單、雙相鋅-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 Pseudo-single- and Dual-phase Zn-Al Alloys

詹育碩(Yu-Shuo Chan)

指導教授 ： 楊智富

大同大學/工程學院/材料工程學系所/碩士(2006年)

摘要

本研究利用熱機處理來製備具不同預應變之三種鋅鋁合金，包括微雙相鋅-22 wt.% 鋁及擬單相之鋅-95 wt.% 鋁(α相)與鋅-1 wt.% 鋁(β相)，探討其是否及如何發生加工軟化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，探討三種合金內之α相與β相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℃之溫度區間含大量β相之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來粗化這些極細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與退火硬化對鋅鋁合金之應力-應變行為，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-22 wt.% 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β相所發生之塑性變形行為、動態再結晶(應變軟化)行為與粗化(退火硬化)均得以清楚辨別。

關鍵字

鋅鋁合金、加工軟化、退火硬化、動態再結晶

並列摘要

In this study thermomechanical processings were applied to three Zn-Al alloys, namely the micro-duplex Zn-22 wt.% Al alloy, pseudo-single α phase Zn-95 wt.% Al and pseudo-single β phase Zn-1wt.% Al for the strain softening and anneal hardening studies. The microstructure, hardness and compression S-S curves of these Zn-Al alloys 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 Zn-Al alloys containing a substantial amount of β phase in the temperature range from -10℃ to 250℃ and an anneal hardening behavior in the strain softened Zn-Al alloys upon high temperature annealing. The mechanism of the strain softening behavior was found to be a 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 found to be 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 strain softening and anneal hardening behaviors in the dual-phase Zn-22 wt.％ Al alloy. By using this model detailed informations regarding to the deformation, the DRX (i.e. the strain softening) and the grain coarsening (i.e. the anneal hardening) behaviors in the β phase can be disclosed.

並列關鍵字

Zn-Al alloy ； work softening ； anneal hardening ； dynamic recrystallization (DRX)

參考文獻

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