Strength-ductility synergy of a laser welded 7085Al matrix nanocomposite joint: Interaction between ZrB2, Al3(Er, Zr) nanoparticles and MgZn2 precipitates

The dissolution and coarsening of precipitates during welding thermal cycle weakened mechanical properties of 7xxx Al alloy joints. In this work, ZrB2 ceramic nanoparticles and core-shell structured Al3(Er, Zr) (L12) with high thermal stability were introduced to synergistically enhance the mechanical property of laser welded 7085Al nanocomposite joint, and the interaction between ZrB2, Al3(Er, Zr) nanoparticles and MgZn2 precipitates was analyzed. The results showed that grain boundaries were covered by fine precipitates with discrete distribution under the action of ZrB2 and Al3(Er, Zr). The interface coherency of ZrB2/Al and Al3(Er, Zr)/Al was improved by introducing highly coherent MgZn2 precipitates to form coherent multi-interfaces of ZrB2/MgZn2/Al and Al3(Er, Zr)/MgZn2/Al. The ultimate tensile strength and uniform elongation of ZrB2/7085Al-Er nanocomposite joint were 678.9 MPa and 18.5 %, with a 36.6 % and 55.5 % increase as compared to 7085Al counterpart. The reinforced grain boundary can prevent strain localization here and allow the activation of high density of dislocations within grains. The higher interface coherency could effectively promote the dislocation multiplication and dislocation annihilation, relieving stress concentration at semi-coherent interface caused by dislocation pileup. Finally, the strength-ductility synergy was achieved in ZrB2/7085Al-Er nanocomposite joint by strengthening grain boundary and tailoring interface structure.