Microstructure evolution and enhanced mechanical properties of additive manufacturing Al-Zn-Mg-Li alloy via forging and aging treatment

Abstract

Porosity defects are difficult to overcome in Al-Zn-Mg-Li alloys, despite their high potential for application in the military and aerospace industries. Multidirectional forging and aging treatment were applied to tune the microstructure and mechanical properties of wire arc additive manufacturing Al-Zn-Mg-Li alloy. The grains were elongated along the forging direction attributed to the severe extrusion stress, accompanied by a great density of equiaxed recrystallized grains. As the forging reduction expanded from 30% to 50%, the average grain size was evidently reduced from 23.1 μm to 16.9 μm. A considerable number of porosities were heat-welded during the forging deformation process. The Al2CuMg, Al7Cu2Fe, and Al5CuLi3 phases were severely fragmented and agglomerated in the form of condensed clusters. Furthermore, numerous needle-shaped Al3(Li, Mg) phases were stochastically distributed. As the forging reduction increased from 30% to 50% and the aging temperature/time increased (from 140 °C/5 h to 170 °C/10 h), the rod like η′-MgZn2 phase was obviously coarsened, which considerably deteriorated the properties. The ultimate tensile strength was dramatically increased from 386 MPa to 473 MPa when comparing the specimens with 30% and 50% forging reduction. Both the yield strength and hardness exhibited a similar trend. The elongation was greatly enhanced with a higher forging reduction. Ultimately, the aging behavior was thoroughly investigated and the relationship between the strength η′-phase and yield strength was theoretically discussed.