| 摘要: | 500系鋁鎂鑄造合金屬於非熱處理型合金，一般先施以均質化處理後使用，因具有良好的車銷加工性、優異的抗蝕能力、與極佳的表面處理效果，已廣泛應用於船舶用椅、化學零組件等。當鎂含量(>3wt.%)的合金若長時間處於50~90℃溫度區間時，鎂、鋁原子會傾向於在晶界析出β-Mg2Al3，若β相在晶界上以連續方式析出，會使合金於腐蝕環境中產生沿晶腐蝕(intergranular corrosion)的敏化(sensitization)現象，導致合金原有之優異抗蝕能力大幅衰減。由於鋁鎂鑄造合金常於敏化溫度下(50~90℃)被使用，敏化是一項不易避免的製程，造成鋁鎂鑄造合金存在著對腐蝕敏感之問題，雖有文獻提出以過渡元素添加來改良敏化，但預熱之熱處理對於鋁鎂鑄造合金腐蝕敏感之影響則尚無文獻提出探討。而本研究前導性研究發現均質化鋁鎂鑄造合金(即512.0合金)，經（150~200℃）預熱處理後，在不減損合金機械性質下，可大幅提升敏化處理後的合金抗蝕性(~120%)，合作企業對此項結果，深覺有益於產品抗蝕性之提升，具有實用價值，且申請人也覺得有將其學理探討清楚之必要，故提出本計畫之申請。合作公司近年接獲大量船用鑄鋁合金訂單，其中尤以512、A514合金為大宗，客戶期望鑄件能在不減損機械特性下(UTS>280Mpa, YS>130Mpa, elongation>20%)，能滿足ASTM-G67之抗蝕規範要求(<15mg/cm2)，所以期望藉本研究，提升鋁鎂合金之鑄造、機械性質、抗蝕性等技術與知識，以增進實際應用的確切性，在學理上也能供學界有價值且正確之理論參考。 ;The 500-series Al-Mg alloys are non-heat-treatable casting alloys. Generally, used after homogenization, and been widely used in ship chairs because of its good machinability, excellent corrosion resistance and surface finishing, etc. When the Mg content is >3wt.%, alloy in the range of 50~90°C for a long time, Mg and Al tend to precipitate β-Mg2Al3 at the grain boundary. If the β phase precipitates in a continuous manner on the grain boundary, The sensitization phenomenon of the intergranular corrosion of the alloy in a corrosive environment results in a significant attenuation of the original excellent corrosion resistance.Since Al-Mg casting alloys are often used at sensitizing temperatures (50-90 °C), sensitization is an unavoidable process, causing the problem of Al-Mg casting alloys being sensitive to corrosion. Many literature proposes transitional elements(La, Ce etc..) to improve sensitization, However, the effect of preheating heat treatment on the corrosion sensitivity of Al-Mg casting alloys has not been discussed in the literature. I our preliminary study of this field found that the homogenized Al-Mg casting alloy (ie, 512.0 alloy), after pre-heat treatment (150~200 °C), can greatly enhance the alloy corrosion(~120%) after sensitization treatment without detracting from the mechanical properties of the alloy.This result is beneficial to the improvement of the corrosion resistance of the product, and it has practical value. We also feels that it is necessary to discuss its theory clearly, so the application for this project is proposed. .In recent years, the cooperative company has received a large number of orders for marine cast Al-alloys, especially 512 and A514 alloys. Customers expect that the castings can meet ASTM-G67 specification (<15mg/cm2) without detracting from mechanical properties (UTS>280Mpa, YS>130Mpa, elongation>20%). Hence, it is expected to enhance the technology and knowledge of casting, mechanical properties and corrosion resistance of Al-Mg alloys by this research to enhance the accuracy of practical application. It can provide valuable and correct theoretical references for the academic community. |
