中文摘要：
	本研究針對5052及5182兩款鋁-鎂合金，藉由在不同位移速率下之拉伸性質、軸向V型凹痕試片之NSR值、JIC值及疲勞裂縫延伸速率之比較，來瞭解此兩款鋁-鎂合金相關破裂性質之優劣性。此外，亦利用掃描式電子顯微鏡(SEM)，對兩款鋁-鎂合金破斷面加以觀察分析，以瞭解破斷面上凹窩大小與其延韌性質之關係。實驗結果顯示，兩款鋁-鎂合金在不同位移速率之拉伸性質，不論在慢或快速率拉伸下，5182比5052具有較佳之降伏/抗拉強度，且受基地中固溶鎂原子產生動態應變時效之影響，造成兩款鋁-鎂合金應力應變曲線在超過降伏點以後會呈鋸齒狀之變化及抗拉強度在拉伸速率≧200 mm/min的條件下有明顯下降的趨勢。比較兩款鋁-鎂合金之NSR值，鎂含量較高的5182其NSR值比5052來得低，顯示其具有較低的凹痕韌性。另外，鎂含量較低之5052鋁-鎂合金其JIC值較5182鋁-鎂合金為高，而JIC值愈高代表材料破裂韌性較佳，有較佳抵抗裂縫成長的能力，因此5052比5182鋁-鎂合金有較慢之疲勞裂縫成長速率。此外，兩款鋁-鎂合金在R = 0.1、0.5及0.7三種不同荷重比下的疲勞裂縫成長行為，可以用裂縫閉合效應解釋之。由SEM觀察中得知，5052及5182兩款鋁-鎂合金在破斷面上皆有明顯凹窩結構，且鎂含量較低韌性較佳的5052鋁-鎂合金比5182鋁-鎂合金有較大且深之凹窩。另外，從兩款鋁-鎂合金在裂縫延伸的過程中，發現會有因為裂縫延伸產生裂縫尖端塑性鈍化而形成疲勞紋路。
Abstract：
	This study was to characterize and compare the fracture properties of two commercial aluminum alloys, 5052 and 5182, in terms of tensile properties in various stroke rates, NSR values, JIC values and fatigue crack growth rate (FCGR). Fractography analyses were conducted with scanning electron microscopy (SEM) to determine the relation between dimple sizes and fracture toughness. Results from tensile tests in various stroke rates for 5052 and 5182 aluminum alloys indicated that ultimate and yield strength are higher in 5182 than in 5052. This is due to the enhanced solution strengthening effect generated by the greater amounts of magnesium in 5182. The stress-strain curves were serrated and ultimate tensile strength was reduced at higher stroke rates in both aluminum alloys as a result of the dynamic strain aging effect. NSR and JIC values are higher in 5052 than in 5182 indicating the greater fracture toughness and better crack growth resistance in 5052. Results of FCGR testing showed that FCGR was lower in 5052 than in 5182 because of the superior fracture toughness in 5052. In addition, fracture crack growth behavior of 5052 and 5182 aluminum alloys in different load ratios could be rationalized by crack closure effect. Fractography analyses indicated the fracture surfaces of 5052 and 5182 aluminum alloys exhibited a typical ductile fracture mode with the existence of extensive dimples. Dimples were bigger and deeper in 5052 than in 5182, implying the greater ductility possessed by 5052. The fatigue striations were readily observed in stable crack growth regions for both aluminum alloys.