超声冲击对MB8镁合金焊接接头超高周疲劳性能的影响

Effect of ultrasonic impact treatment on ultra high cycle fatigue properties of MB8 magnesium alloy welded joint

通过超声冲击试验和超声疲劳实验来探究超声冲击对MB8镁合金焊接接头超高周疲劳性能的影响。结果表明:由S-N曲线可知,在106~109寿命区间内,冲击态试样的疲劳性能要高于焊态。在应力为40 MPa载荷下,焊态试样的疲劳寿命为1.86×10~7,而冲击态试样的疲劳寿命为9.77×10~7,提高425%,说明超声冲击可以明显提高MB8镁合金焊接接头的疲劳寿命。裂纹都是萌生于焊趾区,试样的断口存在6个不同区域:疲劳源区、初始扩展区、过渡扩展区、粗晶扩展区、柱状晶扩展区、瞬断区。

The effects of ultrasonic impact treatment（UIT）on ultra high cycle fatigue properties of MB8 magnesium alloy welded joint were investigated by ultrasonic impact test and ultrasonic fatigue test. The results show that,according to the S-N curve of the fatigue life,in the 106-109 cycles range,the fatigue properties of treated specimens are higher than those of the welded specimens. Under the stress of 40 MPa,the fatigue life of welded specimen is 1.86×10~7 cycles,while the fatigue life of impact specimen is 9.77×107 cycles,increasing by 425%. This shows that UIT can significantly improve the fatigue life of welded joints of MB8 magnesium alloy. The cracks are initiated in the weld toe,and there are six different regions in the specimen fracture：the fatigue source zone,the initial expansion zone,the transition extension zone,the coarse crystal extension zone,the columnar crystal extension zone and the transient fracture zone.