退火溫度對AA5083-H15鋁鎂合金沿晶腐蝕與應力腐蝕性質之影響

Effects of annealing temperature on stress corrosion cracking and intergranular corrosion of AA5083-H15 alloys

陳彥豪(Yen-Hao Chen)

指導教授 ： 李勝隆

國立中央大學/工學院/機械工程學系/碩士(2012年)

摘要

本研究藉由拉伸、抗蝕以及慢應變拉伸(SSRT)測試，探討退火溫度及敏化處理對AA5083-H15鋁鎂合金之機械性質、沿晶腐蝕與應力腐蝕破壞性之影響。分別以光學顯微鏡(OM)、穿透式電子顯微鏡(TEM) 以及掃描式電子顯微鏡(SEM)觀察合金的微結構變化、腐蝕形貌與破裂斷面。
AA5083-H15鋁鎂合金在低於200℃的退火處理(即敏化處理)會導致β相(Mg2Al3)於晶界連續析出，此連續析出相提供腐蝕傳播的路徑，導致合金嚴重的腐蝕破壞。AA5083鋁鎂合金於敏化處理中易使β相於晶界連續析出導致抗蝕性下降。而經250℃退火的合金於敏化處理過程能減少β相在晶界上連續析出，導致腐蝕的傳播路徑不連續而擁有良好的抗蝕性。
經敏化處理後，未經退火及低於200℃退火之AA5083合金因抗蝕性低，在腐蝕環境中進行慢應變拉伸會產生嚴重的應力腐蝕現象，導致延性大幅下降；而250℃退火之合金具優異的抗蝕性，無明顯的應力腐蝕現象；高於300℃退火的合金因低強度之特性，應力腐蝕裂縫不易成長，對應力腐蝕的敏感性較低，於慢應變拉伸試驗無明顯的延性損失。

關鍵字

AA5083鋁鎂合金 ； 沿晶腐蝕 ； 應力腐蝕 ； β相(Mg2Al3)

並列摘要

Effect of annealing temperature and sensitization treatment on mechanical behavior, intergranular - corrosion property and stress – corrosion cracking susceptibility of AA5083-H15 alloys were estimated in this research. Optical microscopy(OM), Transmission Electron Microscopy(TEM) and scanning electron microscope(SEM) are used to observe the microstructure variation, corrosion surface and fracture surface of alloys.
β phase will precipitate continuously on grain boundary in alloys annealed below 200℃. The continuous precipitation on grain boundary offered a continuous path for corrosion and lead to the severe intergranular corrosion. β phase was prone to precipitate continuously along grain boundary during the sensitization treatment and made the alloys sensitive to intergranular corrosion. Precipitation on grain boundary was discontinuous in alloy annealed at 250℃. The discontinuous precipitation on grain boundary could hindered the spread of corrosion and lead to the good resistance to corrosion.
After the sensitization treatment, H15 and alloys annealed below 200℃ were sensitive to stress corrosion due to the poor resistance to corrosion. The sensitized, 250℃ -annealed alloy exhibited a great resistance to stress corrosion due to the great resistance to corrosion.
Alloys annealed above 300℃ exhibited a poor resistance to intergranular corrosion after the sensitization, but great resistance to stress corrosion due to the low strength which made the propagation of stress corrosion cracking harder.

並列關鍵字

stress corrosion ； AA5083 Al-Mg Alloy ； intergranular corrosion ； β phase (Mg2Al3).

參考文獻

[ASTM 2] ASTM G67-04 Standard Test Method for Determining the Susceptibility to Intergranular Corrosion of 5XXX Series Aluminum Alloys by Mass Loss After Exposure to Nitric Acid (NAMLT Test).

[ASTM5]ASTM E112-10 Standard Test Methods for Determining Average Grain Size.

[BHA] N.R.M.R. BHARGAVA, I. SAMAJDAR, S. RANGANATHAN, and M.K. SURAPPA, “Role of Cold Work and SiC Reinforcements on the β''/β Precipitation in Al-10 pct Mg Alloy,” METALLURGICAL AND MATERIALS TRANSACTIONS A, vol. 29A, pp.2835–2842.(1998)

[CAL1] William D. Callister,“Materials science and engineering: an introduction 7th ed.,”WILEY,p.197.(2007)

[CAL2] William D. Callister,“Materials science and engineering: an introduction 7th ed.,”WILEY,p.174.(2007)