Influence of welding parameters on microstructures and mechanical properties of electron beam welded aluminium-lithium plates

The present work focused on the welding characteristics of electron beam welding (EBW) in 8090 Al-Li plates, evaluated in terms of strength or toughness degradation in post-weld impact and bending tests with loading rates of 10³, 10^-1, and 10^-4 s^-1. The influence of welding parameters, such as welding power, welding speed, and electron beam focus position, on the post-weld microstructures, porosity, and mechanical properties were examined. Although the joint efficiency for the maximum flexure strength (F_p), or tensile strength, can be as high as 85-90%, the joint efficiency for the fracture absorption energy (E_t) was only 20-40%, a level usually unsuitable for applications. It was found that changing the welding power and speed by a factor of 3 resulted in significant variation in E_t but only minor variation in F_p. Changing the welding focus position had little effect on post-weld mechanical properties. The abundant grain boundary precipitates in the welded specimens were thought to be the main cause of the degraded post-weld properties. Other microstructural factors included the δ′ precipitate and grain sizes. The volume fraction of porosity did not play any decisive role owing to the small size (<0.3 mm), low quantity (1-2%), and spherical shape of the EBW induced pores. Finally, given the same post-weld microstructures, the toughness degradation of the EBW specimens was worst under high rate impact loading.