7050铝合金高强高韧低SCC敏感性时效工艺与机理研究

New Aging Technique and Mechanism of High Strength,High Toughness and Low SCC Susceptibility in 7050 Aluminum Alloy

在单级时效制度下,对7050铝合金进行了长时间人工时效处理。研究了不同时效状态下合金的微观组织与常规力学性能,并测试了合金的SCR性能。结果表明:不同温度下长时间人工时效处理后,合金的强度随时效程度的增加均发生明显变化,经过传统峰时效后合金的强度先减小后增大,出现第二峰值,且第二峰强度高于第一峰;合金断裂韧度随时效程度的增加而提高,第二峰韧度高于第一峰;应力腐蚀敏感性随时效程度增加而降低,第二峰抗应力腐蚀性能优于第一峰。135℃下,合金的双峰位较为突出,双峰值较高。第一峰位,σ0.2,σb分别为580MPa,625MPa;第二峰位,σ0.2,σb分别为590MPa,640MPa。第二峰位断裂韧度较好,KIC为39.5MPa.m1/2,SCR性能得到很大改善,临界应力强度因子KISCC为12.72 MPa.m1/2。微观组织分析表明:合金双峰状态下晶内及晶界组织都存在极大差异,第一峰基体组织为高密度GP区,晶界为连续带状η'相,第二峰基体组织以η'相为主,晶界为断续离散的粗大η相。

7050 aluminum alloy was processed by single stage long term aging treatment.The microstructure and mechanical properties of different aging states were studied.The ability of stress corrosion resistance（SCR） in 7050 aluminum alloy was tested by DCB stress corrosion testing method.The results show that the strength of 7050 aluminum alloy after single stage long term aging treatment at different temperatures changes obviously.At first it gets the conventional peak value,then the strength decreases until to the lowest point,whereafter,the strength turns to increasing and gets the second peak value,the second peak value is higher than the first one.The fracture toughness increases with the aging extent increasing,the fracture toughness of the second peak is much higher than the first one.The stress corrosion cracking（SCC） susceptibility decreases when the aging extent increasing,the SCR property of the second peak is more excellent than the first one.After long time aging treatment on 135℃,the two strength peaks are obvious,the two peak value are much higher,the first strength value is σ0.2： 580MPa,σb： 625MPa,the second strength value is σ0.2： 590MPa,σb： 640MPa.The second peak’fracture toughness is much better,KIC = 39.5MPa.m1/2,the SCR is improved much,KISCC = 12.72MPa.m1/2.The observation of microstructure indicates that intracrystalline structure and the grain boundary structure are both very different between the two peak stages.The intracrystalline structure of the first peak is high density GP zone,the continuous banding η＇phase distributes on the grain boundary.The intracrystalline structure of the second peak is mainly η＇ phase,the grain boundary structure is discrete thick η phase.