Tensile behaviour of different pretreated alloy 718 sheets welded with electron beam welding (EBW)

The present paper investigates the tensile behaviour of alloy 718 sheets processed after electron beam welding (EBW). The alloy 718 sheets were pretreated in three conditions: as received, solution and precipitation pretreatments. Metallographic and fractographic examination on the specimens were conducted with optical microscope, scanning and transmission electron microscopes. Experimental results show that cracks propagate through all of the fusion zones during tensile test. The intermetallic laves phase, which precipitates along the fine columnar grain boundary in the fusion zone, offers a preferred crack propagation path, especially for the precipitation pretreated weld. The static ductility of precipitation-treated weld decreases significantly after EBW. This was attributed to high precipitation density of laves phase along the columnar grain boundary. Relatively high tensile strength and ductility of as-received and solution-pretreated welds can be obtained by using two sequential welding passes. The first pass is full penetration welding with high heat input, and the secondary pass uses cosmetic welding to reduce the surface undercut resulted from the first pass.