鋅-22 wt.﹪鋁合金之加工軟化與退火硬化研究

A Study on the Strain Softening and Anneal Hardening in Zn-22 wt％ Al Alloy

余育陞(Yu-Sheng Yu)

指導教授 ： 楊智富

大同大學/工程學院/材料工程學系所/碩士(2005年)

摘要

本研究利用熱機處理來製備細晶(d = 0.3 μm）與粗晶(d = 2 μm)結構之鋅-22 wt.% 鋁合金，並探討其加工行為與退火硬化行為。藉由示差掃瞄熱卡計 (DSC) 、微硬度、及壓縮測試，並且配合掃瞄式電子顯微鏡 (SEM)微觀組織之觀察，探討鋅-22 wt.% 鋁合金之微觀結構與加工軟化及退火硬化的關係。研究結果顯示，在-10℃至250℃之溫度區間鋅鋁合金會出現加工軟化之現象，而軟化後之鋅鋁合金在後續高溫退火時會出現退火硬化之現象。由實驗結果分析得知，加工軟化之機構乃是熱加工時之動態再結晶(DRX)所導致之軟化行為，而具備高角度晶界之極細β相晶粒可促進動態再結晶，而加強加工軟化之效果。另一方面，退火硬化之機構則是藉由退火消除(粗化)這些極細β相晶粒，阻礙動態再結晶所導致之軟化，回復材料正常強度。
為進一步驗證加工軟化之機構，本研究針對壓縮實驗所得結果提出一「複合應力-應變圖形」模型來解析鋅鋁合金內所發生之結構變化，對應於此「複合應力-應變圖形」，鋅鋁合金內個別α相與β相所發生之塑性變形行為與動態再結晶（應變軟化）行為均得以清楚辨別。

關鍵字

鋅-22 wt.﹪鋁合金 ； 加工軟化 ； 退火硬化

並列摘要

In this study thermomechanical processings were applied to a Zn-22 wt.% Al alloy to produce fine- and coarse-grained structures for the strain softening and anneal hardening studies. The microstructure, hardness and compression curve of Zn-22 wt.% Al alloy were studied by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), microhardness measurements and compression tester. The results showed the occurrence of a strain softening phenomenon in the Zn-Al alloy in the temperature range from -10℃ to 250℃ and an anneal hardening behavior in the softened Zn-Al alloy upon high temperature annealing. The mechanism of the strain softening behavior was found to be the DRX-induced softening during hot working, which can be facilitated by the formation of ultra-fine β grains with high-angle-boundaries; the mechanism of the anneal hardening behavior, on the other hand, was the annihilation of the ultra-fine β grains by a high temperature grain coarsening treatment to retard the occurrence of the DRX-induced softening and to restore the “normal strength” of the alloy.
A composite stress-strain curve model was proposed in this study to resolve the mechanism of strain softening in the Zn-22 wt.％ Al alloy. By using this model detailed informations regarding to the deformation and the DRX (i.e. the strain softening behavior) in individual α and β phases were disclosed from the experimental compressive stress-strain curve.

並列關鍵字

anneal hardening ； strain sofening ； Zn-22 wt.﹪Al

參考文獻

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