- 學位論文
多道次等通道彎角擠製製程對6061鋁鎂矽合金顯微組織與機械性質之影響
The Effect of Multi-pass Equal Channel Angular Extrusion Process on Microstructures and Mechanical Properties of 6061 Al-Mg-Si Aluminum Alloy
摘要
利用等通道彎角擠製(ECAE)之激烈變形製程具有許多優點，擠製過程可藉由改變擠製方位進一步達到控制材料織構的目的。經過多道次擠製過程可使材料內部累積大量的塑性變形，且擠製後材料截面積並不會產生改變，同時經退火再結晶後可獲得均勻且細晶的材料結構，晶粒細化對塊狀金屬而言是十分重要的強化機制。 本研究利用等通道彎角擠製法對6061鋁合金進行不同道次擠製，並施以再結晶退火，以得到不同晶粒大小之結構。擠製後鋁合金試樣經由微觀結構分析及機械性質測試以了解擠製道次對微結構變異及機械性質之影響；並對擠製後及細化後之鋁合金試樣進行固溶、淬冷及人工時效之T6處理，以了解T6處理對擠製及晶粒細化鋁合金機械性質的影響。 研究結果發現，藉由改變擠製道次及退火溫度可製備不同晶粒大小結構之試樣，擠製道次對6061鋁合金機械性質有顯著的影響，在單一道次可以有效提升材料抗拉強度與硬度，在4道次達到最大值；而擠製道次超過8次後，隨著擠製道次的增加，道次對6061鋁合金機械性質的影響逐漸減小。擠製道次對晶粒大小亦有顯著的影響，在12道次可將晶粒細化至80-100nm。經T6處理的擠製試樣，其抗拉強度與硬度不太受擠製道次影響；但伸長率隨擠製道次的增加而增加。8道次擠製試樣於500℃進行3小時之退火製程可完成再結晶，但對12道次擠製試樣而言，此退火製程將導致晶粒出現異常成長，使試樣硬度下降。
關鍵字
等通道彎角擠製並列摘要
There are many advantages of using equal channel angular extrusion (ECAE) process for severe plastic deformation (SPD) of metallic materials. The texture structure of extruded bulk material can be controlled with changing the route during extrusion processing. The large plastic deformation can be accumulated and the cross-sectional area will not change in extruded bulk material through multi-pass extrusion process. Also it will obtain a homogenous and ultra-fine grain structure as the extruded materials were heat treated by recrytallizational annealing. Grain refinement plays an important role on strengthening mechanism of bulk metallic material. In this study, the heat-treatable 6061aluminum alloy bulk materials were extruded by equal channel angular extrusion with different passes. Microstructures with different grain sizes can be obtained by annealing the extruded bulk materials at recrytallizational temperature. The analysis of microstructures and measurement of mechanical properties on the extruded aluminum alloy specimens were conducted to reveal the effect of extrusion pass and annealing temperature on microstructures and mechanical properties. The extruded and grain refined aluminum alloy specimens were heat treated by T6 treatment (i.e. solution heat treatment, quenching and artificial aging).The correlation of the T6 treatment with mechanical properties of the extruded and the grain refined aluminum alloy specimens will be established. The results show that the specimens with structure of different grain sizes can be prepared by different extrusion pass and annealing temperature, the extrusion pass has a significant effect on mechanical properties of 6061 Al-Mg-Si aluminum alloy. The single pass can effectively enhance the tensile strength and hardness, and both will reach a maximum value at 4 passes. But both tensile strength and hardness will gradually decrease with the increasing pass as extrusion pass exceeds 8 passes. The extrusion pass also can significantly affect the grain size, the grain size can be refined to 80-100nm with 12 passes by ECAE process in 6061 Al-Mg-Si aluminum alloy. The extrusion pass only has a negligible effect on the tensile strength and hardness of the extruded aluminum alloy specimens that were heat treated by T6 treatment; but the % elongation will increase with the increasing pass. The extruded specimens with 8 passes can be completely recrystallized by annealing treatment at 500℃for 3 hours. But the hardness of the extruded specimens with 12 passes, which were heat treated by this annealing treatment, will decrease due to abnormal grain growth.