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題名 | 鈹與鐵對Al-Si-Mg鋁合金疲勞裂縫延伸之影響=Effects of Beryllium and Iron Fatigue Crack Growth Rate of Al-Si-Mg Alloys |
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作者 | 譚安宏; 鄭榮瑞; 林於隆; 羅德祐; 李勝隆; | 書刊名 | 鑄工 |
卷期 | 23:3=94 1997.09[民86.09] |
頁次 | 頁15-27 |
分類號 | 472.5 |
關鍵詞 | 鈹; Beryllium; |
語文 | 中文(Chinese) |
中文摘要 | 本研究是探討富鐵相、矽粒子和Mg Si析出物對Al-Si-Mg鋁合金疲勞裂縫延伸 速率之影響。加鈹在含高鐵的Al-Si-Mg鋁合金中,對於提升起始應力強度ΔK 的影響, 比添加在含中或低鐵的合金顯著。加鈹於高鐵或中鐵之Al-Si-Mg鋁合金,其疲勞壽命有明 顯改善。含中鐵或高鐵鋁合金中的富鐵相是疲勞裂縫的起源。當合金具有較大的機械強度及 較彎曲的裂縫路徑所引發的裂縫閉合和橈曲,可在區域I的低疲勞裂縫成長速率得到較高的 ΔKth。含鈹合金具有較大的破裂韌性及較低的裂縫成長速率,使得在區域Ⅱ及Ⅲ之高疲勞 裂縫成長區具有較優越的抗疲勞裂縫延伸性。在靠近起始裂縫成長區的破裂面為階梯狀及類 劈裂面;隨著裂縫成長速率增加,其破裂面的粗糙度增加,且在區域Ⅱ形成疲勞條紋;在高 疲勞裂縫成長區,其破裂面則以韌渦和劈裂面為主。 |
英文摘要 | An investigation of iron-bearing compounds, silicon particles and Mg Si percipitates on fatigue crack growth behavior in Al-Si-Mg alloys has been performed. The effect of Be on increasing Kth is more apparent in alloys with higher Fe content than in alloys with medium and lower Fe content. The fatigue life of the higher and medium Fe contents Be-containing alloys will be improved much as well as that of in the lower Fe contents of alloys. Major fatigue cracks induced by cracking of iron-bearing compounds cracking were found in the medium and higher Fe-content alloys. In the lower Fe content alloys, irregular silicon particles appear to be the main source of fatigue crack nucleation. In region I of low fatigue crack growth rates, the higher threshold stress intensity is attributed to the greater mechanical strength and to enhanced roughness-induced crack closure and deflection from more tortuous crack paths. The superior fatigue crack propagaion resistance at higher growth rates of regionsⅡ and Ⅲ is attributed to greater fracture toughness and to reduce the crack growth rates in the Be-containing alloys regardless of Fe levels. The fracture surface morphologies of near-threshold crack growth contain stepped patterns and cleacage-like facets. With increasing crack growth rate, the fracture surface roughness increases and striations are formed in region Ⅱ. At higher fatigue crack growth rates, the formation of a dimple surface and cleavage plane replace striation formation. |
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