Effects of interlayer temperature on the microstructures of wire arc additive manufactured Al-Zn-Mg-Cu alloy: Insights into texture responses and dynamic precipitation behaviors

Wire arc additive manufacturing (WAAM) has advantages in fabricating large-size high-strength aluminum due to unconcentrated heat sources and lower cooling rates. Successful practices in depositing high-strength 2000 series alloys have been reported extensively in recent years. However, research on the WAAM of ultra-highstrength 7000 series Al-Zn-Mg-Cu alloys is still in the feasibility verification stage. This study aims to clarify the complex relationship between microstructures and interlayer temperatures during WAAM in a high alloyed quaternary Al-Zn-Mg-Cu alloy. Single-pass multi-layered components were fabricated with interlayer temperatures of 100 degrees C, 200 degrees C, and 300 degrees C for microstructure characterization. A validated numerical model was used to simulate the thermal process and provide clues for mechanism analysis. Results show that higher interlayer temperatures lead to the non-uniform orientation of twin dendrites, refined grains, and increased high angle grain boundaries (HAGBs). But its effects on the phase type and chemical composition of second phases and precipitates are very limited. Rising interlayer temperatures help to accelerate the dynamic precipitation progress. In the thermal cycles of the specimens included in this work, the contribution of arc heat is vital to drive the dynamic precipitation process. In contrast, the contribution of interlayer temperature is very limited in general. However, higher interlayer temperatures do contribute more to driving the dynamic precipitation process. The non-uniform distribution of hardness was observed along the height direction of the fabricated specimens, where the evolution of hardness agrees well with the progress of dynamic precipitation.