Characterization of a Cast Al-Cu Alloy for Automotive Cylinder Head Applications

In this study, the influences of solidification rate and grain refinement on the microstructure, hardness and electrical conductivity of a novel Al-Cu alloy for automotive cylinder heads were investigated. The influence of solution heat treatment temperature on the microstructure and hardness was also investigated. Thermal analysis, optical microscopy, SEM-EDX, Rockwell hardness and eddy current tests were conducted to provide a comprehensive characterization of the Al-Cu alloy. The results showed microstructural refinement with increasing solidification rate and with TiBor addition. Increased cooling rate through mold temperature control and the addition of TiBor had a synergistic effect on the solidification rate, resulting in a 28% increase in hardness. The predominant phase in this alloy was found to be Al2Cu. As well, Al-Zr and Al-Fe-Cu-Mn phases were also observed exhibiting a blocky morphology. The conductivity measured from the castings was approximately 28% IACS. The electrical conductivity of the alloy was not influenced by solidification rate; however, TiBor additions reduced the conductivity slightly. Preliminary solution heat treatment experiments demonstrated that the maximum temperature can be increased to 540 °C, without incipient melting. The correlations developed in this study elucidate opportunities for further enhancement of materials for automotive applications.