Failure analysis of low-pressure fracture of 2A14 aluminum alloy manhole flange ring-welded joint in the front bottom of the second stage combustion box of a certain rocket was carried out by means of fracture scanning,metallographic inspection,hardness test and other methods.The results show that the fracture originates from the stress concentration area of the weld toe that transitions from the remaining height of the back of the small-end manhole flange ring weld of the melon petal to the base metal,and expands and tears along the fusion line of the flange side.There are lots of welding porosity defects in the manhole flange ring back weld zone of the fracture site,and there are a large number of welding pores in the cover weld.The flow line of the matrix structure near the fusion line at flange side is distributed along the wall thickness direction,which is basically perpendicular to the flow line of the weld structure,and the junction of the two parts is the weak position.Moreover,the small end of the melon petal is on the verge of a complex structure with multiple welds at the front bottom of the secondary combustion box,and finally multiple factors cause the manhole flange ring weld to crack at low pressure.
2A14 aluminum alloystress concentrationwelding defectsflow line
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