過時效處理對超高強度Al-8.55%Zn-2.65%Mg-2.48%Cu鋁合金超塑性之影響

本實驗採用Al-8.55Zn-2.65Mg-2.48Cu-0.1%Zr-0.06%Sc (wt％)合金來探討過時效處理對於合金的高溫拉伸性質之影響。藉由熱差分析儀、X光繞射儀、微硬度及超塑性之測試，並配合掃瞄式及穿透式電子顯微鏡，來分析合金之退火性質、超塑性以及顯微組織的變化。實驗結果顯示，此合金最佳的超塑性拉伸溫度為400℃，當應變速率為5x10-4/s時可獲得421％的伸長率。於此拉伸條件下，觀察到拉伸過程中可能伴隨著第二相部分溶解的情形，提供超塑性變形中所需的塑性流，增加變形能力。此外，過時效熱處理所產生的析出物使得再結晶晶粒大小受到抑制，促進晶界滑移。另外，於顯微組織觀察中發現到，合金中添佳的鈧與鋯會在基地內形成細小的Al3(Sc,Zr)析出物，除了強化效果外，還可以細化晶粒，提升超塑性性能。

關鍵字

超塑性；過時效；析出

並列摘要

In this research, an Al-8.55Zn-2.65Mg-2.48Cu-0.1%Zr-0.06%Sc (wt％) alloy was utilized to study the tensile properties at high temperatures. Differential Scanning Calorimetry(DSC), X-ray diffractometer (XRD), microhardness measurements, Scanning electron microscopy(SEM), and Transmission electron microscopy (TEM) were applied to analyze the annealing property, superplasticity and microstructural evolution. The result shows that the best tensile elongation at 400℃ was 421％ under 5x10-4/s strain rate. Under such tensile condition, partial dissolution of the second phase was observed, which provided superplastic flow during superplastic deformation. In addition, the precipitation after overaging process effectively suppressed the size of crystals of recrystallization as a result of facilitating the grain boundaries sliding. Moreover, it was observed in microstructure that the added scandium (Sc) and zirconium (Zr) in the alloy led to Al3(Sc,Zr) segregation which not only enhanced the strength but also reduced the grain size and promoted superplasticity.

並列關鍵字

superplastic ； overaging ； precipitation

參考文獻

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國際替代計量

過時效處理對超高強度Al-8.55%Zn-2.65%Mg-2.48%Cu鋁合金超塑性之影響

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