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%.