A journal published by Teksid Aluminum SrL twice a year and distributed world wide free of charge
Computers have now entered into the foundry engineering. Foundry mechanization and modernization are of considerable importance today when the foundry has evolved from an ancient art into a modern science and it is fully controlled and monitored by computers. Modernization is the only key to improve casting quality and productivity. From industrial point of view, they have been in use in the administrative areas of finance, accounting, personnel records, wage, salaries, and inventory control for a long period. Many foundry machine systems are computerized. Due to the entry of computers in foundries, fatigue and strain on the workers and staffs have been considerably reduced during working and work culture has improved tremendously. Improved work culture can lead to a sense of participation, involvement, and creativity. This review paper discusses on the role, prospects, and application of computers in foundries. Besides, an introduction on the computer aided foundry model design and computer aided foundry die design are presented precisely in this paper. It also discusses on the numerical simulation of casting solidification performed in foundries and a brief information about the computerized and automated foundry line have been provided in this technical paper. The applications of expert systems in foundries and various types of foundry software packages commonly used in the metal casting industries are explained in detail in this review paper.
Copyright (c) 2014 Metallurgical Science and Tecnology
Influence of injection parameters on the final surface quality of Al-Si-Cu die cast components
In foundry practice the occurrence of solidification defects limits the production and the performance of cast components. In high-pressure die casting (HPDC) the most common defects are shrinkage or gas porosities and bifilms. Thin sections, typical of HPDC components, are the most susceptible to casting defects, and these microstructural imperfections can be detrimental to both the mechanical and aesthetic properties. Even though laminations are not as harmful as internal defects, die cast components with this kind of superficial defects are always rejected by customers, thus requiring further machining operations. The aim of this study is to analyse the lamination defects that occur on the surface of some Al-Si-Cu cast covers produced by means of HPDC. In order to evaluate the influence of the different injection parameters on the final quality of the die casting products, melt temperature, plunger speed and upset pressure have been varied within a range of suitable values. The obtained castings have been studied by performing visual inspections and metallographic analyses by means of optical microscopy (OM), revealing the presence of many bifilms spread over the entire cross section of some cast parts. The presence of laminations, bifilms and cold shuts has been correlated to the considered processing conditions, proposing a new criterion parameter for the quantification of surface quality, called Lamination Ratio (LR).
Creep behaviour of Deep Cryogenic Treated AZ91 Magnesium alloy
The Deep Cryogenic Treatment (DCT) is known to have beneficial effects on mechanical behavior/properties of some alloys. It was also reported to be beneficial for the creep strength of Mg alloys. The present study is aimed at checking the effect of DCT on the high temperature behaviour of the Mg alloy AZ91 by means of comparative creep tests at 100 and 200°C carried out on high pressure die-cast specimens. In addition, the role played by initial microstructure was investigated by comparative creep tests on annealed and solution treated specimens. The mechanical tests were joined to optical and scanning electron microscopy observations on the creep specimens prior and after their high temperature exposure and to Differential Scanning Calorimetry analyses to investigate the thermal stability and the microstructural evolution of the alloy. The investigations results demonstrated that the effect of initial microstructure is by far more important for the creep properties of the Az91 alloy than the cryogenic treatment. DSC analyses revealed to be a useful tool to get information on the microstructural stability in view of the development of microstructure-based creep models
The use of Metal Treatment to control the quality of an Aluminium casting produced by the High Pressure Diecasting Process
The High Pressure Diecasting process is very attractive to the casting buyer, offering fast production rates coupled to optimised production costs. As castings become more complex and wall sections become heavier so the advantage of the very rapid cooling rate is reduced and casting defects more commonly seen in gravity diecasting and sand casting are now being experienced. The need to heat treat and weld castings also means that casting quality levels must be improved. A fresh approach to the treatment of the Aluminium melt is therefore required and this paper describes the design of a test piece and a test programme to examine the influence that metal treatment can have on casting quality. Simulation is used in the design of the test piece and various non-destructive tests are used to measure the quality of the Aluminium melt, prior to casting. Finally X-Ray, SEM and image analysis and mechanical testing are used to assess the quality of the resulting castings.
State-of-the-art characterization tools for Al foundry alloys
In this manuscript we review some characterization tools for Al foundry alloys. Castability is the ability of an alloy to be cast without formation of defects such as cracks, pores or misruns. Being able to measure, hence to control, these defects is fundamental and plays a critical role for the development of numerical models for castability. Also melt quality influences these defects formation. Alloy dependent phenomena that determine castability are, among others, fluidity and porosity. This manuscript focuses on the main characterization tools for measuring fluidity, porosity and melt quality.
Corrosion resistance of hot-dip Zn-6%Al-3%Mg alloy coated steel sheet used in automotive parts
For the purpose of applying hot-dip Zn-6%Al-3%Mg alloy coated steel sheet (“Zn-Al-Mg”) to automotive parts, we compared and investigated the corrosion resistance of Zn- Al-Mg and ordinary materials treated using a conventional rustproofing method (“post-Zn-coated material”) exposed to accelerated corrosion test environments. We also collected automotive parts made from Zn-Al-Mg from vehicles that had been driven for three to five years in Canada to examine corrosion resistance capabilities when exposed to actual vehicle environment conditions. We found that Zn-Al-Mg exhibited better corrosion resistance than post-Zn-coated material, even at portions where the steel substrate was exposed (along cut edges and in bent or spot-welded portions). Such Portions of the Zn-Al-Mg were observed as being covered by fine and dense Zn corrosion products containing Mg, which suppresses cathode reactions (dissolved oxygen reduction reactions). As a result, elution of the coating layer around such portions was suppressed and favorable corrosion resistance maintained. The flat and bent portions of automotive parts made of Zn-Al-Mg collected from actual vehicles were covered by fine and smooth corrosion products, with only little corrosion being observed. It was thus confirmed that Zn-Al-Mg also exhibits excellent corrosion resistance in an actual vehicle environment.
Synthesis of die-castable nano-particle reinforced aluminum matrix composite materials by in-situ gas-liquid reactions
Nano-particle reinforced aluminum matrix composites are attractive engineering materials for many automotive and aerospace applications because they exhibit numerous desirable mechanical and thermal properties, such as high specific strength, hardness, stiffness, and resistance to creep and thermal degradation. Unfortunately, making these materials is not easy and most of the methods that have been developed so far for their synthesis are either not robust, inefficient, or not cost effective. In this publication, we report on the synthesis of die-castable aluminum-aluminum nitride nano-composite materials by the reaction of a nitrogen-containing gas with molten aluminum-lithium alloy. Specifically, we report on the effect of (1) the lithium content of the alloy, (2) the composition of the reactive gas, and (3) the reaction time on (a) the amount, (b) the average size, and (c) the average cluster size of the aluminum nitride reinforcing particles; as well as (d) the hardness and (e) the thermal stability of the composite material.
Computed tomography as a promising solution for industrial quality control and inspection of castings
Recently X-ray Computed Tomography (CT) has successfully entered the field of industrial quality control, with interesting applications also for metal casting industry, including non-destructive testing and dimensional metrology. In particular, CT benefits of several advantages with respect to traditional dimensional measuring systems, as for example: simultaneous dimensional quality control and material quality control, non-destructive inspection of internal as well as external geometries, and reconstruction of complete and high-density point-clouds in relatively short time. Due to these advantages, CT is increasingly recognised as a very promising non-contact measuring technique and, therefore, several manufacturers and research centres are now investing in the further development of metrological CT systems and in widening their application in industry. This paper investigates accuracy and traceability of dimensional measurements carried out by state of-theart industrial CT systems, by examining selected results obtained from the “CT Audit” project, which is the first international interlaboratory comparison of CT systems for dimensional metrology. The project was organized by the Laboratory of Industrial and Geometrical Metrology, University of Padova, Italy, and was carried out in the period from September 2009 to June 2011, involving 15 CT systems, from research institutions and companies working actively on industrial CT metrology in Europe, America and Asia. The project was coordinated by Dr. Simone Carmignato
Improvement of wear and corrosion resistance of ferrous alloys by post-nitrocarburizing treatments
Improvement of wear and corrosion resistance of ferrous alloys by post-nitrocarburizing treatments R. Sola, R. Giovanardi, P. Veronesi, G. Poli
Mechanical characterization of aluminium alloys for high temperature applications Part 2: Al-Cu, Al-Mg alloys
Mechanical characterization of aluminium alloys for high temperature applications Part 2: Al-Cu, Al-Mg alloys R. Molina, P. Amalberto - Teksid Aluminum M. Rosso
Continuous galvanizing of martensitic and complex phase steels for automotive anti-intrusion applications
From the perspective of crashworthiness and passenger safety, martensitic and complex phase Ultra High Strength Steels (UHSS) are ideal candidates for automotive anti-intrusion components. However, these steels must be protected from corrosive environments in order to maintain the longterm integrity of the structures involved for which continuous galvanizing is a cost-effective solution. Several challenges have to be overcome in order to process the above steels in the continuous galvanizing line (CGL) while achieving the minimum target tensile strength of 1250 MPa. Steel chemical compositions should be selected in such a way that maintaining a suitable cooling rate produces martensite or bainite, and also provides a substrate surface with sufficient reactive wetting suitable for galvanizing. In the present study, steel chemistries were designed around relatively lean compositions based on carbon, manganese and silicon with additional hardenability being provided by molybdenum or chromium additions. Annealing cycles were determined based on the continuous cooling transformation behaviour of the steels. For both steel compositions the target tensile strength of 1250 MPa was achieved using austenitic annealing for 120s followed by cooling to room temperature at 50°C/s. The steels were successfully reactively wet by the Zn(Al,Fe) bath using a 95%N2-5%H2, -30°C dew point process atmosphere. From scanning electron microscopy, X-ray photoelectron spectroscopy and scanning Auger microscopy it was determined that oxides of manganese, silicon and chromium formed during annealing. However, these oxides did not have an adverse effect on coatability and both steels formed high quality, adherent coatings.
Validation of a combined CFD/FEM methodology for the evaluation of thermal load acting on aluminum alloy pistons through hardness measurements in internal combustion engines
This work presents the results of a multidisciplinary research project, carried out in close collaboration with Ducati Motor Holding S.p.A., for the development of an integrated methodology to design engine components in aluminum alloy under high thermal loads. The results refer to the study of an AA2618 (Al-Cu-Mg) alloy piston for high performance motorcycle engines. The piston has been selected as the pilot component for the development and validation of an advanced Fluid Dynamics (CFD) and Finite Element (FE) simulation methodology for the prediction of the inner thermal diffusion. The subsequent validation has been achieved through both the mechanical and microstructural characterization of the component. The methodology here presented consists of close interaction between fluiddynamics (CFD) simulations of the combustion process and Finite Element (FEM) simulations of the thermal diffusion inside the components. Combustion is the main engine heat source and is simulated by means of a threedimensional CFD code for reactive flows (FIRE v2008-AVL), with the use of advanced combustion (ECFM) and wall interaction models. The temperature map on the surfaces is based on the results of the iteration with FEM simulation of thermal diffusion. The FEM model used for the diffusion analysis receives the results of combustion analysis as input. Two different methods have been tested for the transfer of the CFD thermal load to the FEM models: a) imposition on the piston crown of a spatial distribution of heat flux averaged over the mean engine cycle; b) imposition on the piston crown of both heat flux coefficients and...
Mechanical characterization of aluminium alloys for high temperature applications Part1: Al-Si-Cu alloys
New challenges for the Aluminium alloys used for the production of castings for automotive engine components are coming from the evolution trend of Internal combustion engines towards higher specific power output. Cylinder heads, in particular, have to withstand higher operating temperatures and stress levels. The present study is aimed to evaluate the mechanical properties at high temperature of Al-Si-Cu aluminium alloys traditionally used for the production of cylinder head castings. The obtained results are very promising, especially for what concerns the modified alloys. In fact, the resistance of base Al-Si-Cu alloy is fairly good up to 150°C, but drops at 250°C, while some interesting improvements have been achieved by modifying the composition of the base alloy with the addition of Mn and Ni, resulting in an increase of strength and ductility at both room and high temperatures. Further studies related to High Cycle Fatigue and creep resistance at high temperature are under way. Moreover, the research will be continued also considering other alloys families, like Al-Mg and Al-Cu and the results will be discussed in a second part of the article. RI
Effect of post-welding heat treatments on mechanical properties of double lap FSW joints in high strength aluminium alloys
The present study focuses on the effect of postwelding heat treatments on mechanical properties of double-lap Friction Stir Welded (FSW) joints in 2024T3 and 7075T6 aluminium alloys. Heat treatments were performed at aging and solution temperatures. Micro-hardness profiles measured on transversal sections of postwelded heat treated joints reveal conditions (temperature and time) of hardness homogeneity at top, bottom and central nugget zone along the whole measured profile. When hardness homogeneity is reached, fracture occurs in the nugget. The double lap FSW joints after post-welding heat treatments at low temperatures (200° and 300°C) have tensile properties comparable with the as-FSW joint and fracture occurs in 7075T6 Base Material. At higher temperatures, fracture strain is almost 50% of joints deformed after heat treatment at lower temperature and failure occurs inside the stir zone. Polarized Optical Microscopy (POM) and Scanning Electron Microscopy (SEM) analysis reveal a progressive change in grain size and morphology in high temperature post-welding heat treated joints, leading to Abnormal Grain Growth in the stir zone.
Investigation on local mechanical properties in multiphase steels for designing local properties of constructional elements
The investigation deals processes leading to local strengthening in multiphase steels, being characterized by a good formability, continuous yielding, high strength and a strong bake hardening and aging effect. Dual phase (DP) and complex phase (CP) steels have been investigated to examine the effect of thermal and mechanical processing parameters on local properties. For this purpose, two methods have been used to achieve local strengthening, namely local deformation (LD) and local heat treatment (LHT). The local deformation by means of embossing with defined pre-strains leads to enhanced hardness and strengthening. A subsequent aging treatment results in a further increase in mechanical properties. Finally, a local laser heat treatment leads to an increase of hardness and strength and to local strengthening of the material. Local aging on the adjusted strength could be confirmed as well as the stability of the local strengthening. RIASSUNTO La ricerca riguarda i processi che portano al rafforzamento locale negli acciai a multifase, che sono caratterizzati da buona formabilità, snervamento continuo, elevata resistenza e da un effetto pronunciato di bake hardening e di invecchiamento. Sono stati studiati gli acciai “dual phase” (DP) e quelli a fase complessa (CP) per esaminare l’effetto delle variabili termiche e meccaniche di processo sulle proprietà locali. A questo scopo, sono stati usati due metodi per avere il rafforzamento locale, cioè deformazione locale (LD) e trattamento termico locale (LHT). La deformazione locale, effettuata mediante intaglio con predeformazione definita, porta all’aumento della
Influence of the solidification microstructure and porosity on the fatigue strength of Al-Si-Mg casting alloys
The fatigue behavior of Al-Si-Mg casting alloys is affected by the solidification microstructure and especially by defects such as gas pores, shrinkage pores and oxide films. This paper reports the microstructural characterization of a die cast engine head made of the A356 (G-AlSi7Mg0.3) alloy and the long-life fatigue strength determination using specimens extracted from the cast. The microstructural characterization was achieved by optical microscopy and digital image analysis to identify the different classes of solidification defects and to evaluate the correlation between local SDAS and the size and shape of the defects. Fatigue testing was performed under rotating bending and the stress amplitude vs cycles to failure dependence showed a large scatter. The reason for this is related to local stress concentration induced by the pores, which was analyzed by the finite element method, developing models of a material volume containing solidification pores characterized by 2D and 3D techniques (i.e. optical microscopy with image analysis and X-ray tomography, respectively).
Empirical models of mechanical behaviour of Al-Si-Mg cast alloys for high performance engine applications
Substructure characteristics in hot worked Al alloys are very important for modeling mechanical properties during hot forming, and also in the product. In contrast to simple grain shape in etched-optical microscopy (EOM), polarized optical microscopy (POM) significantly confirmed subgrain presence in better detail than x-ray diffraction (XRD). Transmission electron microscopy (TEM) revealed the dislocations forming subgrain boundaries (SGB) and dispersed between them; TEM in scanning mode (STEM) could provide microtextures substantiating XRD. Scanning electron microscopy with backscattered image (SEM-EBSI) exhibited substructures more accurately than POM but much less detailed than TEM. Finally, orientation-imaging microscopy (OIM) provided microstructures as in SEM-EBSI and also detailed misorientations; however, omission of very-low angle SGB seen in TEM gave rise to estimates of larger subgrain sizes and misorientations. The field of view is very limited in TEM, but fairly similar in POM, SEM-EBSI and OIM although higher magnifications are possible in the last two. The various techniques are also affected differently by substructure scale (temperature, strain and rate) and composition that also influence specimen preparation. Examination by several techniques is best assurance of correct interpretation of microstructural characteristics.
The main limitation of cast Al-Si-Mg alloys is the considerable influence of the solidification and heat treatment conditions on the final microstructure and consequently on the mechanical properties, that can thus widely vary in the same cast component. In this work we perform a deep microstructural and mechanical characterisation on specimens extracted from some A356 T6 gravity die cast cylinder heads. The aim of the work is to develop empirical models to successfully predict the local tensile properties of the casting from the main microstructural parameters and alloy hardness. As the former we considered and measured secondary dendrite arm spacing, shape and size of the eutectic silicon, grain size and percentage area of defects. The latter instead primarily depends on the heat treatment conditions. On the base of these data we propose a set of simple equations to predict the ultimate tensile strength and the proof strength with a mean error of 2% and the elongation to failure with a mean error of 20%. The equations allow the designer to know the local tensile behaviour without any tensile tests. Moreover, in a coengineered design approach, the equations can link the post-processing results of the casting simulation software to the preprocessing phase of the structural software. This leads to less bench tests and to a great reduction of validation time of a new product.
Constitutive and stochastic models to predict the effect of casting defects on the mechanical properties of High Pressure Die Cast AlSi9Cu3(Fe) alloys
The effect of casting defects on mechanical properties of a high-pressure die-cast AlSi9Cu3(Fe) alloy is reported. A series of Ushaped structural components are cast using a combination of injection parameters and pouring temperatures in order to generate different types and amount of casting defects throughout the casting. It has been found that castings contain defects, primarily pores and oxides, and that the presence and distribution of these defects are highly sensitive to the process conditions. Moreover, significant variations of the defect distribution have, however, been found in castings produced under the same conditions, indicating the stochastic nature of defects in die castings. The tensile properties are affected by the amount and distribution of defects and are determined by the defect area fraction. The influence of casting defects on mechanical properties are investigated through a theoretical verification based on constitutive and stochastic models. The analytical approach, based on the Ghosh constitutive model of tension instability, correctly indicates the trends of the experimental results, while the Weibull statistics evidences how the scale parameter and the Weibull modulus are strongly affected by the casting conditions. An integrated stochastic-analytical approach is then proposed and it appears to be applicable to describe the tensile properties in terms of fractographic defects and cumulative failure probability Pi.
A comparison between asymmetric rolling and accumulative roll bonding as means to refine the grain structure of an Al-Mg-Si alloy
The possibility of refining the grain structure of a commercial Al-Mg-Si alloy was evaluated using asymmetric rolling (ASR) and accumulative roll bonding (ARB) in the severe plastic deformation (SPD) regime. Bars of annealed alloy having a thickness of 10 mm were asymmetrically rolled down to a thickness of 0.23 mm with a laboratory rolling mill featuring the possibility of independently modifying the rotational speed of its two rolls. The effect of the rolling temperature was investigated by tests in the range 150-250°C. A parallel campaign was also conducted to investigate the effects of warm accumulative roll bonding of the same alloy and in the same temperature range. These tests were carried out on annealed samples of 1 mm thickness. The experimental characterization (both mechanical and m i c ro s t ructural) demonstrated that asymmetric rolling and accumulative roll bonding can readily promote the achievement of ultrafine grained structures in Al-Mg-Si alloys.
Mechanisms in creep and hot working to high strain; microstructural evidence, inconsistencies.
The dislocation mechanisms of dynamic recovery (DRV) in metals of high stacking fault energy (SFE) give rise to steady-state straining dependent on temperature and strain rate due to development of constancy in the spacings of subgrain boundaries (wS, SGB) and of the dislocations within both the SGB and the subgrains. When the grains are large compared to subgrains, the interactions of grain boundaries with SGB are limited to s e rration formation but when one-grain dimension is reduced to about twice the SGB spacing, the interactions begin to define a minimum grain dimension. However, the cellular size defined by the mixture of SGB and GB remains constant at wS along with the stress. In metals of low SFE, the above is seldom attained since dynamic recrystallization (DRX) intervenes to provide new grains more than twice the subgrain size. On a larger scale, transition boundaries between deformation bands lying between diff e rently slipping and rotating bands, become permanent and rapidly rise in angle and take on GB behavior in both DRV (serrations) and in DRX (nucleation sites). The evidence became more precise as techniques advanced through polarized optical, scanning and transmission electron and orientation imaging microscopies; however, deficiencies in each technique often created confusions that were resolved only through detailed comparison of the evidence.
Porosity reduction possibilities in commercial Aluminium A380 and Magnesium AM60 alloy components using the RheoMetalTM process
A commercial component was produced from both aluminium A380 (EN AC 46000) and magnesium AM60 alloys by high pressure die casting (HPDC) and rheocasting using the RheoMetal process. This process, which is based on the Rapid Slurry Forming (RSF) technology, is capable of producing large amounts of metal slurries in short times. The aim of this paper is to investigate the possibility to reduce porosity, and the related effects on the tensile properties obtained in RSF rheocast components. Significantly reduced pore content was obtained in the RSF rheocast A380 and AM60 alloy components, as compared to the HPDC components. This was confirmed by Xray analysis, microstructure analysis and on polished component sections. The turbulent filling behaviour in HPDC produces severe amounts of entrained gas type porosity. It was also found that gas pores often were connected to shrinkage type pores.
Microstructure evolution and creep behaviour of a new intermetallic alloy
The preliminary results of microstructural characterization and creep behaviour of an innovative TiAl 8% atomic Nb alloy are exposed in this paper. Two different batches of this material, with same nominal chemical composition, but produced through different solidification processes and heat treatments, have been studied. The production processes generated different ? + ?2 microstructures in the two batches, both analyzed through X ray diffractometry (XRD) and transmission electron microscopy (TEM). Constant load creep tests have been performed on both batches at the same temperatures (700?C and 850?C) and loads in order to compare the creep behaviours. XRD and TEM analyses have been carried out after creep tests in order to determine microstructural evolution of the materials and to establish correlation with creep behaviours.
Correlation between microstructure and mechanical properties of Al-Si diecast engine blocks
In spite of weight reduction of passenger car, the cylinder block is the heaviest component among many automotive engine parts and plays a key role in fuel efficiency and the drivability of vehicles. In hypoeutectic aluminium alloys, the final mechanical properties are strictly connected to microstructural features such as the distribution, the morphology and dimensions of primary ?-Al phase and eutectic Si particles, as well as, type of iron-bearings and defects. The microstructure, in turn, depends on filling process and solidification dynamic. In this work, a HPDC 4-cylinders-inline cylinder block was exhaustively analysed and mechanical properties were correlated to microstructural features. Mechanical properties are affected by microstructure. The best values of UTS and elongation to fracture are obtained for low secondary dendrite arm spacing (SDAS) values and small and more compact eutectic Si particles. If the combined effect of ?-Al phase and eutectic Si particles is taken into account, a linear correlation between UTS and product of SDAS, equivalent diameter and aspect ratio of Si particles is observed, while the elongation to fracture shows an exponential trend, suggesting an high sensitivity on microstructural variation.
Extrusion of aluminium hollow pipes:seam weld quality assessment via numerical simulation
The continuous extrusion of an aluminium alloy for hollow tubes production was investigated by numerical simulations. A variety of model runs were carried out exploring different combinations of die geometries and extrusion speeds. The primary objective of this work was to compare different criteria for evaluating the quality of longitudinal seam welds. The results of the numerical experiments show that the currently used quality indices, based on the integration of some characteristic variables across the welding surface are significantly affected by the extension of the dead flow zones. As a result, they do not behave coherently with respect to changes in shapes of the mandrel legs. The use of a novel Lagrangian approach in the estimation of the quality indices - based on the integration of the variables along the actual welding paths - leads to a more consistent behavior of the parameters with respect to both the extrusion velocity and the front leg shape. In this study we also show that the Lagrangian parameters can be applied to get a deeper insight into the quality of the extruded products, like the seam weld quality along the tube thickness. Further research is needed to investigate the relation between the Lagrangian quality indices and the microstructure of the material.
Mechanical and microstructural characterisation of A356 castings realised with full and empty cores
The use of full cores, for producing automotive components by means of the permanent mould casting technique, allows good castings with a low level of defects to be obtained. Nevertheless, an extra phase of the production cycle is necessary to have an optimal emptying of the internal cavities of the castings, with an increase in costs. This scenario motivated the present research, in particular to study the effect of replacing full cores with empty cores. The component analysed is one of the three parts of a motorcycle frame, realised in aluminum alloy A356 by permanent mould casting and T6 heat-treated. Several castings have been produced with both full and empty cores; tensile strength tests have been performed on samples drawn from four different zones, in order to compare the mechanical and microstructural properties of the castings realised with the two different kinds of core. A slight decrease in elongation at fracture has been verified in the samples drawn from the castings realised with empty cores, but yield strength and ultimate tensile strength are well comparable. A finer microstructure always corresponds to higher mechanical properties; an inverse correlation between secondary dendrite arm spacing and ultimate tensile strength has been found. The effect of secondary phases, porosities and morphology and distribution of eutectic silicon particles has been considered. The Japanese Taikai methodology has been improved in order to compare the current production cycle with the one optimised by the use of empty cores. Cost, weight and timecycle reductions in the production of the component, due to the elimination of the extra phase using empty cores, have been evaluated
The influence of Fe and Mn content and cooling rate on the microstructure and mechanical properties of A380-die casting alloys
In the present investigation, the microstructure and tensile properties of aluminium die-cast alloys, based on A380, are studied in details as a function of the iron and manganese content and solidification rate. One set of experiments was designed to examine the ?solely? effect of Fe content, which varied from 0.1 up to 1.6 wt % and another set with manganese additions, Mn:Fe ~ 1:2. Three solidification rates corresponding to ~ 10, 25 and 60 ?m in secondary dendrite arm spacing, SDAS, respectively were employed by using the unique gradient solidification technique. Microstructure analysis reveals that at relatively high cooling rates and iron levels, the iron-rich precipitates are suppressed to some extent and the strength is maintained at high levels, but the ductility is gradually decreased. The amount of iron-rich intermetallics does not appear to influence the size and area fraction of porosity and consequently the result suggests that tensile properties have not been adversely affected by porosity level. These results offer additional insight into commonly discussed microstructure features and their role in the determination of the quality and soundness of Al-Si cast alloys.
On the quality of A354 ingots and its impact on cast product
A study in an automotive casting plant was targeted to address the problem of high rejection rate of a cylinder head casting made from an A354 alloy. Ingots of an A354 alloy from three different suppliers, A, B and C, were analyzed by the reduced pressure test (RPT) and the pressure filtration (PREFIL) test, individually as well as in combination. Hydrogen measurements during casting trials was carried out with an ALSPEK H? analyzer. The results have shown a good agreement with the scrap rate data of the final cast product, and the problem of higher scrap rate was significantly reduced when the ingots of an A354 alloy with the highest oxide content from supplier C were replaced. In order to study the influence of transfer and de-gassing on the melt quality, reduced pressure tests were also conducted along the production line. The effect of melt holding time on the quality of the cast product is also presented. The results from these trials shows that the bifilm index data from the RPT has a potential to be used in an industrial environment for routine melt quality control as the cause of high scrap was successfully identified with this technique.
Theoretical and experimental study on ultrasonic dispersion of nanoparticles for strengthening cast Aluminum Alloy A356
Aluminum alloy A356 is of significance for numerous applications. The mechanical properties of A356 would be enhanced considerably if reinforced by thermodynamically- stable nanoparticles. However, it is very challenging to disperse nanoparticles uniformly in A356 melts for casting A356 nanocomposites. In this study, ultrasonic cavitation effect was proposed to disperse SiC nanoparticles in A356 melts before casting. The novel method was theoretically studied and then experimented. With only 1.0wt.% nano-sized SiC reinforcement (about 30nm), the ultimate tensile strength and yield strength of the aluminum alloy A356 were enhanced significantly while the ductility was retained. The study on micro/nano structures of the nanocomposites validates that a uniform distribution and effective dispersion of nanoparticles in A356 matrix were achieved. Moreover, a good bonding between the SiC nanoparticles and the Al matrix was obtained. This study paves a way for high volume solidification processing of metal matrix nanocomposites for industrial applications.
Effect of anisotropy on Fatigue properties of AA2198 Al-Li plates joined by Friction Stir Welding
Al-Li alloys are characterized by a strong anisotropy in mechanical and microstructural properties with respect to the rolling direction. In the present paper sheets, 4 mm thick, of AA2198 Al-Li alloy were joined via Friction Stir Welding (FSW) by employing a rotating speed of 1000 RPM and a welding speed of 80 mm/min, in parallel and orthogonal direction with respect to the rolling one. The joint mechanical properties were evaluated by means of tensile tests at room temperature. In addition, fatigue tests were performed by using a resonant electro-mechanical testing machine under constant amplitude control up to 250 Hz sinusoidal loading. The fatigue tests were conducted in axial control mode with R=?min/?max=0.33, for all the welding and rotating speeds conditions. The damage behavior was studied by applying thermoelastic stress analysis (TSA) to the crack formation and propagation of friction stir welded sheets under cyclic fatigue tests. The fatigue crack propagation experiments were performed on single edge notched specimens. Fatigue tests were carried out up to failure in tension- tension with load ratio R=0.33. The TSA measurement system allowed crack evolution to be observed in real-time during fatigue cycles and stress fields to be derived on the specimens from the temperature variation. The thermoelastic data were used to measure the principal stresses and principal strains on the specimens surface and the crack growth rate during tests. All the results were validated by employing finite element analysis performed with ABAQUS software. SEM observations of the fractured surfaces were done to characterize the weld performances.