum caliper length, and circularity (C), which is a measure of how closely a particle resembles a circle in a 2D metallographic section. The method included extensive metallographic work and the measurement of a large number of particles, including a statistical analysis, in order to investigate the effect of homogenization time. Among the indices examined, the circularity index exhibited the most consistent variation with homogenization time. The lowest value of the circularity index coincided with the metallographic observation for necklace formation. Shorter homogenization times resulted in intermediate homogenization stages involving rounding of edges or particle pinching. The results indicated that the index-based quantification of the homogenization state could provide a credible method for the selection of homogenization process parameters towards enhanced extrudability. Full article

For the first time ever, a thickness dependence of the Lüders effect in an Al-based alloy is demonstrated. A three-dimensional digital image correlation method was used to gain insight into the Lüders band velocity and the Lüders strain. The results revealed that both the strain and velocity depend on the specimen thickness. The strain increases, whereas the velocity decreases, with decreasing specimen thickness. Moreover, the plot of the strain vs. the velocity concurs with the global deformation compatibility. Full article

In this study, thermal simulation experiments under different austenitization temperatures and different stress states were conducted. High-temperature laser scanning confocal microscopy (LSCM), thermal dilatometry, and scanning electron microscope (SEM) were used to quantitatively investigate the effects of the uniaxial compressive stress on bainitic transformation at 330 °C following different austenitization temperatures. The transformation plasticity was also analyzed. It was found that the promotion degree of stress on bainitic transformation increases with the austenitization temperature due to larger prior austenite grain size as well as stronger promoting effect of mechanical driving force on selected variant growth at higher austenitization temperatures. The grain size and the yield strength of prior austenite are other important factors which influence the promotion degree of stress on bainitic transformation, besides the mechanical driving force provided by the stress. Moreover, the transformation plasticity increases with the austenitization temperature. Full article

Current research has highlighted that magnesium and its alloys as biodegradable material are highly suitable for biomedical applications. The new material fully degrades into nontoxic elements and offers material properties matching those of human bone tissue. As biomedical implants are rather small and complex in shape, the metal injection molding (MIM) technique seems to be well suited for the near net shape mass production of such parts. Furthermore, MIM of Mg-alloys is of high interest in further technical fields. This study focusses on the performance of MIM-processing of magnesium alloy powders. It includes Mg-specific development of powder blending, feedstock preparation, injection molding, solvent and thermal debinding and final sintering. Even though Mg is a highly oxygen-affine material forming a stable oxide layer on each particle surface, the material can be sintered to nearly dense parts, providing mechanical properties matching those of as cast material. An ultimate tensile strength of 142 MPa, yield strength of 67 MPa, elastic modulus of 40 GPa and 8% elongation at fracture could be achieved using novel organic polymer binders for the feedstock preparation. Thus, first implant demonstrator parts could be successfully produced by the MIM technique. Full article

Mineralogical phases of steelmaking slags have significant influences on the carbonation of the slags. In this paper, the effects of temperature and reaction time on the conversion of calcium-related phases and the carbonation degree of a slag sample were studied. The experimental conditions were a liquid-to-solid ratio of 20 mL/g, a carbon dioxide flow rate of 1 L/min and a slag particle size of 38–75 μm. The results show that the optimum carbonation temperature and reaction time are 60 °C and 90 min, respectively, and calcite phase content is about 26.78% while the conversion rates of Ca₃Al₂O₆, CaSiO₃, Ca₂SiO₄ and free CaO are about 40%, 42.46%, 51% and 100%, respectively, and the carbon dioxide sequestration efficiency is about 170 g/kg slag. Full article

Rod samples of Mg₆₀Zn₃₅Ca₅ bulk metallic glass composites (BMGCs) dispersed with Ti particles have been successfully fabricated via injection casting. The glass forming ability (GFA) and the mechanical properties of these Mg-based BMGCs have been systematically investigated as a function of the volume fraction (V_f) of Ti particles. The results showed that the compressive ductility increased with V_f. The mechanical performance of these BMGCs, with up to 5.4% compressive failure strain and 1187 MPa fracture strength at room temperature, can be obtained for the Mg-based BMGCs with 50 vol % Ti particles, suggesting that these dispersed Ti particles can absorb the energy of the crack propagations and can induce branches of the primary shear band into multiple secondary shear bands. It follows that further propagation of the shear band is blocked, enhancing the overall plasticity. Full article

By modifying the accumulative roll-bonding (ARB) procedures, accumulative roll-bonding (ARB) processing up to 30 cycles (N) with a 50% thickness reduction per cycle (equivalent strain = 24) at room temperature was conducted on pure copper. The bonding condition, microhardness and electrical conductivity of the ARBed Cu were studied. Results showed that good bonding condition of the samples was achieved. As N increases, the microhardness of ARBed Cu increases, reaching ~2.9 times that of annealed Cu for N = 30. The electrical conductivity of ARBed Cu decreases slightly but with periodic fluctuations for N > 10, with a minimum of 90.4% IACS for N = 30. Our study indicated that ARB can be an effective way to produce high-hardness and high-conductivity pure copper better than or comparable to Cu alloys and Cu based composites as reported. Full article

In this paper a study is presented of the tensile fracture behavior of progressively-drawn pearlitic steels obtained from five different cold-drawing chains, including each drawing step from the initial hot-rolled bar (not cold-drawn at all) to the final commercial product (pre-stressing steel wire). To this end, samples of the different wires were tested up to fracture by means of standard tension tests, and later, all of the fracture surfaces were analyzed by scanning electron microscopy (SEM). Micro-fracture maps (MFMs) were assembled to characterize the different fractographic modes and to study their evolution with the level of cumulative plastic strain during cold drawing. Full article

The flow transport of a 420 × 320 × 90 mm beam blank continuous casting mold that used open-stream pouring combined with submerged refractory funnels was studied. By considering the dynamic similarity, geometric similarity, and air entrapment quantity similarity, a full-size water model was established. Meanwhile, the 3D mathematical models that included three phases were applied. Through the combination of the water model and the mathematical model, the distribution and morphology of the phases in the mold were investigated. The results indicate that bubbles existed in the molten steel due to entrapment and the flow pattern was different from that of the full protection-poured mold. Furthermore, the effects of funnel immersion depth and funnel diameter on the bubbles’ impact depth, funnel’s inside wall shear stress, and overall area of the air/steel interface were discussed. The results provide useful information for the industrial continuous casting process. Full article

A two-step strain-induced melt activation (TS-SIMA) process that omits the cold working step of the traditional strain-induced melt activation (SIMA) process is proposed for 6066 Al-Mg-Si alloy to obtain fine, globular, and uniform grains with a short-duration salt bath. The results show that increasing the salt bath temperature and duration leads to a high liquid phase fraction and a high degree of spheroidization. However, an excessive salt bath temperature leads to rapid grain growth and generates melting voids. The initial degree of dynamic recrystallization, which depends on the extrusion ratio, affects the globular grain size. With an increasing extrusion ratio, the dynamic recrystallization becomes more severe and the dynamic recrystallized grain size becomes smaller. It results in the globular grains becomes smaller. The major growth mechanism of globular grains is Ostwald ripening. Furthermore, high-temperature compressibility can be improved by the TS-SIMA process. After a 4 min salt bath at 620 °C, the high-temperature compression ratio become higher than that of a fully annealed alloy. The results show that the proposed TS-SIMA process has great potential. Full article

Consistent and high quality ramming paste products, installed according to optimized procedures, are required for improved operation and longer pot life. However, ramming paste used to be a hazardous product and needs special precautions for handling and application. A 100% eco-friendly cold ramming paste has been developed by Carbone Savoie and tested at Emirates Global Aluminium (EGA) sites. A test has also been developed by Carbone Savoie to follow-up, identify and quantify emissions during the baking of paste up to 1000 °C. Physico-chemical characteristics of various pastes are presented, together with their composition in polycyclic aromatic hydrocarbons (PAH) and volatile organic compounds (VOC), determined by an accredited laboratory and the results of emissions during paste baking. The results of pot operation at the EGA sites show no harmful impact on pot preheat, early operation, or regular operation performance. Pot performance data are given for comparison. The new paste offers a green and clean alternative to harsh chemicals typically associated with the industry. Full article

Nowadays, environmental regulation encourages carmakers to reduce the global vehicle weight. Steelmakers develop grades with high performance (Advanced High Strength Steels, AHSS) and fine steel sheet assemblies are used in car body structures, with an optimized thickness in each part. However, unusual fracture modes are sometimes observed during the mechanical tests of heterogeneous AHSS welds, made of dissimilar steel grades and sheet thicknesses. Weld fractures can occur with a strength lower than expected. This study aims at understanding these fracture mechanisms and focuses on two common steel grades joined by Resistance Spot Welding (RSW): DP600 (a dual phase steel) and Usibor^®1500 (a martensitic steel). The parameters affecting the failure modes and load bearing capacity are investigated during two common types of tests: the Cross Tension and Tensile Shear tests. The positive effects of heterogeneous welding with respect to the corresponding homogeneous configurations are discussed, as well as the consequences of a so-called Dome failure occurring at the weld nugget boundary. Full article

In the present work, metallic foams of Al, Mg and an Al-SiC nanocomposite (MMNC) have been fabricated using a new manufacturing technique by employing melt infiltration assisted with an electromagnetic force. The aim of this investigation was to study and to develop a reliable manufacturing technique consisting of different types of metallic foams. In this technique, an electromagnetic force was used to assist the infiltration of Al-SiC slurry and of pure liquid metal into a leachable pattern of NaCl, thus providing perfect cellular structures with micro-sized porosities. A high frequency induction coil unit equipped with a vacuum chamber and a hydraulic press was used to manufacture the foam materials. Microstructures of the produced foam materials were explored by using Field Emission Scanning Electron Microscopy (FESEM). The mechanical behavior of the manufactured foams was investigated by applying compression testing. The results indicate a high applicability of the new technique in producing metallic foams of pure metals and of a metal matrix nanocomposite . The produced foam materials displayed isotropic cellular structures with excellent compressive behaviors. Microstructure measurements indicate that the average pore size and strut thickness that can be achieved are in the ranges of 100–500 μm and 50–100 μm, respectively. The produced foam of the Al-SiC nanocomposite material provided the highest strength of 50 MPa prior to the densification stage, which equates to 25 times, and 10 times higher than the strength levels that were obtained by Al, and Mg foams, respectively. Full article

Effects of reflow time on the interfacial microstructure and shear strength of the SAC/FeNi-Cu connections were investigated. It was found that the amount of Cu₆Sn₅ within the solder did not have a noticeable increase after a long time period of reflowing, indicating that the electro-deposited FeNi layer blocked the Cu atoms effectively into the solder area during a long period under liquid-conditions. The ball shear test results showed that the SAC/FeNi-Cu joint had a comparable strength to the SAC/Cu joint after reflowing, and the strength drop after reflowing for 210 s was less than that of the SAC/Cu joint. Full article

Titanium alloys, which are important in aerospace application, offer different properties via changing alloys. As design complexity and service demands increase, dissimilar welding of the titanium alloys becomes a particular interest. Linear friction welding (LFW) is a relatively novel bond technique and has been successfully applied for joining titanium alloys. In this paper, dissimilar joints with Ti-6Al-4V and Ti-5Al-2Sn-2Zr-4Mo-4Cr alloys were produced by LFW process. Microstructure was studied via optical microscopy and scanning electron microscopy (SEM), while the chemical composition across the welded samples was identified by energy dispersive X-ray spectroscopy. Mechanical tests were performed on welded samples to study the joint mechanical properties and fracture characteristics. SEM was carried out on the fracture surface to reveal their fracture modes. A significant microstructural change with fine re-crystallization grains in the weld zone (WZ) and small recrystallized grains in the thermo-mechanically affected zone on the Ti-6Al-4V side was discovered in the dissimilar joint. A characteristic asymmetrical microhardness profile with a maximum in the WZ was observed. Tensile properties of the dissimilar joint were comparable to the base metals, but the impact toughness exhibited a lower value. Full article

The effects of basicity and MgO content on reduction behavior and separation of iron and slag during smelting vanadium titanomagnetite by electric furnace were investigated. The reduction behaviors affect the separation of iron and slag in the direct reduction-electric furnace process. The recovery rates of Fe, V, and Ti grades in iron were analyzed to determine the effects of basicity and MgO content on the reduction of iron oxides, vanadium oxides, and titanium oxides. The chemical compositions of vanadium-bearing iron and main phases of titanium slag were detected by XRF and XRD, respectively. The results show that the higher level of basicity is beneficial to the reduction ofiron oxides and vanadium oxides, and titanium content dropped in molten iron with the increasing basicity. As the content of MgO increased, the recovery rate of Fe increased slightly but the recovery rate of V increased considerably. The grades of Ti in molten iron were at a low level without significant change when MgO content was below 11%, but increased as MgO content increased to 12.75%. The optimum conditions for smelting vanadium titanomagnetite were about 11.38% content of MgO and quaternary basicity was about 1.10. The product, vanadium-bearing iron, can be applied in the converter steelmaking process, and titanium slag containing 50.34% TiO₂ can be used by the acid leaching method. Full article

High-entropy alloys (HEAs) are single-phase systems prepared from equimolar or near-equimolar concentrations of at least five principal elements. The combination of high mixing entropy, severe lattice distortion, sluggish diffusion and cocktail effect favours the formation of simple phases—usually a bcc or fcc matrix with minor inclusions of ordered binary intermetallics. HEAs have been proposed for applications in which high temperature stability (including mechanical and chemical stability under high temperature and high mechanical impact) is required. On the other hand, the major challenge to overcome for HEAs to become commercially attractive is the achievement of lightweight alloys of extreme hardness and low brittleness. The multicomponent AlCrCuScTi alloy was prepared and characterized using powder X-ray diffraction (PXRD), scanning-electron microscope (SEM) and atomic-force microscope equipped with scanning Kelvin probe (AFM/SKP) techniques. Results show that the formation of complex multicomponent ternary intermetallic compounds upon heating plays a key role in phase evolution. The formation and degradation of W-phase, Al₂Cu₃Sc, in the AlCrCuScTi alloy plays a crucial role in its properties and stability. Analysis of as-melted and annealed alloy suggests that the W-phase is favoured kinetically, but thermodynamically unstable. The disruption of the W-phase in the alloy matrix has a positive effect on hardness (890 HV), density (4.83 g·cm⁻³) and crack propagation. The hardness/density ratio obtained for this alloy shows a record value in comparison with ordinary heavy refractory HEAs. Full article

The oxidation kinetics of low valence titanium and iron in Ti-bearing blast furnace slag were investigated, the activation energies were calculated, which are 461.1 and 437.3 kJ/mol, respectively. The results illustrate that the oxidation process of Ti³⁺ in the slag is controlled by chemical reactions. However, the chemical reaction between oxygen and iron, between slag and gas, is the determining step of the iron oxidation process. The effects of the isothermal oxidation on the content of Fe₂O₃, Fe_M, FeO, and Fe_T in the slag are discussed. The Fe²⁺ and Ti³⁺ in the molten slag were oxidized at high temperatures. Oxygen affinity of the slag can be described using oxygen capacity. The oxygen capacity of Ti-bearing blast furnace slag was investigated during the dynamic oxidation process, the results indicates that the oxygen capacity of the slag decreased with increasing oxidation time during the dynamic oxidation process. Full article

The aim of this study was to develop a biocompatible coating for wound dressings, containing iron oxide nanoparticles functionalized with patchouli essential oil in order to obtain improved antimicrobial properties able to prevent biofilm development and consecutive associated infections. The bioactive coating was prepared by the co-precipitation of a precursor in an alkaline solution of patchouli oil. The prepared surface was characterized by XRD (X ray diffraction), TEM (transmission electron microscopy), SAED (selected area diffraction), SEM (scanning electron microscopy) and FT-IR (Fourier transform infrared spectroscopy). The bioevaluation of the obtained coating consisted in antimicrobial, as well as in vitro and in vivo biocompatibility and biodistribution assays. The obtained coating revealed a strong anti-biofilm activity maintained up to 72 h, as well as a low cytotoxicity on mammalian cells and a good biodistribution after intraperitoneal injection in mice. These results demonstrate the promising potential of the respective coatings for the management of wound infections and for the development of soft materials with improved resistance to microbial colonization. Full article

This article investigates the effect of low-level ionizing radiation, namely X-rays, on the micro structural characteristics, resistance, and corrosion resistance of TIG-welded joints of AISI 304 austenitic stainless steel made using AISI 316L filler rods. The welds were made in two different environments: natural atmospheric conditions and a closed chamber filled with inert argon gas. The influence of different doses of radiation on the resistance and corrosion characteristics of the welds is analyzed. Welded material from inert Ar gas chamber TIG showed better characteristics and lesser irradiation damage effects. Full article

In this research, polyethylene terephthalate (PET), as a high-density thermoplastic sheet, and Aluminum A5052, as a metal with seven distinct surface roughnesses, were joined by friction spot welding (FSW). The effect of A5052’s various surface states on the welding joining mechanism and mechanical properties were investigated. Friction spot welding was successfully applied for the dissimilar joining of PET thermoplastics and aluminum alloy A5052. During FSW, the PET near the joining interface softened, partially melted and adhered to the A5052 joining surface. The melted PET evaporated to form bubbles near the joining interface and cooled, forming hollows. The bubbles have two opposite effects: its presence at the joining interface prevent PET from contacting with A5052, while bubbles or hollows are crack origins that induce crack paths which degrade the joining strength. On the other hand, the bubbles’ flow pushed the softened PET into irregularities on the roughened surface to form mechanical interlocking, which significantly improved the strength. The tensile-shear failure load for an as-received surface (0.31 μ $\mathrm{m}$ R_a) specimen was about 0.4–0.8 kN while that for the treated surface (>0.31 μ $\mathrm{m}$ R_a) specimen was about 4.8–5.2 kN. Full article

In this study, we comparatively investigate the low cycle fatigue behavior of Alloy 617 (INCONEL 617) weldments by gas tungsten arc welding process at room temperature and 800 °C in the air to support the qualification in high temperature applications of the Next Generation-IV Nuclear Plant. Axial total-strain controlled tests have been performed with the magnitude of strain ranges with a constant strain ratio (R_ε = −1). The results of fatigue tests consistently show lower fatigue life with an increase in total strain range and temperature at all testing conditions. The reduction in fatigue life may result from the higher cyclic plastic strain accumulation and the material ductility at high temperature conditions. A constitutive behavior of high temperature by some cyclic hardening was observed. The occurrence of serrated yielding in the cyclic stress response was also observed, suggesting the influence of dynamic strain aging during high temperature. We evaluated a well-known life prediction model through the Coffin-Manson relationship. The results are well matched with the experimental data. In addition, low cycle fatigue cracking occurred in the weld metal region and initiated transgranularly at the free surface. Full article

For studying the influence of a bilateral slid rolling process (BSRP) on the surface integrity of a thin-walled aluminum alloy structure, and revealing the generation mechanism of residual stresses, a self-designed BSRP appliance was used to conduct rolling experiments. With the aid of a surface optical profiler, an X-ray stress analyzer, and a scanning electron microscope (SEM), the differences in surface integrity before and after BSRP were explored. The internal changing mechanism of physical as well as mechanical properties was probed. The results show that surface roughness (Ra) is reduced by 23.7%, microhardness is increased by 21.6%, and the depth of the hardening layer is about 100 μm. Serious plastic deformation was observed within the subsurface of the rolled region. The residual stress distributions along the depth of the rolling surface and milling surface were tested respectively. Residual stresses with deep and high amplitudes were generated via the BSRP. Based on the analysis of the microstructure, the generation mechanism of the residual stresses was probed. The residual stress of the rolling area consisted of two sections: microscopic stresses caused by local plastic deformation and macroscopic stresses caused by overall non-uniform deformation. Full article

This paper aims at studying the monotonic and cyclic plastic deformation behavior of DIN 34CrNiMo6 high strength steel. Monotonic and low-cycle fatigue tests are conducted in ambient air, at room temperature, using standard 8-mm diameter specimens. The former tests are carried out under position control with constant displacement rate. The latter are performed under fully-reversed strain-controlled conditions, using the single-step test method, with strain amplitudes lying between ±0.4% and ±2.0%. After the tests, the fracture surfaces are examined by scanning electron microscopy in order to characterize the surface morphologies and identify the main failure mechanisms. Regardless of the strain amplitude, a softening behavior was observed throughout the entire life. Total strain energy density, defined as the sum of both tensile elastic and plastic strain energies, was revealed to be an adequate fatigue damage parameter for short and long lives. Full article

Dissimilar diffusion bonds of TiAl alloy to AISI 310 stainless steel using Ni/Ti reactive multilayers were studied in this investigation. The Ni and Ti alternating layers were deposited by d.c. magnetron sputtering onto the base materials, with a bilayer thickness of 30 and 60 nm. Joining experiments were performed at 700 and 800 °C for 60 min under pressures of 50 and 10 MPa. The effectiveness of using Ni/Ti multilayers to improve the bonding process was assessed by microstructural characterization of the interface and by mechanical tests. Diffusion bonded joints were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED), high resolution TEM (HRTEM) and Fast Fourier transform (FFT). The bonding interfaces are thin (approximately 5 µm thick) with a layered microstructure. For all joints, the interface is mainly composed of equiaxed grains of NiTi and NiTi₂. The thickness and number of layers depends on the joining conditions and bilayer thickness of the multilayers. Mechanical characterization of the joints was performed by nanoindentation and shear tests. Young´s modulus distribution maps highlight the phase differences across the joint´s interface. The highest shear strength value is obtained for the joint produced at 800 °C for 60 min under a pressure of 10 MPa using Ni/Ti multilayers with 30 nm of bilayer thickness. Full article

This paper describes results of experimental research on the thin microhardened surface layer of a machined surface that occurs in materials using wire electrical discharge machining (WEDM) with brass wire electrode. The direct influence of microhardened surface layer on resulting machined surface quality of tool steel EN X210Cr12 (W.-Nr. 1.2080) was examined. The aim of the experiment was to contribute to the knowledge of mutual interactions between main WEDM technological parameters, the influence of these parameters on the total affected depth, and on the variation of microhardness of sub-surface layers of machined surface. Based on the microhardness experimental measurements, mathematical models were established by the Least Square Method (LSM) in order to simulate and predict final quality of machined surface after WEDM. Recommendations are given for setting the main technological parameters of the discharge process concerning minimization of total microhardened surface layer depth and microhardened surface layer homogeneity along the whole cross-section profile of the machined surface. Full article