Abstract
One of the major causes of premature failure in A319 aluminum alloy powertrain components is the accumulation of thermal stresses. Consequently, the engine operating temperature is restricted to prevent large internal temperature gradients in the components, thereby reducing thermal efficiency. The objective of this research was to investigate the influence of solidification parameters on the thermal conductivity of A319 alloy, in an effort to promote uniform temperature distributions in powertrain components. Castings with varying mould preheating temperatures were characterized using thermal analysis, microstructural analysis, mechanical testing, and thermal conductivity measurements via the transient plane source method. The results indicated that increasing solidification rate was associated with two competing phenomena: Whereas finer secondary phases improved conductivity, a finer dendritic structure reduced conductivity. As a result, a critical solidification rate was found to attain maximum thermal conductivity in A319.
Highlights
One of the major causes of premature failure in A319 aluminum alloy powertrain components is the accumulation of thermal stresses
The magnetic field generates eddy current within the material which can be monitored and related back to the material’s electrical conductivity. While such indirect techniques are suitable for measuring electrical properties, their reliance as tools for determining thermal properties is hindered by the accuracy of the mathematical relationship used, i.e. in uncertainties of the Lorenz number
This chapter describes the experimental procedure conducted to complete each stage of this study, including the design, simulation, and machining of a permanent mould, melting and casting details, thermal analysis, microstructural analysis, porosity measurements, mechanical testing, and thermal conductivity measurements
Summary
Increased fuel costs and government legislation on carbon emissions are providing the impetus for lighter and more fuel efficient vehicles. There has been much research devoted towards improving the mechanical properties of A319 and other aluminum alloys, perhaps most commonly via increasing the casting solidification rate. Direct correlations between the A319 alloy solidification conditions, microstructure and properties were developed, enabling an improved understanding of the influence of solidification on thermal conductivity These results can be used to produce lightweight powertrain components with enhanced properties that promote better fuel efficiency and conservation of the environment. This thesis has been structured as follows: In Chapter 2, a concise review of the literature available on A319 aluminum alloy, solidification mechanisms, and thermal conductivity is presented This includes the published results regarding metallurgical influences on conductivity, and concludes with an overview of various techniques for measuring thermal conductivity.
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