Grain Refinement of Non-Ferrous Metals

You achieve grain refinement by adding small amounts of nucleating agents to the melt before solidification. They cause many small crystals to form instead of fewer large ones. A fine grain gives you a tougher and more crack-resistant structure. If you use too much of the additive or the temperature isn't right, the structure can become uneven. Make sure to stir the additive evenly into the melt and keep cooling under control, then the grain will be nicely uniform.