The Effect of Sr Modifier Additions on Double Oxide Film Defects in 2L99 Alloy Castings

Abstract

In this paper, Sr modifier (300 ppm) was added to 2L99 alloy sand castings to investigate its effect on bifilm defects in the castings. Two different sand molds were used in this study, with good and bad running system designs, to introduce different amounts of bifilm defects into the castings. The mechanical properties of the modified 2L99 castings were compared to the properties of unmodified castings and showed that with high bifilm defect contents (H) the Sr addition reduced the Weibull modulus of the UTS by 67 pct and the Position Parameter by 5 pct, and introduced a bimodal distribution into the Weibull plot of the pct Elongation. However, for castings with low bifilm defect content (L), the Weibull moduli of both the UTS and pct Elongation were significantly improved (by 78 and 73 pct, respectively) with the addition of Sr. The Position Parameter of the pct Elongation was improved by 135 pct. The results suggested that a desirable modification effect can only be achieved while the bifilm defect content in a casting was low.

Grain Refiner Settling and Its Effect on the Melt Quality of Aluminum Casting Alloys

“…The presence of the Ca-containing intermetallic compound particle can be explained by the interfacial segregation of the surface-active Ca and the heterogeneous nucleation of the compound particle on the oxide film. A similar phenomenon was reported by Al-Helal et al [ 86 ] for Al 2 CaSi 2 , as well as by Chen and Griffith [ 87 ] for Al 2 SrSi 2 compound particles.…”

Sr addition and its effect on the melt cleanliness of A356

“…Nateghian [15] had found that Al 2 O 3 was transformed into SrO when Sr content was as low as 50 ppm and after 5 h of holding, these oxides bond to each other which is known as 'healing' of the bifilms. Chen [16] reported that bifilm quantity and amount of porosity was increased when A356 was modified with Sr.…”