Effect of metallurgical parameters on the microstructure, hardness impact properties, and fractography of Al-(6.5–11.5) wt% Si based alloys.

The present study was performed on 356 and 413 alloys containing various amounts of hydrogen (H 2 ), titanium diboride (TiB 2 ), and strontium (Sr). The results show that the eutectic silicon particles in non-modified alloys undergo coarsening during the solutionizing treatment. High energy levels are obtained when the alloy is degassed, Sr-modified, and grain refined. Precipitation of Mg 2 Si phase particles in 356 alloys is more effective as a hardening agent than the Al 2 Cu phase precipitated in the 413 alloy which contributes to the alloy strength/hardness. The increased Si content in non-modified 413 alloys accelerates crack initiation and propagation, leading to low toughness values. Modifying the 413 alloys with 200 ppm Sr results in a more even distribution of the spheroidized eutectic Si particles and hence better the alloy toughness. Exceeding the required amount of Ti-containing grain refiner may result in the introduction of a large amount of brittle Al 3 Ti platelets that would reduce the alloy toughness. [ABSTRACT FROM AUTHOR]