| 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。 B535.0(Al-7Mg-0.15Ti)為一含高鎂鑄造鋁鎂合金，具有良好的抗蝕能力與焊接性，其T5態強度與延性分別可達260MPa與10％，已被廣用於具腐蝕環境下的船艦結構體與航空用材等，由於B535.0合金之鎂含量高達7wt %，此合金具有極高之固溶強化與加工強化性，和些微散佈強化效應，以致常被認為成型性不佳，不易做成鍛件使用。但經合作公司（金全興）實地測試，發現此合金具有極佳之熱加工與冷加工性，可成功製成鍛造之線材與板材(暫命名為MB5350合金，M：modification)。 然此合金（MB5350合金）是否有良好耐蝕性，是此鍛造材是否有實用價值的關鍵。由於鋁鎂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，合作企業限於本身的研發能力，無法對此主題有效研發，為能解決實務問題與原理瞭解，故委請本案，期能增進實際應用的確切性，並在學理上能供有價值之理論參考。 本研究前導性研究發現，MB5350鍛造合金，經（250~300℃）安定化處理後，藉由ASTM-G67規範，其硝酸腐蝕重量損失測試[ASTM1]值約為17mg/cm2，僅略高於不具沿晶腐蝕敏感性的15mg/cm2（但並不嚴重），但難得的是其（T5態）機械強度可達325MPa，延性也達12％，均優於B535.0合金。合作企業對此項結果，深覺有實用機會，且申請人也覺得利用熱處理學理，期能克服沿晶腐蝕敏感性略高之問題，另外，也有將其學理探討清楚之必要，故提出本計畫之申請。 ;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. While 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 network 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. B535.0(Al-7Mg-0.15Ti) is a cast aluminum-magnesium alloy containing high magnesium. It has good corrosion resistance and weldability. Its T5 strength and ductility can reach 260MPa and 10% respectively, and it has been widely used in ship structures and aviation materials under corrosive environment. The magnesium content of B535.0 alloy is as high as 7wt%, this alloy has extremely high solid solution strengthening and working strengthening, and slightly dispersion strengthening effect, so often regarded as poor formability, not easy to use as forgings. However, tests by a partner company (JinQuanxing) found that this alloy has excellent hot and cold workability, and can be successfully made into forged wires and plates (temporarily named MB5350 alloy). However, whether this alloy (MB5350 alloy) has good corrosion resistance is the key to whether this forged material has practical value. Since aluminum-magnesium alloys are often used at the sensitization temperature (50~90℃), sensitization is an inevitable process, which causes the aluminum-magnesium casting alloy to have a problem of being sensitive to corrosion. The cooperative enterprise is limited to its own research and development capabilities. This topic cannot be effectively researched and developed to solve practical problems and principles. Therefore, this case is requested to improve the accuracy of practical applications and provide a theoretical reference for the theory. The leading of this study found that MB5350 forged alloy, after being stabilized at (250~300℃), was tested by ASTM-G67, its nitric acid corrosion weight loss test value was less than 18mg/cm2, only slightly higher than 15mg/cm2 without intergranular corrosion sensitivity. (But not serious) But it is rare that its (T5 state) mechanical strength can reach 325MPa, and the ductility also reaches 12%, which is better than B535.0 alloy. The cooperating enterprise deeply felt that there was a practical opportunity for this result, and the applicant also felt that the use of heat treatment theory could overcome the problem of slightly higher sensitivity to intergranular corrosion. In addition, it was also necessary to discuss its theory clearly, so this project was proposed. |
