The modification of silicon in zinc-aluminum-silicon alloys

The purpose of this research was to refine the silicon morphology through the addition of modifying agents that were used in the binary aluminum-silicon system. Since the addition of small amounts of strontium or phosphorus in Al-Si alloys refines the size of the silicon it was proposed that the addition of these modifiers to Zn-Al-Si alloys might bring about similar refining effects.; The experimental method consisted of directionally solidifying long slender rods of varying Zn composition. By instrumenting the mold along a portion of the rods' lengths detailed information was collected for temperature gradients and freezing rates. By comparing the microstructures of the rods in locations where the freezing rates and gradients were approximately equal the effect of increasing zinc concentration and various modifiers on the silicon morphology was determined.; A Bridgeman furnace was devised with a motor-driven platform to which the sample tubes were attached; a heating element; and a copper cooling jacket. Design objectives included attaining thermal gradients between 0.1{dollar}spcirc{dollar}C/mm and 10{dollar}spcirc{dollar}C/mm and achieving repeatable and uniform freezing rates. The solidification apparatus satisfied all the design objectives.; Sample alloys were prepared and cast into alumina tubes. The alloys were remelted in the Bridgeman furnace. Standard metallographic and stereological methods were used to analyze the samples. (Abstract shortened by UMI.)...