6069鋁合金熱壓縮變形之熱加工性及動態行為分析;Hot workability and dynamic behavior analysis of 6069 aluminum alloy under hot compression

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Title:	6069鋁合金熱壓縮變形之熱加工性及動態行為分析;Hot workability and dynamic behavior analysis of 6069 aluminum alloy under hot compression
Authors:	朱峯君;Zhu, Feng-Jun
Contributors:	機械工程學系
Keywords:	6069鋁合金;動態回復;動態再結晶;製程加工圖;應變硬化行為;軟化行為;相對軟化行為;顆粒輔助之異常晶粒成長;AA6069 aluminum alloy;Dynamic recovery;Dynamic recrystallization;Processing map;Strain-hardening behavior;Softening behavior;relative softening behavior;Particle-Assisted Abnormal Grain Growth
Date:	2017-07-19
Issue Date:	2017-10-27 16:16:04 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究為6069鋁合金鑄錠經均質化處理之熱變形特性探討，使用Gleeble-3500熱加工模擬試驗機來進行熱壓縮實驗，實驗條件為300-500℃及應變速率0.001-10 s-1。從熱壓縮實驗之流變應力數據分別繪製成製程加工圖來分析可加工區域之熱變形條件，並且在可加工區域從顯微結構角度又可為成動態回復和局部動態再結晶之兩大區域。此外，由功率消耗效率圖也能進一步得知兩個區域中顯微結構變化的差異。其中動態回復區域之功率消耗效率約為中等，另一方面局部動態再結晶的功率消耗效率則較高。非加工區又稱作不穩定區，則是由局部變形來證明是不可採用之顯微結構。也從流變應力計算之應變速率敏感指數(m值)等值線圖分析，得知局部變形發生之熱變形條件，其m值都是較低。最後，熱變形動能分析則在局部動態再結晶區域中，發現隨著溫度提升、表面活化能是隨之降低。不同熱壓縮條件，會影響顯微結構在經過固溶、時效處理後的變化，主要分界點為流變應力60MPa，經過熱處理會形成巨大的晶粒組織，主要機制為顆粒輔助之異常晶粒成長。另外則是低溫、高應變速率(流變應力> 60MPa)的條件經熱處理後，其機制為靜態再結晶。第三種高溫、低應變速率(流變應力< 60MPa)經熱處理後，則是形成長條狀的回復晶粒，機制是次晶界遷移。透過EBSD分析動態再結晶的顯微結構演化、發現高於500℃及應變速率低於0.1 s-1的條件可以觀察到動態再結晶。且透過晶粒尺寸分布及晶界取向差分布發現6069鋁合金的動態再結晶機制屬於連續動態再結晶。透過相對軟化與應變之間的關係，可以分析該熱變形條件的軟化機制。相對軟化因子變化趨勢可分為三類：其一、相對軟化因子隨應變增加至0.5而增加，而後增加應變量時則維持持平之狀態。此條件在變形後段時，應變硬化與動態軟化達成平衡。其二、相對軟化因子則呈現連續增加直到應變0.7。此類型的軟化機制是低應變以動態回復為主；高應變仍有動態回復並且另外加入局部動態再結晶。其三、相對軟化因子則隨著應變增加而遞減，此類型則代表應變硬化率高於動態回復的軟化效應。 ;In this study, these tests were examined using Gleeble-3500 thermal simulation machine at temperature range of 300-550 °C and a strain rate range of 0.001-10 s−1. These examine were via hot compression tests. Hot workability of homogenized 6069 Al alloy cast ingot was investigated using processing map. The processing map was constructed from compression data, through which identified a safe processing region. The microstructure and value of safe processing contour could divided into dynamic recovery and dynamic recrystallization domains. The variation in microstructure was related to the variation in efficiency of power dissipation (value of processing contour), as indicated by microstructure observations. Dynamic recovery and partial dynamic recrystallization was related to intermediate and high efficiency of power dissipation in safe regions, respectively. The microstructure of flow instability region was founding flow localization, which indicates non-working region. Those deformation conditions observation flow localization were corresponding to the low m values of strain rate sensitivity m map. The kinetic analysis revealed a decrease in apparent activation energy with increased temperature in the partial dynamic recrystallization region. The microstructural evolution analyzed via electron backscatter diffraction. Dynamic recrystallization is recognized during deformation at temperatures higher than 500 °C/strain rates lower than 0.1 s-1 that showed the operating mechanism of dynamic recrystallization was related to continuous dynamic recrystallization. A relative softening factor was used to quantify the effect of flow softening, which was reveal softening mechanisms at the hot deformation condition. The variations in the relative softening value with strain that divided three type. First, the value of relative softening initially increases with strain up to a peak and then reaches a ﬁnal steady state. This condition speciﬁes that DRV balances strain-hardening. Second, the relative softening value continuously increases with strain. This ﬁnding illustrates that continuous softening is caused by DRV at low strains and DRV with partial DRX at high strains. Third, the progressive decrease in the relative softening value shows that the rate of strain-hardening is higher than that of softening of DRV.
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