INFLUENCE OF Ca, Ti, P, S AND C ON SILUMIM

Abstract

Commercial Silicon always contains Fe, Al, Ca, Ti, P, S and C as impurities, which tend to segregate as shown in Table. 1. Test bars of Silumin made from same Aluminium ingot and socalled same charge Silicon have often different values in their properties. Some proportion of impurities in Silicon is assumed to be alloyed in Silumin, but their influences on Silicon have not yet been studied. In this report influences of Ca, Ti, P, S and C on Silumin are investigated using standard Silumin and mother alloys shown in Table. 2. P and S were added in Silumin by melting the mixture of Silumin borings and P or S in hot graphite crucible, and also by charging in molten Silumin by phosphorizer, C was added in Silumin by violently starring the mixture of molten Silumin and graphite while cooling and heating again at 1000°C about one hour. Influences of Ca or Ti on mechanical properties of Silumin are shown in Table. 3, Fig. 1 and Fig. 3, Chemical compositions in Table. 4, and their microstructure and casting surface in Photo. 1-11. The results obtained are as follows:(1) Ca has modification effect on Silumin, but it is not so remarkable as that by Na. Tensile strength of Silumin containning 0.05% of Ca is equal as Silumin modified by Na, but elongation is lower. Ca over than 0.05% injures both tensile strength and elongation of Silumin, because of the appearance of CaSi2. Ca also makes casting surface of Silumin so-called toad skin disliked by founder. This phenomenon is a sort of modification in which primary Al dendrites crystalize in the normal direction to casting surface.(2) Ti less than 0.05% has little influence upon mechanical properties and microstructure.(3) P acts as nucleus of Si crystal as phosphide. C also acts as nucleus, but effect of S as nucleus is feeble.(4) Oxide that might be included, and observed in fact, above treatments, has little nucleation effect.