Copyright 2019 American Foundry Society
Abstract – Aluminum alloys 357 and 356 are widely used workhorse alloys for military, aerospace and commercial applications. These alloys combine excellent casting characteristics with moderate strength. Silicon combines with the magnesium in these alloys to form Mg2Si which strengthens the alloys. The Si levels exceed what is required for the strengthening mechanisms and excess Si is added to improve fluidity, hot tear resistance and feeding characteristics. Improvements in metal cleanliness and casting techniques over the years suggest that the amount of Si can be reduced, without significantly affecting casting characteristics. Mechanical properties of lower Si alloys show a significant increase in ductility with minor reductions in tensile strength. The quality index increases in E357 as Si levels are reduced from 7 to 4%.
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