During dendritic solidification of castings and ingots, a number of processes take place simultaneously within the semisolid region. These include crystallization, solute redistribution, ripening, interdendritic fluid flow, and solid movement. The dendritic structure which forms is greatly affected by convection during the early stages of solidification. In the limit of vigorous convection and slow cooling, grains become spheroidal. Alloys with this microstructure possess rheological properties in the semisolid state which are quite different from those of dendritic alloys. They behave thixotropically, and viscosity can be varied over a wide range, depending on processing conditions. The metal structure and its rheological properties are retained after solidification and partial remelting. The semisolid alloys can be formed in new ways, broadly termed «semisolid metal (SSM) forming processes». Some of these are now employed commercially to produce metal components and are also used to produce metal-matrix composites

Behavior of metal alloys in the semisolid state

This chapter gives a comprehensive account of the materials used in manufacturing vehicles. In the first section it explains the properties and characteristics that a suitable material should have to be accepted in automotive production. In later sections it reviews the history of development of the materials in automotive from the most traditional to the most recent ones. In the class of the metallic materials, steel, aluminium and magnesium and the most recent alloys of these used in the automotive are explained. Some of the properties, manufacturing and joining processes for these metals are described. The advantages and problems of using each of these materials are also reported. The potential application of these materials in different parts of a vehicle is identified. The other class of materials considered is composites and plastics with synthetic or natural fibre as reinforcement. Whilst the synthetic fibres are more traditional type of composites used, the natural fibre composites hold a relatively new place with substantial potential for growth due to the growing environmental concerns. With regard to the composite the cost is one of the most important barriers in use of these materials. Therefore a cost analysis is presented. Also the second barrier is a suitable manufacturing process for producing complex automotive parts. A review of the manufacturing process therefore is also offered for the composites with both synthetic and natural fibres. s

/pdf/materials-in-automotive-application-state-of-the-art-and-j044sgp1bz.pdf

Materials in Automotive Application, State of the Art and Prospects

Semi-solid processing of novel MMCs based on hypereutectic aluminium-silicon alloys

In prior work, we showed that eutectic Sn-Pb solder joints exhibit superplastic behavior after rapid solidification. Further examples of superplasticity in nominally air-cooled solder joints are reported in this study of three low-melting point alloys: 40In-40Sn-20Pb (wt. %), eutectic 52In-48Sn, and 43Sn-43Pb-14Bi, which were creep-tested in shear at 20°, 65°, and 90° C. The test results indicate that above 65° C, the indium-containing solders have stress exponents between 2.4 to 2.9, a possible overall shear strains of 500%, and an absence of primary creep; at 90° C, 43Sn-43Pb-14Bi solder has a stress exponent close to 2.3. Optical microstructures of the three solders are presented; they help to explain the superplastic behavior.

Superplastic creep of low melting point solder joints

The working principle and the peculiarities of new electromagnetic rheocasters, which are based on the use of rotating permanent magnets and which allow the production of intense stirring in solidifying semisolid alloy slurries, are described. Local measurement techniques are applied to the study of the evolution of the electromagnetic, hydrodynamic, and thermal phenomena with time inside vigorously agitated melt-solid mixtures. Satisfactory performances concerning the microstructure of solidified aluminum thixotropic slurries (homogeneity, crystal shape, grain size, and fraction of primary solid) were obtained.

Elaboration of semisolid alloys by means of new electromagnetic rheocasting processes

Technique de rheocoulee sous vide dans laquelle un alliage en cours de solidification est violemment agite. Application a des alliages a base d'Al contenant de 15 a 50% en poids de Pb

Production of Al–Pb Alloys by Rheocasting

Etude de la vitesse de refroidissement et de rotation sur la structure des alliages. Caracterisation par microscopie optique

Improvement of Microstructure in Hypereutectic Al–Si Alloys by Rheocasting

Technique dans laquelle des alliages Al-Cu contenant 10, 24 ou 30% en poids de Cu sont brasses sous vide par un agitateur a grande vitesse de rotation au cours de leur refroidissement, lorsqu'ils sont a l'etat de melange liquide-solide. Resultats

Stirring conditions and grain refinement in Al-Cu alloys by rheocasting

Etude microstructurale des alliages obtenus par la technique de la rheocoulee. Description des caracteristiques mecaniques de ces alliages

Modification of Hypoeutectic Al–Cu, Al–Si and Al–Ni Alloys by Rheocasting

An easy method and apparatus to eliminate casting defects from composite materials of hypereutectic Al-Si alloys and improve their properties. The product composite materials with primary silicon crystals of several microns have fine homogeneous microstructures and mechanical properties comparable to similar materials produced by the conventional powder metallurgy technology. Highly wear-resistant composite materials, in which the hypereutectic Al-Si alloy and strengthening material are homogeneously mixed, can be obtained with ease. The hypereutectic Al-Si alloy and strengthening material are homogeneously mixed by stirring blades rotated at low speed. The obtained molten composite alloy rotated at high speed about a horizontal shaft in a heat-resistant vessel. The rotor rotating and stirring at high speed spatters the molten composite alloy material to break up the crystallizing out primary silicon crystals. The rotor stirs the spattered semi-solid composite alloy material received by the heat-resistant vessel. A resulting semi-solid mass having a fine-grained homogeneous microstructure is recovered as the final product.

Satoshi Ishizuka

Papers

Production of Al–Pb Alloys by Rheocasting

Improvement of Microstructure in Hypereutectic Al–Si Alloys by Rheocasting

Stirring conditions and grain refinement in Al-Cu alloys by rheocasting

Modification of Hypoeutectic Al–Cu, Al–Si and Al–Ni Alloys by Rheocasting

Method for making hypereutetic Al-Si alloy composite materials