| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 86 ===
This study was to research the effect of main alloy content (Zn and Mg) on the strength and elongation in order to clatify the relation between heat treatment and the strength of 7050 aluminum alloy for aerospace. Controlling microstructure was simultaneously to improve the stress corrosion cracking. Differential scanning calorimetry (DSC), transmission electron microscope(TEM), and tensile test were used.
The results showed: The strength was increased with Zn content when Mg contant was constant. But the elongation did not depend on Zn content. When Zn content was constant, the strength was first decreased and then increased as Mg content increased. The elongations treated by T6、 T73、step-quenching were decresased as Mg content increased, but RRA was contradicted. Additionally the strength was increased with Zn/Mg ratio when Zn+Mg content was constant. The cause was that the higher Zn/Mg ratio was, the more close it was Zn/Mg ratio of precipitate MgZn2(5.38:1).
The best strength was attained when Zn was 6.19wt% and Mg was 2.55wt%. Therefore, the high strength and high SCC resistance of 7050 aluminum alloy for aerospace could be obtained at the same time by the optimum alloy content and step-quenching heat treatment.
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