Study on the modification of aluminium-silicon alloy (20%Si) by polytetrafluoroethylene (1st Report)

Abstract

The study was made mainly on the changes of grain size of primary silicon and eutectic structure, and those of specific gravity in aluminium-silicon alloy (20%Si) treated by polytetrafluoroethylene. The results obtained are summed up as follows:
(1) The grainsof primary silicon in the alloy are remarkably refined by adding polytetrafluoroethylene, or polytetrafluoroethylene together with negligibly small amount of phosphorus to the alloy.
(2) The most effective temperature when polytetrafluoroethylene is added, is 800°C.
(3) The most effective amount of polytetrafluoroethylene is 0.025%, where maximum size of primary silicon grain gets 0.02mm. But when more polytetrafluoroethylene is added, the effect of modification is reduced, because of unsatisfactory decomposition of polytetrafluoroethylene, and consequently the specific gravity of alloys is lowered.