Study on hot cracking in laser welded joints of inconel 718 alloy foils

Abstract

Pulsed laser welding was used to join ultra thin Inconel 718 alloy foils whose thickness was 0.2 mm. A fixture was designed to obtain the edge joint. The joint geometry and hot cracking were both observed on the cross sections. The relationship between the height, width of the joint and the energy density were fitted as linear functions. The effect of heat input on the hot cracking in the edge joint was obtained. It was shown that a hot cracking occurred during the solidification of the molten metal under laser heating. The crack initiated at the gap between the foil pair and propagated along the Laves phase with low melting point. The crack length could be reduced by applying low heat input. Tearing tests were conducted to evaluate the influence of the cracking on the mechanical performance of edge joints. There existed two failure modes for the edge joint under a tear loading. When the crack length exceeds 106.9 μm the hot crack starts to propagate and the tear loading decreases with crack length increasing. A finite element model was established to simulate the stress evolution during the cooling stage. The main reason of crack initiation and propagation were both presented.