Fracture Failure Analysis of QAl9-4 Aluminum Bronze Steering Cylinder Joint

The early fracture failure happened to the steering cylinder joint of the marine propeller made from QAl9-4 aluminum bronze after using in the water for eight months. Based on the fracture morphology, chemical composition, mechanical properties, microstructure and so on, the fracture reasons for the cylinder joint of QAl9-4 aluminum bronze were analyzed. The results show that: mechanical properties of the raw material were low, the brittleness of the alloy increased and the corrosion resistance of the alloy reduced because of the overproof Pb and Fe elements; the matrix structure segregated severely, and the crack source generated in the position of surface corrosion pitting under the action of alternating load and environmental corrosion; the stress corrosion cracking happened and finally led to the brittle fracture.