Improved strength and ductility on laser beam welded joints of 7085Al matrix nanocomposites by in-situ ZrB2 nanoparticles and Al3(Er, Zr) nanoprecipitates

Welding hot cracking, precipitates dissolution and coarsening during welding thermal cycle usually lead to the poor weldability of high-strength 7XXX series aluminum alloy. In this work, in-situ ZrB2 nanoparticles and Al-3(Er, Zr) (L1(2)) nanoprecipitates were used to synergistically optimize microstructure and enhance mechanical property of 7085Al nanocomposites laser beam welded joint (LBWJ). The results showed that ZrB2 and Al-3(Er, Zr) could effectively modify dendritic morphology of fusion zone (FZ) and refine grains to 1.78 mu m, which was beneficial to relieve welding hot cracking caused by coarse dendritic grains. Besides, ZrB2 ceramic particle and core-shell Al-3(Er, Zr) with high thermal stability would significantly compensate the deficiency of eta ' and eta precipitates during welding thermal cycle. The joint efficiency (JE) of ZrB2/7085Al-Er LBWJ reached up to 73.4%. Its ultimate tensile strength (UTS) and elongation were enhanced to 415.3 MPa and 6.8%, increased by 25.4% and 23.6% as compared to the 7085Al LBWJ. Crack deflection and crack bridging induced by ZrB2 and Al-3(Er, Zr) contributed to a ductile failure of ZrB2/7085Al-Er LBWJ. The synergetic effect of ZrB2 and Al-3(Er, Zr) on nucleation and growth of Al grains in FZ was deeply revealed, and the strengthening and toughening mechanisms of ZrB2/7085Al-Er LBWJ were discussed in detail.