Shahrooz Nafisi

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

Semi-Solid Metal (SSM) Technologies

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

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

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.

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.

Rheocasting: Low Pouring, SEED, and EMS Techniques

A novel method is introduced to investigate the macro-segregation in 356 Al-Si alloy. In this method, a portion of the remaining liquid is extracted during solidification of the alloy from the bottom orifice of a cylindrical sample. Different parts of the sample plus the extracted material are chemically analyzed and a good correlation between the chemical composition and the predicted values from binary Al-Si diagram was obtained. Comparing the chemical composition of the decanted alloy in the cast piece with those of the 356 standard range has shown that even with 15% of the liquid extraction, the composition of the alloy is still within the intended range.

Solidification and Alloy Distribution During SSM Processing

This chapter concentrates on understanding the mechanisms of nucleation and growth in three different rheocasting processes of low pouring, SEED, and electromagnetic stirring processes. The application of thermal analysis, parallel plate viscometry, and quantitative metallography verified the mechanisms responsible for microstructural evolution during the mentioned SSM processes.

Rheocasting-Melt Treatment

The process of semi-solid metal processing is also governed by solidification principles. However, the mechanisms controlling nucleation and growth of the primary phase and eutectic solidification are slightly different to conventional mechanism due to forced convection. The process of melt stirring influences alloy distribution and boundary layer characteristics. The mechanisms of nucleation and growth along with morphological evolution during melt stirring are discussed in this chapter.

Methodology of SSM Characterization

The process of melt treatment (grain refining and modification) is a routine practice for conventional Al–Si alloys casting. For SSM processes, it is worthwhile to see the effect of grain refiner and modification on the primary α-Al dendrites and eutectic silicon. This chapter provides a detailed analysis to verify the effect of melt treatment on the microstructure of as-cast SSM billets. The mechanism of grain refining and modification is examined through thermal analysis, rheological studies, and quantitative metallographic characterization for a range of grain refining master alloys and Sr-based modifiers in different rheocasting processes.

Applications of Thermal Analysis in Quality Control of Solidification Processes

The microstructure of the SSM alloy billets plays an important role during fabrication of finished engineering component and its performance in service. As a result, it is critically important to characterize the microstructure to ensure high-quality feed stock. This chapter provides a detailed account of the characterization techniques available to SSM researcher to confidently examine the quality of as-cast billets through thermal analysis, rheological characterization, and quantitative metallography.