超声冲击处理MB8镁合金十字接头的表层组织及疲劳性能

Microstructure and Fatigue Property of MB8 Magnesium Alloy Cross Welded Joints with Ultrasonic Impact

采用超声冲击方法对MB8镁合金十字接头焊趾处进行超声冲击处理,对比测试焊态及冲击处理态接头的表层组织和疲劳性能。结果表明:超声冲击处理可以在MB8镁合金焊接接头表面获得纳米晶组织。在循环寿命为2×106条件下,焊态试样的条件疲劳强度为32.07MPa,冲击处理态试样的条件疲劳强度为41.88MPa,提高了30.59%。未冲击接头疲劳断裂大多发生在焊缝缺陷处,冲击处理后的接头则发生在热影响区。超声冲击处理不仅可以大幅提高MB8镁合金十字接头的疲劳寿命,还可以改变接头疲劳断裂位置。此外,热影响区也是MB8镁合金十字接头疲劳断裂的薄弱区域,这与热影响区晶粒粗大有很大的关系。

Surface treatment was carried out on the weld toe of MB8 magnesium alloy welded joints with ultrasonic impact treatment(UIT)method.The Surface microstructure and the fatigue property of treated and as-welded MB8 magnesium alloy welded joints were investigated.The experimental results show that after ultrasonic impact treatment,nano-crystalline microstructure is obtained by UIT method.Under the condition of the cycle life of 2×10 6,the conditional fatigue limit of as-welded joints is 32.07MPa,and the conditional fatigue limit of treated joints is 41.88MPa,which is increased by 30.59%than that of as-welded.The fatigue fracture of as-welded joints occurs mostly in the defects of weld zone,and the fatigue fracture of treated joints occurs mostly in the heat-affected zone.The ultrasonic impact treatment can not only increase the fatigue life of the joints,but also can change the fracture position of the samples.In addition,the heat affected zone is also a weak area of the fatigue fracture of the MB8 magnesium alloy cross joints,which is greatly related with the coarse grains in the heat affected zone.