Interplay of laser power and pore characteristics in selective laser melting of ZK60 magnesium alloys: A study based on in-situ monitoring and image analysis

Abstract

This study offers significant insights into the multi-physics phenomena of the SLM process and the subsequent porosity characteristics of ZK60 Magnesium (Mg) alloys. High-speed in-situ monitoring was employed to visualise process signals in real-time, elucidating the dynamics of melt pools and vapour plumes under varying laser power conditions specifically between 40 W and 60 W. Detailed morphological analysis was performed using Scanning-Electron Microscopy (SEM), demonstrating a critical correlation between laser power and pore formation. Lower laser power led to increased pore coverage, whereas a denser structure was observed at higher laser power. This laser power influence on porosity was further confirmed via Optical Microscopy (OM) conducted on both top and cross-sectional surfaces of the samples. An increase in laser power resulted in a decrease in pore coverage and pore size, potentially leading to a denser printed part of Mg alloy. X-ray Computed Tomography (XCT) augmented these findings by providing a 3D volumetric representation of the sample internal structure, revealing an inverse relationship between laser power and overall pore volume. Lower laser power appeared to favour the formation of interconnected pores, while a reduction in interconnected pores and an increase in isolated pores were observed at higher power. The interplay between melt pool size, vapour plume effects, and laser power was found to significantly influence the resulting porosity, indicating a need for effective management of these factors to optimise the SLM process of Mg alloys.

Keywords

• Selective laser melting (SLM)
• Magnesium (Mg) alloys
• Biodegradable implants
• Porosity
• In-situ monitoring