Effect of Wire-Arc Additive Manufacturing Thermal Cycles on Microstructural and Properties of Al-Zn-Mg-Cu Alloy

Abstract

Al-Zn-Mg-Cu alloy has special significance for aerospace applications, and wire-arc additive manufacturing (WAAM) provides a way to produce large-scale metal structures. However, research on the effects of WAAM thermal cycles on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy is still lacking. This research focused on understanding the effects of thermal cycles on microstructure evolution and mechanical behavior of the as-deposited parts. Results indicated that the parts mainly contained microcracks (predominantly liquation cracks), interdendritic porosity, and interdendritic crystalline phase, which decreased the tensile properties. The grain morphology was dominated by the orientations reached ~65° to the deposition direction, which led to higher tensile properties in the longitudinal direction than in the transverse direction. In addition, the thermal cycles affected the softening behavior in the lower parts, and dominated the size and type of the hardening precipitates. The continuous high temperature during WAAM thermal cycles provided the strong driving force for dynamic precipitation, resulting in an over-aging forming η′ and coarse η phase in the lower part.

Keywords: Wire-arc additive manufacturing, Microstructure, Al-Zn-Mg-Cu alloy, Thermal cycle