1996 Volume 46 Issue 11 Pages 576-581
Calcium is a useful element for the removal of silicon from the recycled aluminum melt by filtering since it reacts with silicon and forms giant intermetallic compounds. In such a procedure, calcium may remain in the melt, but its influence on various properties of aluminum alloys has not been made clear. This study is conducted for the purpose of clarifying the influence of the remained calcium on various properties of 6061 aluminum alloy from a view point of metallography. CaAl2Si2, Al3Fe and coarse Al–Mg–Cr–Ca–Cu compounds crystallize in 6061 aluminum alloy by the calcium addition. Silicon, which is contributable to age hardening in 6061 aluminum alloy, is largely contained in the CaAl2Si2 compound. The amount of silicon existing in the matrix as solute atoms is, therefore, remarkably reduced by the calcium addition, resulting in no age hardening in 6061 alloy with 0.76%Ca. As an amount of calcium addition increases, elongation and Charpy impact value increase, but tensile strength, proof strength and formability are markedly lowered because of increasing amount of the crystallized compounds and softening of matrix phase. It's required that calcium content in 6061 aluminum alloy is less than 0.1 mass% to guarantee tensile properties satisfying JIS values.
