兩階段熱機處理對Al-Mg-Sc 合金機械性質之影響

Abstract

本實驗採用Al-6Mg-0.81Mn-0.4Sc-0.13Zr(wt％)合金來探討不同輥軋加工條件對於合金的低溫及高溫拉伸性質之影響。藉由熱差分析儀、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、機械性質、超塑性及顯微組織的變化。 實驗結果顯示，此合金最佳的超塑性拉伸溫度為530℃，當真應變率固定為5x10-3/s時可獲得465％的伸長率。此合金經過冷輥軋處理後之主要變形機構為溶質拖曳潛變，其m值為0.27；而經過兩階段熱機處理後之主要變形機構則改變為晶界滑移，m值為0.48。由此可知，不同的加工製程會影響材料的高溫變形機制。此外，此合金的強化機構及微觀之變形特性，主要是由Al3（Sc,Zr）與差排滑移時之間所產生的交互作用所控制。經實驗可發現細小的Al3（Sc,Zr）除了有結構強化及整合強化，還具有Orowan強化機構。

This study was to investigate the influence of different rolling conditions, such as the two-step thermomechanical process（TMP） and cold rolling, on the tensile properties of Al-Mg-Sc alloy at room temperature and high temperature. The microstructure, annealing characteristics, mechanical properties and superplastic properties of this alloy were studied by using differential thermal analysis（DTA）, microhardness measurements, SEM, TEM and tensile test . The maximum tensile elongations found in Al-6Mg-0.81Mn -0.4Sc-0.13Zr(wt％) alloy at 530 ℃ is 465％ which occurred under a strain rate of 5×10-3/s. The main deformation mechanism of this material which was produced by a treatment of TMP is grain boundary sliding （GBS） with a high strain rate sensitivity of m=0.48；the sample produced by cold rolling is mainly controlled by the solute-drag mechanism due to a smaller strain rate sensitivity of m= 0.25. It indicates that different rolling conditions affect the deformation mechanism of materials. It is noted that the strength mechanism and microstructure characteristics are controlled by Al3（Sc,Zr）precipitates which react with dislocations. The experimental results show that Al3（Sc,Zr）particles exhibit structure strengthening, coherent strengthening and the Orowan mechanism.