Reza Ghomashchi

Fractional design of experiments applied to a wear simulation

Abstract A multidisciplinary approach to wear simulation to investigate rolling-sliding abrasion is described. Wear is a stochastic process where fatigue combines with abrasion, adhesion and corrosion. Statistical methods were found to be highly suitable for conceiving and analysing laboratory simulation of the wear process. A special procedure of so-called two-level complex design of experiments is described. By the way of an example, a fractional experimental design is presented showing a procedure for simulataneous evaluation of the influence of force, temperature, material and sliding on abrasion of rolling mill tool materials. A set of laboratory treatments was conducted via two-disc testing and single-scratch testing. The results, including analyses of the wear track via profilometry and metallography are described. Wear phenomena are discussed from statistical, mechanistic and microstructural viewpoints. The heterogeneous polycrystalline materials exhibit inherently stochastic attributes. The additional factors causing the dispersion in the measured wear rate were the technical characteristics of the laboratory devices. However, by virtue of the statistical design of the experiments and subsequent analyses, these variations were monitored, and the main effects and interactions, characterising the abrasive wear, were satisfactorily diagnosed.

SEMI-SOLID METAL PROCESSING ROUTES: AN OVERVIEW

Abstract Semi-solid metal (SSM) processing routes have attracted the attention of major as-cast auto parts producers due to their many technological and economical advantages. The current overview attempts to systematically classify the presently available SSM technologies and highlight the possible mechanisms involved in evolving the SSM structures. The paper is intended more for technologists than for pure solidification scientists. Les méthodes de traitement de métal demi-solide (SSM) ont attiré l’attention des principaux producteurs de pièces brutes de coulée pour l’automobile en raison de leurs nombreux avantages techniques et économiques. Le présent exposé tente de classifier systématiquement les techniques SSM disponibles actuellement et de mettre en lumière les mécanismes possibles impliqués dans le développement des structures SSM. Ce document vise plutôt les techniciens que les scientifiques pures de la solidification.

Semi-solid processing of aluminum alloys

An overall view of aluminum production and application is presented with the latest statistics. The challenges facing the aluminum industry and major aluminum producers worldwide are mentioned. Guidelines are given for future development of aluminum shaping with main emphasis on casting and foundry technology. Semi-solid metal casting is introduced as an alternative to reduce environmental effects of aluminum shape casting through reduction of energy consumption and generation of pollutants. Since its first commercial production in 1854, aluminum has proved to be one of the most versatile and useful materials discovered and extracted from the earth. It is the material of choice in a wide range of design and engineering applications because of its light weight, formability, corrosion resistance, and high specific strength; and is the world’s second most used metal after iron (steels). Moreover, it is one of the most readily recyclable materials in use for packaging, medical and electrical applications, and motor and automotive manufacturing. Nearly three-quarters of the aluminum ever produced in the world remains in use today because by its nature, it is endlessly recyclable. The aluminum industry is vital to the world economy with a production rate of 57.5 Mt in 2015 with China (31.2 Mt), Middle East (5.1 Mt), North America (4.5 Mt), Europe (4.4 Mt), CIS (3.9 Mt) and Rest of Asia (3.4 Mt) being the top six aluminum producing regions in the world [1]. As an example of the importance of aluminum to individual country’s economy, aluminum contributed to Australian economy with nearly A

Prediction of welding stresses in WIC test and its application in pipelines

4.4 billion worth of export in 2014 [2]. For Canada as the third producer of aluminum, exportation of aluminum represents more than 10% of the overall value of goods exported by Canada in 2013 [3]. The world production of aluminum since 1950 is given in Fig. 1.1 and the pie chart for 2015 production in Fig. 1.2 shows China producing more than half of the world’s aluminum [1]. Given its inherent properties and potential as a sustainable resource, new ways of using aluminum in manufacturing processes and manufactured products are currently being investigated worldwide. The roadmap on aluminum [4, 5] identifies specific areas where research is urgently needed to bring aluminum to its full potential. EU + EFTA + Bosnia and Montenegro

A model of hydrogen assisted cold cracking in weld metal

In the present study, the Welding Institute of Canada (WIC) restraint test was used to simulate the restraint conditions of full-scale girth welds on energy pipelines to ascertain the influence of welding process parameters on welding stresses. Finite element models are developed, and validated with neutron diffraction measurements, to evaluate the welding stresses for under-matched, matched and over-matched welds. The effects of heat input, wall thickness and variable restraint lengths of WIC sample are systematically investigated. As a practical outcome, this work can help in selection of the appropriate restraint length for WIC tests to simulate the specified stress conditions in the pipeline, and, ultimately, reduce the risk of Hydrogen Assisted Cold Cracking (HACC) in high strength low alloy. This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Evolution of primary α-Al particles during isothermal transformation of rheocast semi solid metal billets of A356 Al–Si alloy

Due to significant cost and productivity advantages, low heat inputs, high welding speeds, severe loading conditions and the use of cellulosic electrodes in the construction of oil and gas pipelines are unavoidable in Australia. Another significant cost reduction directly related to the tonnage of steel pipe dictates the wider use of higher grade steels, such as X70, X80 or X100. These current tendencies raise a serious concern regarding potential problems associated with weld metal hydrogen assisted cold cracking, HACC. Although there are industry standards and guidelines for the avoidance of hydrogen cracking in the heat affected zone, this is not the case for the weld metal, which is now more likely source of crack initiation in modern pipeline steels. The current paper develops a simplified mathematical model to predict the risk of hydrogen cracking in weld metal. A sensitivity study is conducted to evaluate the effect of various welding parameters and geometry, such as heat input, preheat and ambient temperatures and wall thickness on the risk of hydrogen cracking.Copyright

Semi-Solid Metal (SSM) Technologies

Abstract Semi solid metal (SSM) processing is a relatively new technology for metal forming, different from the conventional metal shaping technologies that use either solid or liquid metals as the starting material. Semi solid metal processing deals with semi solid slurries, in which non-dendritic solid particles are dispersed in a liquid matrix. The solid volume fraction could vary between 0·1–0·5 with apparent viscosity close to that of liquid state. The slurry flows easily under pressure and makes complicated shapes with high degree of die filling and integrity. There are different ways to prepare SSM slurries including the application of direct or indirect mechanical stirring, chemical treatments of the melt, and manipulation of pouring temperature. One of the important parameters controlling the mechanical and flow characteristics of SSM billets is the morphology of the primary solid phase, e.g. α-Al for Al–Si alloys. The morphological evolution of primary α-Al particles of SSM processed A356 Al–Si billets is studied with variant soaking times, 0–480 s, at 595°C, i.e. 0·33 fraction solid before the applied compression force. The effect of applied compression force of 33 kgf on the evolution of dendritic morphology was also investigated at the same temperature and within the same holding time range. The microstructure was characterised quantitatively and showed that spheroidisation and coarsening are active during the course of treatment with the application of compressive forces bringing about further refinement. Le traitement de métal à l’état semi-solide (SSM) est une technologie relativement nouvelle de formage des métaux, différente des technologies conventionnelles de façonnage des métaux qui utilisent des métaux soit à l’état solide ou liquide comme matériel de départ. Le traitement SSM traite des coulis à l’état semi-solide, dans lesquels des particules solides non-dendritiques sont dispersées dans une matrice liquide. La fraction volumique du solide peut varier entre 0·1 et 0·5, avec une viscosité apparente proche de celle de l’état liquide. Le coulis s’écoule facilement sous pression en des formes compliquées avec un haut degré de remplissage du moule et d’intégrité. Il existe différentes façons de préparer les coulis de SSM, incluant l’application d’agitation mécanique directe ou indirecte, les traitements chimiques du bain et la manipulation de la température de coulage. L’un des paramètres importants contrôlant les caractéristiques mécaniques et d’écoulement des billettes de SSM est la morphologie de la phase solide primaire, par exemple Al-α dans les alliages d’Al–Si. On a étudié l’évolution morphologique des particules primaires d’Al-α de billettes traitées en SSM d’Al–Si A356, avec des temps d’incubation variant de 0 à 480 s, à 595°C – c’est-à-dire fraction solide de 0·33 avant la force appliquée en compression. On a également examiné l’effet de la force de compression appliquée de 33 kgf sur l’évolution de la morphologie dendritique, à la même température et dans la même gamme de temps de rétention. On a caractérisé quantitativement la microstructure et l’on montre que la sphéroïdisation et le grossissement sont actifs tout au long du traitement, l’application de forces compressives amenant davantage d’affinement.

Application of SEM-EBSD for Measurement of Plastic Strain Fields Associated With Weld Metal Hydrogen Assisted Cold Cracking

The concept of semi-solid casting is discussed with main emphasis on rheocasting along with a brief account of the mechanisms responsible for the microstructural development during rheocasting. A state of art of the available SSM processes discussed to highlight the engineering features of SSM processes already developed as well as those still at the development stage. After a detailed description of rheo-routes, thixo-routes are also mentioned to provide a concise view of SSM processes available to aluminum casting and foundry industry.

Impact of Mg addition on solidification behaviour of Al–7%Si alloy

The requirement for more efficient use of materials for pipelines has lead to the application of high strength low alloy steels such as X70 and X80 in pipelines. As the strength of these alloys has increased so has the risk of hydrogen assisted cold cracking (HACC). In Australia to minimize construction time, the root runs of girth welds are produced by shielded metal arc welding using cellulosic electrodes without either pre or post heating. Well defined welding criteria have been developed and are incorporated into the weld procedures for the elimination of HACC in the heat affected zone but the risk of cracking to the weld metal is still of concern.It has been reported that plastic deformation occurs prior to the formation of hydrogen cracks in weld metal. Therefore the evaluation of plastic strains at the micro- and nano-scale and their relationship to the weld metal microstructure could be of great significance in assessing the susceptibility of welds to weld metal hydrogen assisted cold cracking (WMHACC).A method for analysing plastic strains on the micro- and nano-scales using electron backscattered diffraction (EBSD) has been developed. This technique is based on the degradation and rotation of diffraction patterns as a result of crystallographic lattice distortion resulting from plastic deformation. The analysis can be automated to produce an Image Quality (IQ) map in order to relate the spatial distribution of plastic deformation to microstructural features e.g. grains or cracks.The development and assessment of techniques using Scanning Electron Microscopy (SEM) and EBSD for the determination of local plastic strain distribution in E8010 weld metal used for the root pass of X70 pipeline girth welds is discussed.Copyright

The Impact of Partial Drainage on Chemical Composition of 356 Al-Si Alloy

Abstract The impact of Mg addition to Al7Si alloy is investigated using thermal and image analyses. It is shown that Mg expands α-Al solidification range and eutectic forms over a thermal range. For alloys containing less than 0·6%Mg, differential scanning calorimetry analysis and thermodynamic calculations are incapable of predicting the formation of Mg2Si phase during solidification. Furthermore, Mg addition leads to the formation of greater percentage of α-Al primary phase which is beneficial during semisolid processing of hypoeutectic Al–Si alloys.