The Effect of Strontium on the Strength of Layers of Double Oxide Film Defects

Abstract

The change in the strength of layers of oxide film (bifilm) defects when held in Al-0.05 and 0.1 wt pct melts was evaluated indirectly by comparing the porosity, average pore roundness, and pore number density results obtained from a reduced pressure test of the commercial purity and Sr-containing Al melts subjected to different holding and vibration regimes. Any changes in the composition of the pores were also studied using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that the Al 2 O 3 layers of a newly formed oxide film defect, when held in Al-0.05 or 0.1 wt pct Sr melt, transformed gradually into an Sr-containing oxide. This transformation caused the strength of the oxide layers to increase and the rate of the expansion of its atmosphere and removal of the defect from the melt to decrease. This might influence the increase in the porosity of Sr-modified Al castings.

Archives of Metallurgy and Materials

“…12), however, revealed Fe 2 O 3 to form predominantly on the surface of the samples at relatively short reaction times. Such change in the preferencial formation of oxides was also observed by Bartar-Esfahani et al [24] and Najafzadeh et al [25] for the formation of Al 2 O 3 at the presence of Sr and Mg, respectively, in the Al melt and Rao et al [21] for the formation of Fe 2 O 3 at the presence of Al in the Fe melt. The later researchers attributed it to the low concentration of Al compared to Fe in the protective layer (in the present experiments measured to be 10 and 90 at% for Al and Fe, respectively [13]) which not only caused very few nucleation of Al 2 O 3 but also the inability of the alloy to supply Al for the growth of the existing Al 2 O 3 [ 26 ] .…”

Al-12Si Alaşımlarında Yüzey Oksit Uapısının Sr Varlığında Değişimi

“…In order to achieve higher fluidity and mechanical properties, Al-Si alloys are modified with strontium. However, according to researchers in the area [2][3][4][5][6][7][8], there are various discussions on whether strontium generates porosity in those alloys or not. Many scientists claim that strontium modification increases the amount of oxides in the melt and these oxides results in porosity.…”