The Impact of Strontium Modification on the Microstructural Characteristics and Mechanical Performance of High-Pressure Die Cast AlSi9Cu3(Fe) Alloy

The microstructure of the HPDC AlSi9Cu3(Fe) alloy is characterized by fine dendrites of α-Al solid solution and α-Al+β-Si binary eutectic mixture. In addition, the alloy contains many intermetallic phases, such as α-Al15(Fe,Mn,Cr)3Si2, β-Al5FeSi, Al2Cu, π-A8Mg3FeSi6 and Q-Al5Mg8Cu2Si6. The paper presents results of research concerning the influence of Sr-based modification on the microstructure and mechanical properties of the HPDC AlSi9Cu3(Fe) alloy. The research-related tests involved three different high-pressure die cast specimens, i.e. two castings with different Sr contents (i.e. 40 ppm and 130 ppm) and one without an Sr addition. The addition of Sr was responsible for the fragmentation of eutectic silicate crystals, which was advantageous for the microstructure of the test specimens. However, the aforesaid addition also triggered an increase in the volume fraction of porosity in the structure, which, most likely, resulted in the deterioration of mechanical properties.