臺灣博碩士論文加值系統

　　本研究針對航空用7050鋁合金，探討合金主成份（Zn和Mg）對強度與延伸率的影響，從而釐清熱處理與強度的關係，並藉由控制微結構求改善抗應力腐蝕破壞性。主要利用微分掃描熱分析儀（DSC）、穿透式電子顯微鏡（TEM）以及拉伸測試（tensile test）等方法。
　　由實驗的結果顯示：Mg含量固定時，強度隨著Zn含量的提高而提升，但延伸率則無明顯的關係。Zn含量固定時，Mg含量提高，強度有先降後升的趨熱，延伸率經T6 、T73、階段式淬火後亦隨之提高，但經復元再時效後反而隨之降低。此外，固定Zn＋Mg含量，強度會隨著Zn／Mg比提高而上升。其原因是因為Zn／Mg比越高，就越接近強化相MgZn2的比（5.38:1）。
　　合金主成份為Zn＝6.19％，Mg＝2.55wt％時，有最佳的強度，若再經階段式淬火處理後，可得兼具高強度與高抗應力腐蝕破壞性的航空用7050鋁合金。

　　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.