Anneal hardening phenomena of the cold worked Al-Zr alloys (Zr content 0.016-0.39 wt.%) were investigated and the anneal hardening mechanism of Al-Zr alloys based on these phenomena was studied.
Effects of Zr content and precipitation treatment prior to the cold working on the anneal hardening, and the aging characteristics were investigated by means of micro-hardness measurements supplemented with micro-structure (TEM) and X-ray diffraction. Also, the anneal hardening phenomena in the various Al base alloys (Fe, B, Cr, Ni, Mg, Rare Earth elements with Zr) were investigated.
The experimental results are as follows:
(1) The temperature at which the anneal hardening appeared was about 160℃.
(2) The effect of Zr content on the anneal hardening was increased with increasing Zr content and saturated at about 0.2 wt.% Zr.
(3) The anneal hardening was not observed when specimens were precipitation treated prior to the cold working and this suggests that Zr which contributes to the anneal hardening is solid solution Zr and not precipitated Zr.
(4) The anneal hardened Al-Zr alloys were stable at high temperature (270℃) than that of not anneal hardened.
(5) It is concluded that the anneal hardening mechanism of Al-Zr alloys is combination of Cottrell effect and precipitation hardening.
(6) Addition of alloying elements such as Fe, B and Cr were very effective on the anneal hardening but Ni, Mg, Rare Earth elements were not.
(7) When the above elements were added with Zr, their effects on the anneal hardening were increased and this effect is remarkable in Rare Earth elements.
