本研究藉由含微量鈧、鋯之Al-4.5Mg-0.8Mn合金探討以下主題： (1)經電子束焊接(electron beam welding，EBW)後，微量鈧、鋯對Al-4.5Mg-0.8Mn-H116合金板材微結構、機械及腐蝕性質之影響；(2)藉由高溫熱處理模擬實驗，探討含微量鈧、鋯之Al-4.5Mg-0.8Mn-H116合金焊接時熱影響區之特性變化。 Al-4.5Mg-0.8Mn合金微量添加鈧、鋯元素，可使鑄態合金之晶粒細化，提升鑄態合金硬度，並抑制再結晶現象，經高溫退火後仍保有原熱加工組織，使合金機械強度提升，主要強化機制為Al3Sc、Al3Zr及Al3(ScxZr1-x)晶出相所造成的細晶強化、散佈強化，以及抑制再結晶的次結構強化。 高溫熱影響區模擬試驗中發現，Al-4.5Mg-0.8Mn-H116合金在600℃熱處理後其腐蝕重量損失率皆大幅上升，有嚴重的沿晶腐蝕現象，主要是因高溫時合金部分溶解，導致大量β相(Mg2Al3)晶出於晶界，造成嚴重的沿晶腐蝕破壞；而添加鈧、鋯元素的晶粒細化效果，反讓β相有更多析出位置，提供連續的腐蝕傳播路徑，使腐蝕面積增加，裂縫更能深入材料內部，導致合金抗蝕能力衰退。This present study investigates the Al-4.5Mg-0.8Mn alloys containing minor scandium, zirconium and discusses the following topics :(1)Effect of Sc, Zr additions on the properties of Al-4.5Mg-0.8Mn alloys after electron beam welding (EBW). (2)Investigating the characteristics of Al-4.5Mn-0.8Mn alloys in welding process by simulated heat affected zone (HAZ). Additions of minor Sc, Zr to Al-4.5Mg-0.8Mn alloys not only refine the cast ingots, but also improve hardness. The precipitations can prevent recrystallization even at high temperature and remain fibrous microstructure via hot working. Strengthening increment by adding Sc and Zr is mainly attributed to fine-grain strengthening, dispersive precipitate strengthening and substructure strengthening resulted from recrystallization restricted. Al-4.5Mg-0.8Mn-H116 alloys have considerably mass loss after heat treatment at 600℃ because alloys have been dissolved partially and β-phase (Mg2Al3) precipitated abundantly at grain boundary, dense precipitation of β-phase in Al-4.5Mg-0.8Mn alloys containing Sc and Zr since the small grains have more boundaries which provide the β-phase nucleation locations and corrosion propagation path, the corrosion crack penetrate into the material further and result in the corrosion resistance of alloys decline significantly.
