Search

Abstract A new cold worked, penetrative mechanical reinforcement method was evaluated for its potential to enhance joining between 2024-T3 aluminum matrix and glass fiber reinforced polymer (GFRP) for aerospace and automotive applications. In this study, the aluminum substrate surface was modified using a new cold working process which formed hooks directly from the substrate material. This surface was then treated with grit blast and Sol-Gel surface treatment before it was co-cured to both side of a GFRP, forming a single lap joint for testing. This type of joints was compared to a baseline bonded joint without mechanical reinforcement using the same surface treatment. The joint strength and fatigue performance of these sets of samples were experimentally evaluated under quasi-static and fatigue loading conditions. The bonded joints with penetrative mechanical reinforcements withstood greater peak load and higher strain prior to failure, as compared to non-reinforced bonded joints. Fatigue testing on the other hand showed better performance of non-reinforced joints over the reinforced ones. The failure surfaces of both quasi-static samples and fatigue samples were evaluated using a scanning electron microscope to determine failure mode(s). It was determined that the stress concentration at the base of reinforcements could be the main underlying cause for earlier onset of fatigue failure of reinforced samples. [ABSTRACT FROM AUTHOR]

The dissimilar joints between 7A04 aluminum alloy rod and AZ31 magnesium alloy rod were produced by inertia friction welding. The effects of friction pressure on microstructure and mechanical properties of the joints were investigated. Results showed that intermetallic compounds (IMCs), mainly Al 12 Mg 17 and Al 3 Mg 2 , were formed at the interfaces. A large amount of microcracks were generated in IMCs interlayer. The thickness of IMCs layer decreased significantly with increasing friction pressure. The mechanical properties were assessed by tensile test and microhardness. The mechanical properties of joints largely lies on the characteristic of IMCs interlayers at the interface. The tensile strength of the joints increases remarkably with increasing friction pressure. The maximum tensile strength of 96 MPa was achieved under the friction pressure of 124 MPa. All the tensile specimens failed in quasi-cleavage fracture mode along the boundary between IMCs interlayer and Al base metal. [ABSTRACT FROM AUTHOR]

It has been shown in our previous effort in the development of an energy-based fatigue life prediction framework that, in order to obtain the fatigue toughness of a nonviscoplastic material at room temperature from the areas of hysteresis loops, a fatigue test need to be conducted at the ideal frequency to minimize the effect of nondamaging energy. For aluminum 6061-T6, the ideal frequency is 0.05 Hz. A fatigue test with such a low frequency requires extensive time to complete. Therefore, the present investigation focuses on modifying the energy-based framework in order to obtain the fatigue toughness from fatigue tests conducted at an arbitrary frequency higher than the ideal frequency. The fatigue toughness is calculated from the average strain range developed in a material during a fatigue test and the Ramberg–Osgood cyclic parameters. The measurement of average strain range by an extensometer associated with a nonviscoplastic test specimen at room temperature is independent of the test frequency. The cyclic parameters are obtained from the fatigue lives at two different stress ranges which are also independent of the test frequency at room temperature. Similar to the case of the previous framework, the modified framework is found to predict the room temperature fatigue life of aluminum 6061-T6 with a promising accuracy. [ABSTRACT FROM AUTHOR]

For this study, seamless square tubes of aluminum alloys EN AW-6060 and EN AW-6082 were extruded with axial variable wall thickness by applying an axial moveable stepped mandrel. The microstructures in thick-walled and thin-walled sections of these tubes were investigated and correlated to the extrusion conditions. The results for EN AW-6060 revealed fibrous grains at low ram velocity ( v ram = 0.8 mm/s) and thus low strain rate. In these cases, peripheral coarse grains were also observed on the tube surfaces. Applying a higher v ram = 3.3 mm/s lead to a fully recrystallized microstructure. For EN AW-6082 the fibrous microstructure was predominant. This was attributed to the Mn-content of this alloy, which acts as an inhibitor for recrystallization. Only at the highest values of strain, strain rate and temperature a recrystallized microstructure was observed for this alloy. EBSD analyzes of boundary misorientation angles indicate that geometric dynamic recrystallization seems to be the predominant mechanism at low strain rates. The facts that the amount of low angle boundaries significantly decreased as subgrains were removed and the amount of high angle grain boundaries is increased revealed that recrystallization occurred at higher strain rates and strains. Furthermore, the transition areas, where the wall thickness was gradually reduced were investigated. Due to increasing strain and thus increasing strain rate, thin-walled tube segments show lower grain size than thick-walled sections. It was also revealed that the PCG layer thickness remained about constant with increased strain, but since the tube wall thickness was reduced, the recrystallized fraction increased for higher strains. [ABSTRACT FROM AUTHOR]

The objective of this research was to develop a powder metallurgy (PM) counterpart to the wrought aluminum alloy 2618 utilizing press-and-sinter technology. Each starting blend was prepared from a strategic combination of prealloyed aluminum coupled with elemental and master alloy additions and was processed through uni-axial die compaction coupled with controlled atmosphere sintering. All of the PM alloys responded well to sintering with near full theoretical density realized. The most desirable PM product contained minor additions of tin and silicon. Whereas tin imparted enhanced densification, silicon promoted appreciable gains in hardness and tensile properties. It was also determined that the beneficial effects of silicon persevered after prolonged thermal exposure at 260 °C provided that a nominal concentration of 0.2 wt% was maintained. The final press-and-sinter PM product offered mechanical properties and thermal stability that were comparable to the wrought target. [ABSTRACT FROM AUTHOR]

Formation of linear polyenes -(CH=CH)- during thermal dehydration of thin layers (9-20 μm) of poly(vinyl alcohol) containing phosphotungstic-acid and aluminum-chloride catalysts was investigated. It was found that the concentration of long-chain ( n ≥ 8) polyenes in films containing phosphotungstic acid increased smoothly with increasing annealing time although the kinetics of the dehydration were independent of the film thickness. The polyene ( n ≥ 8) formation rate in films containing aluminum chloride dropped quickly with decreasing film thickness and increasing annealing time. As a result, long-chain polyenes practically did not form regardless of the annealing time for a film thickness of 11 μm. [ABSTRACT FROM AUTHOR]

Abstract: Constitutive equations for sheet metals are important input data for the numerical simulation of forming processes. Their identification usually comes from uniaxial tensile tests at several orientations to the rolling direction and from equibiaxial tests. To characterize the kinematic part of the work hardening, strain path reversals are needed and different mechanical tests have been developed, such as tension–compression and simple shear. The aim of this work is to investigate the influence of the database used for identification, by using either bending–unbending or simple shear for strain path reversal. This study is performed both on an aluminum alloy and a TRIP steel. The presented results show that, for a limited strain range, the experiments are consistent. [Copyright &y& Elsevier]

Abstract: The process of multi-pass offset tube neck-spinning is simulated by adopting MARC, the 3D elasto-plastic finite element software. 6061T1 aluminum alloy (annealed) is taken as investigating material. The distribution of stress and strain, the dimensional accuracy, such as thickness reduction, linearity, ellipticity and axial elongation in different spinning passes during multi-pass offset tube neck-spinning are simulated theoretically and studied experimentally. It shows that the distribution of strain and stress is non-axisymmetric; the equivalent stress distributes and varies along axial direction section by section, and reaches the maximum at the opening end of the spun workpiece. The thickness reduction at the opening end, and the ellipticity and axial elongation of the spun workpiece increase with increasing spinning passes; the linearity of the forward path spinning is significantly smaller than that of the backward path spinning. The simulation result of the thickness distribution of the workpiece conforms well to the experimental result with maximum deviation less than 10%. It indicates that the FEA model established in this paper is reasonable and reliable. The automobile exhaust pipe with offset tube end is produced successfully based on theoretical analysis and experimental research. [Copyright &y& Elsevier]

Abstract: The purpose of the present study is to propose a new technical method for arresting crack initiation at stop-drilled holes by drilling ancillary holes following the making of the stop-drilled holes. The main idea of the method is to reduce the stress concentration at the edges of stop-drilled holes. To confirm the effectiveness of the method, analyses were performed by using software for two-dimensional elastic problems based on the body-force method, and some experiments were carried out. The calculation results show that the existence of ancillary holes effectively reduced the stress concentration at the edges of the stop-drilled holes. A close distance between the stop-drilled hole and the ancillary holes resulted in lower stress concentration at the edge of the stop-drilled hole. Also, a considerable reduction of stress concentration was obtained by arranging for the diameter of the ancillary holes to be larger than that of the stop-drilled holes. Consecutively, the experimental results showed that the fatigue initiation life was in good agreement with the calculation results. [Copyright &y& Elsevier]

The LHC Accelerator Research Program (LARP) is currently developing 4 m long Nb3 Sn quadrupole magnets for a possible upgrade of the LHC Interaction Regions (IR). In order to provide a reliable test bed for the fabrication and test of long Nb,3Sn coils, LARP has started the development of the long racetrack magnet LRS01. The magnet is composed of two 3.6 m long racetrack coils contained in a support structure based on an aluminum shell pre-tensioned with water-pressurized bladders and interference keys. For the phase-one test of the assembly procedure and loading operation, the structure was pre-stressed at room temperature and cooled down to 77 K with instrumented, solid aluminum "dummy coils". Mechanical behavior and stress homogeneity were monitored with strain gauges mounted on the shell and the dummy coils. The dummy coils were replaced with reacted and impregnated Nb3 Sn coils in a second assembly procedure, followed by cool-down to 4.5 K and powered magnet test. This paper reports on the assembly and loading procedures of the support structure as well as the comparison between strain gauge data and 3-D model predictions. [ABSTRACT FROM AUTHOR]

Abstract: Chemical etching is employed as micromachining manufacturing process to produce micron-size components. The process applies a strong chemical etchant solution to remove unwanted part in the workpiece material. It is basically a corrosion-controlled process. Chemical etching process has a long history and accepted one of the important nontraditional machining processes during the last half century. The method is widely applied to machine geometrically complex parts from thin and flat of any material. It is also used to reduce weight of the workpiece materials. In this study, aluminium was machined by well-known chemical etchant, ferric chloride (FeCl3) at different etching temperature. The effects of selected chemical etching parameters on depth of etch and surface finish quality were investigated. It was observed that FeCl3 was very useful chemical etching for aluminium etching. [Copyright &y& Elsevier]

Abstract: Aluminum alloys 2014-T6, 2024-T3, 6061-T6, 7050-T7451, and 7075-T6 were thermally exposed at different times (1min to 20 days) and temperatures 177–482°C (350–900F). This study was conducted to simulate the effects of heat damage on aluminum alloys and to determine the correlations existing between the static mechanical and electrical conductivity properties. Results indicate that at the temperatures below 260°C (500F) all five alloys showed clear correlations between the mechanical and physical properties. [Copyright &y& Elsevier]

Abstract: The present study demonstrates different approaches towards MIC identification in three real cases of technological equipment failures. In the first case the failure of carbon steel heat exchanger as a result of tubes, lids, tube sheets, and connection pipes clogging was investigated. Chemical analysis of cooling water and precipitates, as well laboratory screening of deposits for bacteria, revealed that activity of iron-oxidizing bacteria present in cooling water led to heat exchanger blockage. The second case is related to MIC detection on floating roofs made of magnesium–aluminum alloy following a 3-weeks hydro-test. Corrosion tests carried out on the original and sterilized water used in hydro-test confirmed MIC process. In the third case the potential of MIC occurrence in engine cooling system made of cast aluminum alloy and filled with 20% ethylene glycol coolant solution was evaluated. The simulation tests allowed determining the real causes of the severe corrosion attack of examined system, including MIC high probability. [Copyright &y& Elsevier]

Abstract: Dry machining and high speed machining are increasingly attempted because of their impact on manufacturing cost. However, these processes generate dust that can be harmful. Environmental regulations require that manufacturers reduce manufacturing hazards, hence the need to develop environmentally conscious processes and cutting strategies that will help them to achieve that goal. This work investigates the turning of the 6061-T6 aluminium alloy, and 1018 and 4140 steels, using carbide cutting tools. The cutting tool geometry and the cutting speed are varied and their effect on dust formation and chip formation studied. The size of the dust particle investigated is 2.5μm and under (PM2.5). A new dust unit, which can be used as an ecological factor, is introduced to compare the dust emissivity of the tested materials. This dust unit is then related to the cutting conditions, and experimental models are developed. A correlation is established between the chip formation, the tool lead angle, the cutting speed, and the dust emission, in order to determine the conditions required for minimal dust emission. [Copyright &y& Elsevier]

Abstract: A kinetic study of dissolution reaction of Al can waste was conducted for the synthesis of aluminum isopropoxide (AIP). With the used Al can and isopropyl alcohol (IPA) as reactants, the reaction was examined at the condition of 3molIPA/mol Al of stoichiometric ratio, adding 10−3 molHgI2/mol Al for catalyst and no agitation at the reaction temperature ranging from 70 to 82°C. After 17h, the reaction gave a 75% yield. A two-stage dissolution mechanism was proposed in which the dissolution rate is determined first by a chemical reaction and then by ash layer diffusion. On the basis of the shrinking core model with the shape of flat plate, the first dissolution rate of Al can was controlled by chemical reaction. The concentration of isopropyl alcohol was added to the reaction at the stoichiometric ratio, then it was largely changed through the dissolution reaction. Therefore, since the conversion rate of isopropyl alcohol varies greatly depending on the reaction time, it was included as an integral term of the reaction time. By using the Arrhenius expression, the apparent activation energy of the first chemical reaction step was determined to be 92.4kJmol−1. In the second stage, the dissolution rate is controlled by diffusion control through the ash layer. The apparent activation energy of the second step was determined to be 174.9kJmol−1. [Copyright &y& Elsevier]

Abstract: The praseodymium-aluminium perovskite–praseodymium oxide, PrAlO3–Pr2O3, and praseodymium-aluminium perovskite–praseodymium hexaluminate, PrAlO3–PrAl11O18, eutectics have been recently obtained by the micro-pulling down method. The aim of this work was determination of the chemical composition and electronic structure examination of the above-mentioned eutectics. [Copyright &y& Elsevier]

Abstract: Severe plastic deformation (SPD) is an efficient approach for the production of bulk ultra-fine grained or nanostructured materials that involves plastic deformation to very high strain. The Equal Channel Angular Extrusion (ECAE) is a deformation process, which realizes the concept of SPD as such that the above-mentioned structures can be obtained. In this paper, the experimental research on multi-pass ECAE process of a widely used aluminum 6061 alloy is conducted and the mechanical properties after ECAE process are investigated. To study the effect of pre-extrusion heat treatment on the mechanical properties, different heat treatment scenarios are conducted to obtain un-aged and aged samples. Sixteen passes of ECAE process at room temperature are done without any rotation of the workpiece and the relationship of mechanical properties with number of extrusion passes was identified. In addition, mechanical properties including yield strength (YS) and the strain hardening exponent after the processing are investigated to determine the effect of the number of ECAE passes on the mechanical properties of the extruded samples. Results of the uniaxial tensile testing reveal that the YS of un-aged samples increased by ∼70% while aged samples exhibit an increase of ∼150% in YS after four passes of ECAE. There is a significant increase in the strain hardening exponent of the samples subjected to the different heat treatment configurations due to severe plastic deformation after multi-pass ECAE. The fracture surface of the tensile bars after uniaxial tensile testing was examined using scanning electron microscope (SEM) and the comparison of the fracture surfaces of the un-aged and aged specimens were presented. [Copyright &y& Elsevier]

Abstract: Both gravity casting and squeeze casting were carried out previously on an aluminium alloy (LM6) and a zinc alloy (ZA3) with different casting temperatures. Tensile, impact and density measurement were conducted. It was found that generally, samples taken from the bottom of the squeeze casting mould gave higher tensile strength, higher impact strength and higher density values. This study was carried out to determine the effect of solidification time on the mechanical properties of the castings. Two analytical methods were used: a steady-state heat flow model and Garcia''s virtual model. It was found that similar results were obtained with both analytical methods. Casting samples taken from the lower part of the squeeze casting mould were found to have a significantly shorter solidification time. For both types of alloys, it was found that generally the shorter the solidification time of the casting, the higher is its density, impact energy, yield strength and ultimate tensile strength (UTS). This study had therefore contributed to a better understanding of the mechanical properties obtained previously from different casting processes. [Copyright &y& Elsevier]

Abstract: Embossing and restoration are utilized to improve the mechanical properties of sheet metal. By subjecting the sheet to these techniques, the section modulus of the sheet metal is increased. Moreover, strain hardening is locally introduced on the sheet. With these strengthening methods, sheet metal of thinner gage can be utilized with remarkable improvement in mechanical properties, such as strength and rigidity. In this paper, embossing and restoration process are conducted to different aluminum alloy sheets. The effects of these techniques to the yield strength, tensile strength, total elongation and bending strength of the sheets are investigated. Also, the effects of bulge height during embossing and of forming condition on these mechanical properties of formed specimens are examined. The effectiveness of these forming techniques on strengthening the sheets is likewise discussed. [Copyright &y& Elsevier]