The Relationship between Residual Amount of Sr and Morphology of Eutectic Si Phase in A356 Alloy

Abstract

This paper studied the relationship between the residual amount of Sr and the morphology of the eutectic Si phase in A356 obtained through different modification treatment processes; additionally, the cooling rates of molds were studied. The eutectic Si phase revealed a satisfactory modification effect at residual Sr amounts above 0.01 wt % in A356 alloys cast using an iron mould. Complete modification of the eutectic Si phase could be achieved at a Sr additive amount 0.03 wt % in an A356 melt. The addition of higher amounts of Sr (~0.04–0.06 wt %) did not improve the modification effect. With the addition of 0.06 wt % Sr into A356 alloy melt and holding at 750 °C, the anti-fading capacity of Sr modification effect could be sustained for 120 minutes. More Sr is needed to obtain a good modification of eutectic Si for an A356 alloy cast using a sand mold.

Al-12Si Alaşımlarında Yüzey Oksit Uapısının Sr Varlığında Değişimi

“…Eguskiza [25] had found that after 5 hours of holding A356 in liquid state had caused up to 40% of Sr loss from the matrix which had resulted in formation of SrO on the surface. A similar finding was reported by Zhang [26] where it was claimed that 150 minutes was good enough for A356 holding at 750 o C for the fading of Sr. According to SEM-EDS and XPS results, it can be seen that the surface oxide consists of Si and thereby SiO2 is formed.…”

Determination of Optimal Modifier Level for Eutectic Silicon Phase in Hypoeutectic AlSi7Mg0.3Cu0.5 Cast Alloy

“…The previously determined loss rate constant (k) and surface reaction rate constant (k s ) offer a method for quickly estimating the fading of Na and Sr under production and/or experimental settings. The applicability of these constants for quantifying modifier fading is validated through literature data (Zhang et al 2019). Figure 7 presents experimental findings on the fading of Sr during its retention in a small laboratory furnace (with a surface area of approximately 0.015 m 2 ).…”

Influence of Alloying Element Mg on Na and Sr Modifying Al-7Si Hypoeutectic Alloy

“…To the best of our knowledge, the relation of the presence of coarse eutectic silicon and π phase has been rarely reported in the literature. In the Sr-modified A356 alloy, Zhang et al [24] observed that the eutectic silicon near the π(Al 8 FeMg 3 Si 6 ) phases always exhibited incomplete modification. Nevertheless, some partially modified eutectic silicon was also observed in the sites without Fe at the edge of the eutectic structure in their research.…”

“…The reason for the degradation of modification was attributed to the formation of (Mg 2 SrAl 4 Si 3 ) compounds. Zhang et al [24] suggested that the partially modified eutectic silicon was related to the formation of π(Al 8 FeMg 3 Si 6 ) phase in Sr-modified A356 alloy. Chacko et al [25] suggested that the modification efficiency of Sr deteriorated with the addition of Mg.…”