| Effects of Cd addition on the aging characteristics of Al-Cu-Mn-Ti-Zr alloy were investigated usimg scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The air-melted Al-Cu-Mn-Ti-Zr alloy ingots with and without Cd were solution treated at 543℃ for 13 hours, followed by water quenching. Aging treatments were carried out at 170℃ up to 24 hours. In case of Cd-containing allays, the accelerated age-hardening makes the peak hardness higher than that of Cd-free alloys. It is due to the fact that Cd atoms stimulate θ′(CuAl₂) precipitates and increase the density of θ′ precipitates by forming Cd-clusters, which are known to act as heterogeneous nucleation sites of θ′ precipitation With increasing Cd contents up to 0.2%, peak hardness and tensile strength were increased. But beyond 0.2% Cd contents, peak hardness and tensile strength were deteriorated because of localized segregation of Cd atoms. The elongation was, maintained up to 0.15% Cd contepts, but decreased rapidly beyond 0.15% Cd contents. Therefore, it can be inferred that the optimum contents of Cd in Al-Cu-Mn-Ti-Zr alloy is about 0.15. |
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