Change in Sr Modification by Duration and Its Effect on Mechanical Properties of A360 and A413 Alloy

Strontium modification has many advantages for the mechanical properties of Al–Si alloys. Holding time is an important factor in Sr modification. Its high affinity to oxygen may result in forming of \( {\text{SrO}}.{\text{Al}}_{2} {\text{O}}_{3} \) spinel oxides. Therefore, Sr quantity in the melt can decrease by time due to fading. In this work, this phenomenon was investigated in A360 and A413 alloys under different casting conditions. The melt was held at 700 °C for 4 and 17 h after the addition of 300 ppm Sr. Metallographic examination was carried out to observe the change in eutectic morphology. Melt quality change was measured by means of reduced pressure test. In addition, tensile test samples were produced. It was found that there is a clear correlation between mechanical properties and bifilm index of Al–Si alloys.