Effect of silicon particles and roughness on the surface treatments of cast aluminum alloys

Over the last years, shape memory alloy materials have seen widespread usage in mechanical and automotive applications. The shape memory effect is the material’s ability to recover large mechanically-induced strains (up to 8%) by temperature increase. NiTi’s remarkable behavior is due to the presence of two material phases, the martensite stable at low temperature and the austenite stable at high temperature, and the presence of a thermoelastic martensitic transformation. By means of shape memory alloy materials, the component gains the ability to adjust itself to external stimuli automatically. Furthermore, the increasing attention on low energy consumption opens the way to a larger employment of such materials. In this context, a study dealing with power reduction in engine cooling fans, through integration of shape memory alloy wires, is presented. The goal of the paper is to highlight that shape memory alloys are successful, replacing mechanical/pneumatic devices, in the design of engine cooling fans. In particular they are able to actively modify their geometry according to operative conditions, in order to reduce the fan power absorption. NiTi shape memory alloy wires, pre-deformed in the martensitic state, are integrated in the blades’ structure and able to produce a macroscopic deformation when thermally activated. In this way, according to the temperature perceived by the NiTi wires, the blades’ configuration of the fan automatically modifies. As a consequence, the flow rate can be actively controlled with respect to the cooling requirement. Some relevant material properties, such as transformation temperatures, elastic moduli of the two material phases, maximum recoverable deformation and other constants, required for describing stress-temperature and strain-temperature dependences, have been determined experimentally. Thus, the design of a fan able to guarantee the necessary cooling flow rate in steady state conditions, but able to minimize power absorption when cooling conditions are not critical, has been performed. Comparing the simulated power absorptions of the fan in the critical and non critical conditions, it has been possible to quantify the improved cooling efficiency of the fan integrated with shape memory alloy wires