| Summary: | 碩士 === 國立虎尾科技大學 === 材料科學與綠色能源工程研究所 === 100 === Vanadium modified aluminum grade A6061 alloys were manufactured by lost foam casting process. The homogenization, solution treatment and artificial aging schedules were optimized to obtain superior hardness and confirmed chemical composition within the crystals of the solid solution was uniform. Then, the effect of the modified alloys on the microstructure and mechanical properties were evaluated.
The results show that the time to achieve homogenization annealing increases with increasing of the alloy vanadium content. A minimum time necessary for a complete homogenization is 48 hours when the vanadium content exceeds 1.11%. As the vanadium element increases, the artificially aging time increases. Meanwhile, the hardness of modified alloy also increases remarkably with increasing vanadium content. Increasing vanadium content reduces ductility but increases tensile strength, yield strength and fatigue life. The SEM analysis of the tensile fracture surface shows that the tensile fracture surfaces show obvious dimple feature. With increasing vanadium additions, the dimple fracture translates into the mixed mode of quasi-cleavage and dimple fracture. The microstructure indicates that vanadium additions also effectively decrease the grain sizes. Besides, precipitates forming along the grain boundaries are found; most significant in Al-Mg-Si alloys are Al9Si phase and Mg2Si phase. It is found that vanadium additions can significantly promote the formation of Al3V phase at the grain boundaries. Since vanadium contains up to 4.4% that leads to the both Al3V phase and Al10V phase are present in the grain boundaries.
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