In some types of surgical implants, such as bone screws and plates, Grade 2 Ti is seriously considered as a replacement for the Ti-6Al-4V alloy. Advantages are lower cost and the absence of Al and V, which have been identified as potentially harmful to human health. The present paper shows that the lower strength of the commercially pure metal can be enhanced by Severe Plastic Deformation followed by conventional cold rolling, so as to reach a strength level higher than the technical requirements applicable to the alloy. This was ascertained by tensile and Vickers hardness tests from which it was concluded that the best combination of properties are obtained by submitting the metal to Equal Channel Angular Pressing (four passes at 300 °C) followed by a 70% thickness reduction by cold rolling. Although the present results are valid for the material only, and not for the product considered, that is, bone screws, it appears that this solution is a step towards the replacement of the Ti6-4 alloy by Grade 2 Ti, at least for some types of metallic medical implants.

O processo de conformação de ligas no estado semi-sólido (ESS) é uma tecnologia que, devido às vantagens, é uma realidade na indústria automobilística em especial para ligas de Al-Si. Um dos aspectos mais importante, nesse processo, é o comportamento reológico dessas ligas, pois, tal comportamento afeta diretamente as condições de fluxo e, também, as propriedades mecânicas finais das peças tixoconformadas. Uma maneira empírica para avaliar esse parâmetro é através do teste de fluidez. O objetivo do presente trabalho foi estudar a influência do tempo de espera sobre a fluidez da liga A356, no estado semi-sólido (ESS). Amostras foram semifundidas até uma temperatura de 590ºC, processo este seguido de tempos de espera de 10min e 30min. A liga refundida foi injetada em uma matriz com um longo canal contínuo. Os resultados obtidos foram discutidos, tendo, como base, teorias preexistentes para sistemas de coexistência sólido/líquido. Parâmetros microestruturais foram medidos, com o intuito de explicar os fenômenos observados. O grau de fluidez da liga A356 sofre intensa influência do tempo de espera no ESS.

Semi-solid state forming process (SS) is a technology that, due its benefits, is a reality for automotive industry applications, especially for aluminum silicon alloys. In this forming process, one of the most important aspects is alloy rheological behavior because it directly affects the flux condition and mechanical properties of tixoformed parts. An empiric way for measuring this parameter is the fluidity test. The aim of this work was to study the influence of waiting time on the fluidity of an A356 alloy in a semi-solid state. Samples were heated until partial melting at 590ºC, followed by waiting times of 10min and 30min. The alloy was injected into a long and continuous channel. The results obtained were discussed using pre-existent theories for semi-solid state systems with coexisting solid and liquid phases. Some microstructural parameters were measured to explain theobserved phenomena. The degree of fluidity of A356 alloy is strongly affected by waiting time.

As a technique, Equal Channel Angular Pressing (ECAP) is simple and inexpensive. However, if die manufacture and operational details are not carefully planned and implemented, difficulties arise, which can interfere with the product characteristics and the pressing operation itself. The present paper offers guidelines on die design and manufacture, emphasizing geometry, material and heat treatment. Further, operational parameters such as lubrication, pressing temperature, deformation routes, die closure procedure and the influence of channel cross section on maximum acceptable load are described. Additionally, the effects of those variables on the product characteristics (deformation level and homogeneity) and integrity, plus process control and safety, are discussed.

The tensile strength of metals and alloys can be considerably increased by severe plastic deformation, a consequence of the extreme grain refinement thus achieved. In the present work the deformation was performed by Equal Channel Angular Pressing and the material was an Al-4% Cu alloy. Characterization included tensile tests, and microstructural observation by optical and transmission electron microscopy. After four passes, the yield strength showed an increase of 310% over the undeformed alloy, a figure reduced to 160% by a 250 °C / 1 hour post - deformation anneal. Additionally, the alloy displayed a very low work hardening capacity, especially after the annealing heat treatment. After four deformation passes the grain size of the annealed specimens was estimated to be close to 500 nm. The tensile behaviour and the absence of work hardening were discussed in terms of the fine microstructure.

The present work examines microstructure, tensile properties and quality (porosity level) of two thixoformed products, namely an assembly of three cylindrical rods from which tensile samples were machined out, and a cup-shaped part. The material is an A356 aluminium alloy and the microstructural conditioning was carried out by the deformation - recrystallization technique. Additionally, the microstructures of an A356 ingot produced by the magnetic stirring process was also investigated. Results showed that solid fraction and soaking time in the semi-solid state determine the thixoforming forces, that very low porosity levels can be achieved and minimized by the maintenance of high pressures during solidification, and that the material flow during injection in the mould is relatively homogeneous, except for the material conditioned by magnetic stirring. Physical simulation experiments of the thixoforming process (rods) showed a strong correlation between liquid segregation and porosity level. Finally, the tensile properties were shown to be much higher that those of permanent cast samples.

The present work discusses some principles of materials selection and examines a few selection criteria and contexts in which this technical activity takes place. Emphasis is given to the concept of Merit Indices, and to the methodology employed for its deduction. The Materials Properties Charts and their integration with the Merit Indices are introduced and illustrated by the former of the two case studies here presented whilst the second associates the methodology of materials selection to process selection.