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

Abstract

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 2×106, 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.

Keywords

• ultrasonic impact
• MB8 magnesium alloy
• cross joint
• fatigue property
• fracture morphology