Intermetallics Formation, Hardness and Toughness of A413.1 Type Alloys: Role of Melt and Aging Treatments

The present work was performed on experimental Al-Si near eutectic cast alloys, with different additives, mainly Fe, Mg, Mn, Cr, Sr and P. The alloys were solidified at 0.8°C/s, very close to equilibrium conditions. Precipitated phases, primarily Fe-, Cu-, Mg-, and Sr-based intermetallics, were examined. Although the phases reported in the present work were documented previously, the range of chemical composition of each phase was confirmed using an electron probe microanalyzer (EPMA) equipped with wavelength dispersive spectroscopy (WDS) and electron dispersive X-ray spectroscopy (EDS) facilities. Some of these alloys were cast to produce hardness test samples using a metallic permanent mold preheated at 425 °C that provided a microstructure with an average dendrite arm spacing (DAS) of ~22 µm. Samples were solution heat treated at 495 °C ± 2 °C for times up to 24 h, followed by quenching in warm water (65 °C), and thereafter artificial aging at 155 °C for 5 h (T6 treatment). Hardness and impact tests were carried out on the heat-treated test bars.