Light alloys: from traditional to innovative technologies

Selection of materials with the expected, application-dependent characteristics constitutes a very important point in any industrial application. In the automotive and aeronautical industries, the current tendency is to use light metals and their alloys for production of various components. For example, some of the problems related to fuel consumption and weight reduction could be partially solved by using such alloys as an alternative to traditional iron-based alloy components. Due to their very attractive properties, the most commonly employed light materials for producing high-stressed components are aluminium, magnesium and their alloys. Al-based alloys have a high strength/weight ratio, good formability, excellent combination of castability and mechanical properties which together with an excellent corrosion resistance make them very appropriate for a large variety of applications. There are two important families of aluminium alloys: (i) wrought alloys, firstly cast as ingots and/or billets and then mechanically hot- and/or cold-worked into the preferred shape, and (ii) cast alloys, directly cast into their final form through different traditional or innovative processes. At the same time, there is continuing interest in Mg alloys for engineering proposals because of their lowest density directly connected to a weight saving of about 40% compared to steel and cast iron and 20% compared to aluminium for the same component performance. Their high specific strength, good castability and machinability, high thermal conductivity, high dimensional stability, good electromagnetic shielding property, high damping characteristics and full recyclability place them in a particular position for production of different types of components. High-pressure die casting is the most widely used technique and represents about 50% of all light alloy casting production. The tendency to use low-pressure die casting is increasing (it accounts for about 20% of all production). Gravity die casting, a small but growing contribution derived from a vacuum die casting and squeeze casting process, represents the remaining share of manufacturing processes. Generally, during solidification in a traditional manufacturing process, volume contraction is observed. This is due to the wrong feeding system and/or gas development, which in turn generate some voids or cavities within a casting, which are in turn responsible for the presence of defects in the casting components. For these reasons, the research community and manufacturing industries are giving a high level of attention to the development of innovative production procedures. In this context, semi-solid metal processing is able to attain at least the same level of properties and performances as those obtained by conventional techniques. Progresses in materials development represent a valid support for enhancing the life of an engineering component and its reliability. In this chapter, a general overview of the actual scenario concerning the production and use of light alloys will be presented, including a short history and description of state-of-the-art techniques integrated with some results of the current research in this field carried out by the authors.