| 摘要: | 本研究藉由微結構分析，探討錳、鋅與均質化處理對Al-4.6Mg鑄造合金機械及腐蝕性質之影響。
結果顯示錳與鋅元素具有固溶強化效果。而添加錳之合金更有細晶效果，且於均質化溫度下（480℃）會充分析出細小之MnAl4相，故於室溫下顯現細晶與散佈強化效果，其中均質化後水淬之合金，固溶在鋁基地中的鎂原子較經爐冷之合金為高，致使水淬比爐冷之合金顯現較高之固溶強度，然而均質化後不論水淬或爐冷之合金，其在鋁基地中固溶的錳原子含量相近，並不造成固溶強度差異。而含鋅之合金在爐冷過程中雖會析出η相(MgZn2)，因析出量較少，故均質化後不同冷卻方式對強度影響主要以β相(Mg2Al3)析出，造成固溶的鎂原子消耗為主。
合金經(200℃X3天)敏化處理後，因均質化後水淬狀態比爐冷狀態擁有較高的鎂過飽合度，在敏化初期(1天)於晶界上會析出連續緻密且細小的β相(Mg2Al3)，但敏化達3天時，則β相(Mg2Al3)粗化而成不連續態。當合金中同時含有鋅時，經敏化3天後，β相(Mg2Al3)雖會粗化而不連續，但結合η相(MgZn2)卻會在晶界上而形成連續態，其中當合金同時含有錳與鋅元素時，因錳元素所導致的細晶效果，提供更多β相(Mg2Al3)與η相(MgZn2)成核位置，致使合金受到最嚴重的沿晶腐蝕破壞。
藉由均質化爐冷製程，雖會降低合金強度，但因爐冷過程中的部分鎂及鋅原子會析出β相(Mg2Al3)與η相(MgZn2)，在後續的敏化處理，將會導致β相與η相粗化，彼此間距較遠，造成不連續的析出相，可改善η相對合金腐蝕性之傷害，但其抗蝕能力仍較不含鋅合金差。
The study analyzes microstructure of Mn, Zn and homogenization treatment on Al-4.6Mg casting alloy mechanical and corrosive properties.
The results show that both Mn and Zn elements come with solid solution strengthening effects. On the other hand, alloy added with Mn offers refinement and can fully precipitates fine MnAl4 phase under homogenization temperature (480℃), which there by exhibiting refinement and dispersion strengthening effect under room temperature. In particular, the alloy having undergone homogenization quenching will have more magnesium atoms of solid solution in the aluminum base than alloy undergone furnace cooling, resulting in higher solid solution strength for quenching alloy than furnace-cooling alloy. Nonetheless, the alloy, regardless of quenching or furnace-cooling after homogenous treatment, will have similar content of Mn atoms for solid solution in the alloy base without causing difference between the solid solution strength. Although alloy containing Zn will precipitates η phase (MgZn2) during the furnace-cooling process, the main impact comes from the precipitation of β phase (Mg2Al3) using different cooling method after homogenous treatment, which hence leads primarily to the consumption of magnesium atoms in the solid solution.
Having undergone the sensitization treatment (200℃X3days), the quenching state for alloy after homogenization treatment will have higher magnesium saturation than furnace cooling state, while consecutive, delicate and fine β phase (Mg2Al3) will be precipitated on the grain boundary at early sensitization period (Day 1). However β phase (Mg2Al3) will become coarse and discontinued on the 3rd day of sensitization. When alloy contains Zn at the same time, although β phase (Mg2Al3) will become coarse and discontinued after 3 days of sensitization, it will combine with η phase (MgZn2) and forms consecutive state on the grain boundary. In particular, when the alloy contains Mn and Zn elements concurrently, the Mn elements will lead to grain effect, providing more nuclear position for β phase (Mg2Al3) and η phase (MgZn2), causing alloy to suffer from the most serious damage of intergranular corrosion.
Although the homogenization furnace-cooling process could lower alloy strengthen, the β phase (Mg2Al3) and η phase (MgZn2) precipitated by some Mg and Zn atoms during the furnace cooling process, the follow-up sensitization treatment will cause β phase and η phase to become coarse. Nonetheless, the further gap between the two causes discontinued precipitation phase to improve the relative damage of η to alloy corrosion while its anti-corrosion capacity is still worse than alloy without containing Zn. |
