Three-layered SS321/AA1050/AA5083 explosive welds: Effect of PWHT on the interface evolution and its mechanical strength

Abstract In this study, the effect of post-weld heat-treatment (PWHT) on the interface microstructure and its mechanical properties in the three-layered explosive welded (EXWed) SS321/AA1050/AA5083 joints fabricated with different stand-off distances were investigated. The welded specimens were heat-treated at 250 and 350 °C for 1000–10000 s. The microscopy studies exhibited that the AA5083/AA1050 interface was smooth and continuous in all conditions and was free of cracks since the SS321/AA1050 interface contained a reaction layer with variable thickness, having discontinuous and wavy morphology including some transverse and longitudinal cracks. As the stand-off distance increased, the SS321/AA1050 interface appearance altered from smooth to be wavier, and the average thickness of the developed reaction layer was enhanced from 4.95 to 6.7 μm. By PWHT, the thickness of the interfacial layer increased in proportion to the diffusion kinetics and reached a maximum of 18.56, and 15.02 μm for samples joined with a stand-off distance of 6.75 and 6 mm, respectively. For specimens with a stand-off of 6.75 and 6 mm, the diffusion driving energy values were 46.6 and 42.4 kJ mol−1, respectively, while the constant diffusion values were calculated to be 142.2 and 45.3 m2 s−1, respectively. For the samples with an applied distance of 6.75 mm, by increasing the treatment temperature and retention time, the average concentration of aluminum in the reaction layer increased since the concentration of iron decreased. Moreover, the compressive-shear strength was declined from 94.6 to 56.7 MPa. For the sample with a longer stand-off distance, lower shear strength reduction was examined after thermal treatment due to higher collision energy, the formation of wavy interface with larger amplitude, and greater plastic deformation, as well as, stronger mechanical interlocking.