微結構對5083-H116船用鋁合金晶間腐蝕及應力腐蝕之影響

Effects of Microstructural Evolution on the Intergranular Corrosion and Stress Corrosion Cracking Susceptibility of 5083-H116 Alloys

本研究主要藉由ASTM G67硝酸腐蝕重量損失測試（nitric acid mass loss test，NAMLT）、慢應變速率拉伸試驗（slow strain rate testing，SSRT）、硬度試驗及微結構觀察，探討5083-H116船用鋁鎂合金在100～450°C退火及敏化處理後的微結構變化對晶間腐蝕及應力腐蝕敏感性之影響。實驗結果發現，微結構影響β相析出之形態，而β相析出連續性是造成晶間腐蝕及應力腐蝕之重要誘發因子。其中，退火溫度在200°C以下的合金敏化處理後，晶界連續析出β相（Mg2Al3），導致嚴重的晶間腐蝕及高應力腐蝕敏感性；於200～250°C退火及敏化後，β相於晶界不連續析出，合金呈現較佳的抗晶間腐蝕性能及低應力腐蝕敏感性；300°C以上退火及敏化後，合金已開始再結晶並具有嚴重的晶間腐蝕現象，但因低強度及高延展性，應力腐蝕敏感性稍為下降。 Microstructural changes in 5083-H116 alloy under different annealing temperatures and sensitization treatments. The properties of annealed and sensitized samples of 5083-H116 were investigated using microhardness measurements, scanning electron microscope (SEM) and optical microscopy (OM). Nitric acid mass loss testing (ASTM G67 NAMLT) and slow strain rate testing (SSRT) were conducted to examine the influence of different microstructure on the intergranular corrosion (IGC) and stress corrosion cracking (SCC) susceptibility of 5083-H116 alloys. The results indicated that the alloys annealed below 200°C and upon 300°C, high IGC and SCC susceptibility were experienced, induced p-phase (Mg2AI3) precipitation in the form of a continuous layer along the grain boundaries. High IGC and SCC resistance attained after annealed at the temperature range 200-250°C due to the discontinuous β-phase precipitated at grain boundaries.