Metal repair using hybrid additive manufacturing process: A comparative study of interfacial surface roughness for improved mechanical strength

Sustainable manufacturing supports eco-conscious development by reducing waste and carbon emissions. Repair is a key sustainable end-of-life strategy, yet repairing complex geometries with traditional processes is often inefficient or infeasible. Additive manufacturing (AM), owing to its layer-wise deposition, provides an alternative approach for the fabrication and repair of complex parts. To enable AM-assisted repair, this study investigated a 5-axis hybrid laser metal deposition (LMD) process integrated with CNC machining and automatic tool change. Repair quality and performance of repaired components are critical, particularly in high-value industries such as aerospace and defense. The bimetallic interface between the aged substrate and newly deposited material largely determines the overall repair integrity and mechanical performance. However, interfacial defects are frequently observed in metal repair, which can significantly degrade the mechanical properties of the repaired components. To address this issue, prior studies primarily emphasize optimizing process parameters and thermal processing, while surface preparation largely remains a secondary machining step. The proposed study introduced the interfacial surface roughness as a key design parameter in surface preparation in order to enhance the mechanical strength of repaired components. Through experimental testing and finite element analysis, this work examined how controlled interface roughening affects stress distribution, failure location, and joint strength. Results reveal that the intentionally roughened interface significantly enhances mechanical strength, increasing average yield strength by 36.36%, ultimate tensile strength (UTS) by 64.23%, and average elongation at break increased from 17.50% to 39.00% compared with a highly smooth interface. The roughened interface effectively mitigated interfacial defects that prevented catastrophic failure at the joint during mechanical testing. These findings highlight that the interface roughness is critical in achieving high mechanical strength in metal repair applications.