Effects of calcium on mechanical properties of cellular Al-Cu foams

Cellular Al-2.5Cu and Al-7Cu foams are fabricated by a melt-foaming method utilizing Ca and TiH2 as the thickening and blowing agent, respectively. No age-hardening effect is observed on the cellular Al-2.5Cu foams during the isothermal aging at 200 °C, which is distinct from the precipitation behavior of dense Al-Cu alloys. The yielding strength of cellular Al-7Cu foams increases slightly during the same aging treatment. The strength evolutions of a series of dense Al-Cu alloys containing Ca are also investigated to understand the precipitation behavior in cellular Al-Cu foams. The result shows that the unknown Al-Ca-Cu intermetallic compounds can be formed in the as-cast samples. Therefore, there is inadequate Cu in the Al matrix to form the strengthening precipitation during the aging process. Age-hardenable cellular Al-Cu foam could not be obtained by melt-foaming method using Ca as the thickening agent. The crystal structures of the Al-Ca-Cu phases are determined with the Cu content ranging from 2.5% to 9 wt%.