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?. Abstract
It is supposed to get the microstructure and hardness of aluminum alloy treated different aging times and temperatures. One of the samples is left as control group and the others, 5 samples, are solid solution treated at 450�� for 24hr. Etch three samples is aged at 100��, 150�� and 200�� for 10 hr, and the others, etch two samples is aged at 150�� for 1hr and 24hr. After the heating treatment, the microstructure observation and hardness test is followed. Eventually, the various precipitates by different aging condition are formed so that the hardness of the samples tends to show the various values by this creation of the precipitates.
In the metallography observed by optical microscope, the precipitate free zone is shown around grain boundary. And the incoherent precipitate can be observed on the grain boundary. As a result, at the aging temperature 100�� for 10hr the highest hardness is measured.

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