| Aluminum-lithium 2195 alloy plate is the material used in the space shuttle fuel tanks. The plates in the tanks are joined by a welding process called Variable Polarity Plasma Arc, or VPPA. The overall mechanical properties of the structure are limited by the ductility of the welds. The mechanical properties and microstructure of the welds are influenced by many factors such as welding parameters, filler metal, welding geometry, etc.; Using hot stage optical microscopy (HSOM), this investigation studied the defect formation characteristics of Al-Li 2195 VPPA welds with Al-Si 4043 filler wire. It describes the effect of weld defects such as solid-state microcrack initiation, and also the effect of heat treatments and temperature on the dynamics of microcrack formation in the welds.; Scanning electron microscopy (SEM), and regular optical microscopy were also used to examine the surface microstructure and morphology of the welds under different conditions. In order to investigate the fracture mechanisms, some samples were pulled in tension. The examinations of the fracture surfaces revealed that the fracture of the Al-Li 2195 alloy VPPA weld is related to the amount of interdendritic ruptures and accompanying intergranular microcracks in the fusion zone. |
