1 Introduction

    Cast aluminium alloys have widespread applications for structural components in the automotive industry. For example, in power-train applica-tions, including engine blocks, cylinder heads and transmission cases. However, to achieve the maximum impact on fuel efficiency, the application of cast aluminium alloys needs be extended to more critical structural parts, such as brake valves and callipers which are traditionally made of cast  iron and steels. The most significant barrier to the acceptance of cast aluminium in many structural applications has been its reputation for variability in mechanical properties. Anything that may help predict and/or control the results of casting variables would be of great benefit to industry.

    Mechanical properties are linked to the microstructure in the material, which is determined by the chemical composition (trace elements and alloying elements) and casting conditions (solidification rate and casting defects). In practice, solidification occurs under non-equilibrium con-ditions which can be modelled using the so-called Scheil-Gulliver approach. This approach has proved to yield excellent results for phase evolution in aluminium alloys [1] and will be adopted in the present study.

    Typical casting microstructural features consist of primary phases (dendritic Al phase or primary silicon particles), eutectics (Al-Si, Al-Al2Cu, Al-Al3Mg2 etc.) and intermetallics (AlFeSi, Al5Cu2Mg8Si6 etc.), all of which are considered in the strength model. The model developed here differs from previous work on mechanical properties [2,3,4], in that it can be applied to a wide range of commercial aluminium alloys and the calculations are carried out in an automatic fashion.

2. Calculation of Microstructural Features

2.1 Phase Evolution During Solidification

    The phase evolution in aluminium alloys during casting can be modelled straightforwardly via the so-called Scheil-Gulliver approach [1], which can be carried out using thermodynamic calculations [5]. It provides the necessary information for further property modelling, such as phase fractions and composition. For instance, the information for hypoeutectic Al-Si alloys includes the fractions of primary Al phase, the Al-Si eutectic and the percentages of the Al and Si phases in the Al-Si eutectic. The fractions of other possible eutectics, as well as secondary intermetallics formed during solidification, can also be calculated.

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