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Civil and Environmental Engineering


The use of cast aluminum components in automotive applications is increasing rapidly. Cast Al components are allowing the industry to meet the current as well as future customer and legislative requirements regarding vehicle size and performance.

The 319 Al alloy, which contains 3-4wt%Cu and 6-7wt%Si, is utilized in Ford automobile engine block castings. After heat treatment, this alloy exhibits higher yield and tensile strength levels than other grades of cast Al alloys. However, some other mechanical properties of the 319 Al alloy need to be improved, and thus a lot of these alloys are not applicable for engine blocks. The bulkhead section of the engine block is susceptible to high cycle fatigue (HCF) during operation. Recent IRC work showed that it might be possible to improve microstructures and mechanical properties of 300-series of cast Al alloys through the optimization of Si, Cu and Sr levels in the castings.

This project concerns the optimization of Si, Cu and Sr contents for the improvement of microstructures and properties of 300-series casting Al alloys, particularly HCF properties. In order to investigate the effects of chemical composition and cooling rate (CR) on microstructures and properties, six plates with various chemical compositions were cast at Ford CPDC. The plates were chilled at one end so that temperature gradients and different CR were created.

This research project has investigated the effects of chemical compositions (Si, Cu and Sr), temperature gradient and CR on the microstructures, properties and casting defects of the Al alloys typically utilized for automotive engine blocks. A criterion has been developed for the improvement of next-generation engine component durability through the optimization of chemical compositions, and solidification conditions. The influences of heat treatment parameters on Cu phase(s) area fractions and hardness have also been investigated.

The experimental work performed showed that the secondary Dendrite Arm Spacing (SDAS), Silicon Modification Level (SML), Porosity Area Fraction (PAF), Cu phase(s) area fraction (CuAF) and hardness were affected by the CR. Slight changes on the above parameters were caused by microalloying changes.