Solidification cracking inhibition mechanism of 2024 Al alloy during oscillating laser-arc hybrid welding based on Zr-core-Al-shell wire

Abstract

Solidification cracking (SC) of 2024 high-strength aluminium alloy during fusion welding or additive manufacturing has been a long-term issue. In this work, crack-free weld could be obtained using a Zr-core-Al-shell wire (ZCASW filler material, a novel filler) coupled with an oscillating laser-arc hybrid welding process, and we investigated the solidification cracking susceptibility (SCS) and cracking behavior of AA2024 weld fabricated with different filler materials. The cracking inhibition mechanism of the weld fabricated with ZCASW filler material was elucidated by combined experiments and phase-field simulation. The results show that the effectiveness of filler materials in reducing the SC gradually improves in the order of ER2319 filler material < ER4043 filler material < ZCASW filler material. The main cracking (when using the ER2319 filler material) branches and the micro cracking branches interact with each other to produce cracking coalescence, which aggravates the cracking propagation. The formation of the Al3Zr phase (when using the ZCASW filler material) promotes heterogeneous nucleation of α-Al, thereby resulting in finer and equiaxed non-dendrite structures, which shortens the liquid phase channels and decreases cracking susceptibility index |dT/d(fs)1/2| (T is temperature and fs is solidification fraction) at final solidification. A higher proportion (7.65 % area fraction) of inter-dendrite phase with spherical distribution state, a shorter (8.6 mm liquid channel length) inter-dendrite phase coupled with round non-dendrite structure (6 µm dendrite size) effectively inhibit the SC. The present study can be a useful database for welding and additive manufacturing of AA2024.