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時效制度對Al–Zn?Mg合金組織和抗應力腐蝕性能的影響

Effect of aging on the microstructure and stress corrosion resistance of Al–Zn?Mg alloy

  • 摘要: 采用慢應變速率拉伸應力腐蝕、室溫拉伸、透射電鏡等檢測方法,研究傳統T5、T73時效處理,以及新型T5I4、T5I6斷續時效處理對Al–Zn?Mg合金微觀組織、室溫拉伸性能及抗應力腐蝕性能的影響。結果表明:斷續時效T5I4處理后材料抗拉強度為400.0 MPa,明顯高于傳統T5及T73態樣品,但材料抗應力腐蝕性能變差,應力腐蝕敏感系數為5.7%;而經斷續時效T5I6處理后,材料的抗拉強度為408.5 MPa,較T5I4態相比有所提升,與此同時抗應力腐蝕性能也得到明顯改善,應力腐蝕敏感系數為3.2%,該值明顯小于T5I4及T5態;T5I4態晶內析出相平均粒徑為2.0 nm,體積分數為8.8%,均明顯小于其他3種時效制度,其晶界析出相為細小且連續分布的點狀析出相;而經T5I6時效處理后晶內析出相體積分數為24.6%,明顯大于其他3種時效制度,晶內析出相平均粒徑(4.1 nm)較T5I4態有所增大,但依然小于T5、T73態,其晶界處析出相與T5I4態相比更加粗大,呈斷續分布形貌。

     

    Abstract: Controlling the balance between mechanical properties and stress corrosion resistance of Al–Zn?Mg alloys by aging tempers has long been an active focal point of research. Traditional peak-age can improve the mechanical properties, but the continuous precipitate at the grain boundary reduces the stress corrosion resistance of the alloy. While alloys in over-aged (T73) condition show good resistance to stress corrosion, their mechanical properties will drop significantly. In this paper, tensile properties, resistances to stress corrosion, and microstructures of the Al–Zn?Mg alloy, in interrupted aged (T5I4, T5I6) and traditional (T5, T73) tempers, were studied using a tensile test, a slow strain rate tensile test, and transmission electron microscopy. Results reveal that the tensile strength of T5I4 temper is 400.0 MPa, higher than that of T5,T73 tempers, while the stress corrosion resistance is clearly compromised, with index of slow strain rate testing, ISSRT, of 5.7%, significantly larger than that of the other three aging treatments. The tensile strength of the T5I6 temper increases to 408.5 MPa, and the stress corrosion resistance is also improved, to ISSRT=3.2%, significantly lower than that of T5 and T5I4 tempers. Volume fraction (8.8%) and average particle diameter (2.0 nm) of intragranular precipitates of T5I4 temper has the minimum value among the four aging treatments, and there are large numbers of fine precipitates distributed continuously at grain boundaries. In the T5I6 temper, the number of intragranular precipitates increase significantly, and the volume fraction of intragranular precipitates is 24.6%, larger than that of the other three aging treatments. In addition, the average particle diameter (4.1 nm) of the intragranular precipitates of the T5I6 temper is larger than that of the T5I4 temper, but is still smaller than that of the T5 and T73 tempers. Precipitates at the grain boundaries of the T5I6 temper are unevenly distributed, and significantly larger than those of the T5I4 temper.

     

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