Effect of Fe, Mn and Sr on the Microstructure and Tensile Properties of Secondary Al-Si-Cu-Mg Cast Alloys

Abstract

This paper presents results on the effect of Sr, Fe and combined additions of Fe and Mn on the microstructure and tensile properties of a secondary Al-Si-Cu-Mg alloy. The microstructure features of base alloy consisted mainly of a structure with primary Al-matrix, coarse acicular Si particles and intermetallic phases such as Al2Cu and AlCuNi. When 0.02%Sr was added to the base alloy, coarse acicular Si particles were modified to a fine fibrous form. With addition of 0.38%Fe, results in the formation of large eutectic silicon particles and Fe rich intermetallic. Moreover, when 0.45%Mn was added in combination with 0.9%Fe, the Al2Cu, and α -AlFeMnSi with Chinese script morphology were identified. It is noticed that after T6 heat treatment, the Si particles are seen to spheroidize and fragment while the Al2Cu phases dissolve completely. These changes lead to improved mechanical performance of the alloy. The addition of strontium decreases the ultimate Tensile strength and increases percent elongation while addition of low iron and iron with manganese decreases UTS and percent elongation in the as cast condition. T6 heat treatment increases the ultimate tensile strength while ductility decreases due to the fragmentation and spheroidization of eutectic silicon particles. Keywords—