Effects of Fe-Addition as a Beneficial Modifying Element on the Microstructure and Mechanical Properties of an Al-Si-Cu-Mg-Ni-Mn Piston Alloy

Due to the combination of desirable properties, Al-Si-Cu-Ni-Mg alloys are widely used to process pistons used in diesel oil automotive engines. In this research, the effects of adding different Fe contents to the composition of an Al-Si-Cu-Mg-Ni-Mn piston alloy on the modification of Mn-rich intermetallics (MRIs) phases existing in the microstructure and consequent effects on the mechanical properties of this alloy were investigated. These were done using optical microscopy, scanning electron microscopy, x-ray diffraction, differential scanning calorimetry and transmission electron microscopy techniques and tensile tests. Improvements in the mechanical properties of Al-Si-Cu-Mg-Ni-Mn piston alloys by Fe-addition were attributed to the transformation of slender rod-like Al13Mn4Si8 phases into less harmful dendritic Al-15(MnFe)(3)Si-2 ones and a decrease in the amount of porosities existing in the microstructure of parts. The Al-Si-Cu-Mg-Ni-Mn piston alloys having different Fe contents demonstrated high-performance mechanical properties, superior to those of commercial aluminum alloys, at 350 degrees C. This behavior was attributed to the existence of thermally stable MRIs and Al3CuNi in the microstructure of these alloys.