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Post-Peak Cooling Rate Is Strongly Associated with Layer-Resolved Porosity Evolution in Hybrid WAAM-FSP Al 4043
Ahmed Nabil Elalem1, Mahmood Razzaghi2, Xin Wu1
1Department of Mechanical Engineering, Wayne State University, Detroit, MI 48202, USA.
Materials (Basel, Switzerland)
|July 15, 2026
Summary
Post-peak cooling rate, not peak temperature, controls porosity in wire arc additive manufacturing with friction stir processing (UAMFSP) aluminum builds. Slower cooling in upper layers leads to higher porosity, impacting void consolidation quality.
Area of Science:
- Materials Science and Engineering
- Additive Manufacturing
- Metallurgy
Background:
- Hybrid wire arc additive manufacturing with interlayer friction stir processing (UAMFSP) refines microstructures in aluminum alloys.
- Thermal parameters controlling layer-resolved defect evolution in UAMFSP remain poorly understood.
- Porosity is a critical defect affecting the mechanical properties of additively manufactured components.
Purpose of the Study:
- To investigate the influence of thermal parameters on porosity evolution in UAMFSP Al 4043 builds.
- To establish a correlative mechanistic framework identifying controlling factors for defect formation.
- To elucidate the relationship between cooling rate, peak temperature, and void consolidation quality.
Main Methods:
- Multi-scale characterization using infrared thermography, quantitative optical grain morphology analysis, and scanning electron microscopy (SEM).
- Image-based porosity quantification from calibrated SEM fields across multiple layers (L1-L3).
- Comparative analysis of thermal data (peak temperature, cooling rate) and microstructural features (porosity, grain morphology).
Main Results:
- A counterintuitive layer-dependent porosity gradient was observed, with the upper layer (L3) exhibiting significantly higher porosity (80%) and pore density (107%) than the bottom layer (L1).
- Post-peak cooling rate, not peak temperature, was identified as a plausible controlling factor for void consolidation quality, with L3 cooling slower (-12.3 °C/s) than L1 (-16.2 °C/s).
- High-magnification SEM revealed sub-micron pores co-located with Al-Si eutectic particles, suggesting void persistence near particle-matrix interfaces. Grain morphology also showed non-monotonic evolution with build height.
Conclusions:
- Post-peak cooling rate is a more significant factor than peak temperature in controlling void consolidation quality in UAMFSP builds.
- Slower cooling rates in upper layers promote prolonged high-temperature dwell and reduced plastic-flow-assisted pore closure, leading to increased porosity.
- The study presents a foundational mechanistic framework for UAMFSP, highlighting the need for controlled experiments to isolate causal relationships.
