AZ31镁合金裂纹扩展各向异性声发射特征分析

Anisotropic Fatigue Cracking Behavior of AZ31 Mg Alloy Based on Acoustic Emission

利用声发射技术对AZ31镁合金轧制方向和横向的疲劳裂纹扩展行为进行了研究。结果表明,镁合金疲劳裂纹扩展过程中产生的声信号撞击数与循环载荷的关系,以及撞击数上升率和应力强度因子幅的关系d C/d N-ΔK,分别与常规疲劳裂纹扩展试验结果相一致,裂纹失稳扩展临界应力强度因子幅与常规试验结果的误差分别为2.86%(裂纹沿轧制方向)和3.00%(裂纹沿横向);载荷一定时,裂纹沿横向扩展总是比沿着轧制方向扩展更慢一些,进入失稳扩展阶段更迟。微观组织显示,裂纹沿横向扩展边缘处的孪晶明显增加,断口处也表现出更明显的塑性,这对裂纹的扩展产生了阻碍,即材料在横向的抗裂性能要优于轧制方向,同时证明了利用声发射监测裂纹扩展行为的可靠性。

Fatigue crack propagation experiment of AZ31 magnesium alloy in different directions were conducted accompanied by acoustic emission monitoring,and the results presented similarities with the conventional results.Acoustic emission hit counts have a liner relationship with the stress intensity factor range at the stable cracking stage,and the turning point of dC/dN-AK curves have errors of 2.86%(along the rolling direction)and 3.00%(vertical to the rolling direction)with that of da/dN-AK.The crack propagates along the roiling direction slower than along another direction,and the reason could be as follows:there are obvious quasi-cleavage fracture and more twins when the crack propagates vertical to the rolling direction,which could stop cracking to some extent.So the crack resistance of rolling direction is worse than that of another direction;meanwhile it is demonstrated that the acoustic emission technique is a practical method to study the fracture behavior.