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Aluminum alloys are generally used in transportation-related applications where weight saving is of paramount interest. In addition to aluminum's density advantage related to other metals, weight can also be saved by the use of thin walled components. However, there are limited ways to make complex shape, thin walled, high integrity castings at high volumes. One such way is semi-solid metal (SSM) casting. In the past, minimum wall sections for semi-solid castings have been limited to the range of 2 to 3 mm (0.08 to 0.12-inches). Heat transfer from the semi-solid aluminum to the cooler steel of the die surfaces limits the minimum section thickness. The high heat transfer rates restrict the distance that the semi-solid slurry will flow, prior to the heat loss to the steel causing the alloy to solidify and thereby stop flowing. This paper will describe techniques to produce semi-solid castings with much thinner sections.