Influence of interface structure and stress distribution on fracture and mechanical performance of STS439/Al1050/STS304 clad composite

Abstract STS439/Al1050/STS304 clad composite with high specific strength and high bending resistance was processed and its formability and interface fracture behavior of as-roll-bonded and annealed clad composite were studied. To predict the interface strength and the contact shear stress at the point of interface fracture, the finite element method (FEM) was carried out using ABAQUS. Post-roll-bonding annealing at 550 °C induced the formation of intermetallic compound layer both at STS439/Al1050 and Al1050/STS304 interfaces. Micro-voids, detrimental to the interface bonding strength, were observed after annealing at the interface between the intermetallic compounds and Al1050 due to the faster diffusion of Al in comparison to Fe. Interface separation and fracture occurred at the interface between STS439 and Al1050 irrespective of loading conditions in the annealed clad composite, resulting in the rapid load drop. The closer proximity of STS439/Al1050 to the neutral axis than the STS304/Al1050 interface induces greater shear stress and preferential interface cracking along the STS439/Al1050 interface. The contact shear stress as-rolled clad composite were predicted to be 241 MPa and 308 MPa without interface failure for conditions A (STS304 side in tension) and B (STS439 side in tension) using FEM, suggesting interface bonding strength after roll-bonding is greater than 308 MPa. The maximum contact shear stress predicted by FEM simulation at the point of interface cracking of the clad composite annealed at 550 °C for 12 h dropped appreciably to 125 MPa and 111 MPa for conditions A and B, respectively. The contact shear stresses further decreased to 85 MPa and 67 MPa for conditions A and B, respectively, with increase of annealing duration to 24 h.