Development of Cerium-Reinforced Specialty Aluminum Alloy with Application of X-ray and Neutron Diffraction

Abstract

The growing demand for increased power output and efficiency of automobiles has led to the recent effort of improving the high-temperature properties of the currently used powertrain alloys. Research into the effects of rare earth additions, such as cerium (Ce), to aluminum (Al) alloys has been gaining momentum due its high-temperature stability associated with its unique Ce-bearing intermetallics. In this study, scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction and neutron diffraction analyses were performed to characterize the microstructure of an Al–6%Ce, Al–16%Ce and an Al–8%Ce–10%Mg alloy. It was observed that the microstructure of the two binary alloys was occupied primarily with fine interconnected Al–Ce eutectic. Additionally, blocky primary Al₁₁Ce₃ precipitates were observed in the Al–16%Ce alloy. The large difference in coefficients of thermal expansion between Ce and Al is presumed to be one of the factors leading to the observed extensive microcracking of the primary Al₁₁Ce₃ precipitates in the Al–16%Ce alloy and consequently reducing the alloys’ ductility. This reduction in ductility has large implications in terms of usability of the alloy for the targeted powertrain applications. The microstructure of the Al–8%Ce–10%Mg alloy was characterized for the first time and largely consisted of Chinese script or blocky Al₁₁Ce₃ precipitates surrounded by a Mg-rich Al matrix. It was found that in addition to solid solution strengthening, the Mg addition may be a factor in altering the fine interconnected Al–Ce eutectic to the coarser Chinese script morphology. This Chinese script morphology is one of the factors restricting dislocations and contributing to the increased strength of the Al–8%Ce–10%Mg alloy at high temperatures, therefore making the alloy suitable for the most demanding engine applications.