National Research Council of Canada. NRC Institute for Aerospace Research
Text, Book Chapter
In aluminum alloys one of the most pervasive and important impurity elements is iron, stemming from the impurities in bauxite ores and the contamination of ferrous metals such as melting tools. Since iron has a very low solid solubility in aluminum (max. 0.05%), almost all iron in aluminum alloys is present in the form of second intermetallic phases. One of the most common Fe-rich intermetallics that form in cast and wrought aluminum alloys upon solidification is the β-Al₅FeSi phase. This phase has long been thought to be brittle and responsible for the inferior mechanical properties (in particular ductility) of aluminum cast alloys. The commonly accepted method to ameliorate the harmful influence of iron is the addition of one or more corrective elements. Such additions generally convert the β-Fe platelets into α-Fe dendrites. Various studies have been carried out by researchers on the modification of β-Al₅FeSi intermetallics in aluminum alloys using Mn, Cr, Co, Mg, Sr, Li and Be. The relative effectiveness of these elements is collected and compared in the present review. The mechanisms for the action of the chemical modifiers are critically reviewed particularly in the light of the modern theory of their nucleation on oxide films present in aluminum melts, probably in large populations. The new insights into the Fe-rich phase in aluminum alloys will aid in better understanding the role of iron in aluminum alloys.
Nova Science Publishers
Materials Science Research Trends (2008): 251–271.