(中南大学 材料科学与工程学院，长沙 410083)
摘 要: 通过拉伸试验及平面应变断裂韧性测试，研究不同时效制度对2A97合金强韧性的影响，并利用透射电镜和扫描电镜对合金的微观组织及断口形貌进行观察。结果表明：2A97合金在135 ℃单级时效时断裂韧性较好，但强度偏低；双级时效可促进强度的提高,但第二级时效温度过高时(175 ℃)，断裂韧性迅速下降，经过(135 ℃, 36 h)+(150 ℃, 18 h)时效，可得到较好的强韧性匹配，其σb、σ0.2和KIC 分别为547 MPa、489 MPa和28.9 MPa·m1/2。2A97合金中的主要强化相为δ ′相和T1相。δ ′相易共面滑移而引起应力集中，对合金韧性不利；T1相能有效地阻止位错滑移,对合金强度有显著提高。2A97合金在时效初期以穿晶和沿晶混合型断裂为主，断口表现出明显的分层特征，具有较好的韧性；随时效时间的延长，析出相的体积分数、尺寸以及临界分切应力增大，所造成的应力集中更明显，同时晶界平衡相增多，晶界无沉淀带加宽，沿晶断裂比例增多，合金韧性急剧下降。
关键字:
fracture toughness of 2A97 aluminum-lithium alloy
（School of Materials Science and Engineering, Central South University, Changsha 410083, China）
Abstract:The effect of ageing treatment on the strength and fracture toughness of 2A97 alloy was investigated by tensile test and plane-strain fracture toughness experiments. The microstructures and fracture morphologies were observed and analyzed by TEM and SEM. The results indicate that the 2A97 alloy obtains a preferable fracture toughness of in single aging at 135 ℃，but its strength is relatively low. The duplex aging enhances the strength, while the fracture toughness deteriorates at an excessive temperature as 175 ℃. The 2A97 alloy can obtain the superior combination of the strength and toughness after (135 ℃, 36 h)+(150 ℃, 18 h) aging treatment, with the σb, σ0.2and KIC of 547 MPa, 489 MPa and 28.9 MPa·m1/2, respectively. The δ′ and T1 phases are the major precipitates in the 2A97 alloy. The δ′ phase may induce the stress localization and thus deteriorate the toughness, while the T1 phase can resist the slip of dislocation effectively and significantly enhance the strength. At the early stage, it primarily presents a hybrid of transgranular and intergranular fractures with obvious delamination crackings at the fracture surfaces, which indicates a high level of toughness. The volume fraction, size and critical resolved shear stress of precipitations increase with prolonging the aging time, and lead to more severe stress localizations. In additions, the more equilibrium phases at grain boundaries, the wider PFZs together with the greater proportional of intergranular fractures result in a sharply reduce of fracture toughness.
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