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

Abstract

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 (Fp ), or tensile strength, can be as high as 85–90%, the joint efficiency for the fracture absorption energy (Et ) 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 Et but only minor variation in Fp . 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.