本文是以商用A206鋁合金為基礎，分別添加不同比例的Fe及Mn，以研究此二元素的含量對A206鋁合金拉伸性質的影響；另外也對不同鐵含量對破裂韌性及疲勞裂縫成長特性的影響加以研究。研究中使用光學顯微鏡、電子顯微鏡/電子微探儀(EPMA)、影像分析、導電度量測及熱差掃描分析(DSC)等來觀察材料的微結構。拉伸性質試驗的結果顯示，Fe的增加會使針狀Cu2FeAl7富鐵相的體積分率成比例增加；Mn的增加會抑制針狀富鐵相的形成，使其轉為較圓的中文字型富錳相。高錳合金於鑄造時，部分的錳元素會固溶在基地中，於固溶處理時會析出Cu2Mn3Al20 顆粒，因而阻止其晶粒的成長。針狀、富錳相及Cu2Mn3Al20 等顆粒均會導致鋁基地中的銅固溶量降低；同時，增加鋁基地中的錳含量會延緩強化相的析出。DSC分析顯示θ'的析出動力及析出量會隨著Fe 及Mn含量的增加而降低，尤其以錳的添加為甚。Cu2Mn3Al20 顆粒的析出及其所導致的較小晶粒會增加高錳合金於固溶狀態時的硬度，而T7狀態的硬度則由θ' 相的析出量來決定。Fe含量的增加會使合金的強度以接近線性的方式遞減，延性更是大幅下降。Mn含量的增加對提升低Fe合金的機械性質之效果不明顯；在高Fe合金，Mn含量的增加會使降伏強度降低，抗拉強度則未有明顯的變化，然而會使延伸率大幅增加。 關於鐵含量對破裂韌性及疲勞裂縫成長特性的影響方面，由於Cu2FeAl7顆粒的斷裂及與基地剝離所形成的空孔，會加速A206合金的破裂過程。增加鐵含量會增加Cu2FeAl7顆粒的體積分率，會導致在區域II及III的裂縫成長速率增加並會降低破裂韌性。在A206合金的破裂過程中，Cu2FeAl7顆粒的破裂模式會影響裂縫延伸速率。在低ΔK (或K)時其破裂模式大多為斷裂，對裂縫延伸的影響較小；而當ΔK (或K)增高時，與基地剝離數量逐漸增多而產生較大的劈裂平面，對裂縫延伸的影響較大。增加鐵含量會輕微降低合金的起始應力強度因子ΔKth，這是由於增加鐵含量會降低其機械強度。 The effects of Fe and Mn contents on tensile properties and effects of Fe contents on fracture toughness and fatigue crack growth behaviors of aluminum-base A206 alloys were investigated. Optical microscopy, scanning electron microscopy/electron microprobe (EPMA), image analysis, electrical conductivity and scanning differential calorimetry (DSC) were used to examine the microstructures of alloys. Results of tensile properties showed that the addition of Fe caused a loss in both ductility and yield strength. Further addition of Mn can recover the ductility, but it caused a further loss in yield strength, and caused no change in tensile strength. In low Mn alloys (0.29 wt% Mn) the primary constituent was the needle shape of Cu2FeAl7, when further addition of Mn the Chinese script of Mn-bearing formed instead. The Cu2Mn3Al20 particles formed in high Mn alloys during solution treatment and resulted in grain growth inhibition. The needle, Mn-bearing and Cu2Mn3Al20 particles cause the solid solution level of copper in matrix to decrease; meanwhile, increasing the Mn solution level retards the precipitation of strengthening phase. DSC analyses show the kinetics and amount of θ' phase precipitation decrease when the contents of Fe and/or Mn are increased. The smaller grain size induced by the Cu2Mn3Al20 particles and the θ' phase are the factors that determine the hardness of A206 alloys under as-quenched and T7 treated conditions, respectively. The fracture processes of A206 alloys are accelerated by void nucleation at Cu2FeAl7 particles as a result of their cracking and decohesion from the matrix. Increasing the Fe content will increase the volume fraction of Cu2FeAl7 particles, which induced higher crack growth rates in regions II and III and reduced fracture toughness. The fracture mode of Cu2FeAl7 particles dominates the crack extension behaviors of high-Fe contained A206 alloys. In low ΔK (or K), the fracture morphology of the particles is mostly in cracking mode. With increasing ΔK (or K), the sites of the particles decohered from Al-matrix increase, associated with big flat cleavage surfaces accelerating the crack extension. The effect of Fe on decreasing threshold stress intensity rangeΔKth is more apparent in higher Fe-content alloy than in lower Fe-content alloys. It is ascribed to the greater mechanical strength in lower Fe-content alloys.
