The role of surface integrity and microstructure on the machinability of AZ31 Mg alloy fabricated through the CMT-WAAM process

Abstract

This investigation explores the porosity, microstructure and mechanical properties of AZ31 Mg alloy fabricated by cold metal transfer-based wire arc additive manufacturing. The X-ray computed tomography (XCT) analysis reveals an average porosity volume of 0.20% with an equivalent diameter range of 0.312–0.783 mm. The as-built part exhibited equiaxed microstructure with different average grain sizes in the built direction (BD) (62.5 ?m) and travel direction (TD) (45.3 ?m). Consequently, mechanical properties in BD and TD are different. Moreover, this study also explores the optimization of milling parameters and the effect of porosity, different grain sizes and secondary phase particles on cutting force, surface roughness, chip formation, and changes in microstructure during milling operation of as-built components. The BD shows higher cutting force with more fluctuation, higher surface roughness, less chip curliness and low microstructure influence depth than TD. EBSD results found that the TD specimens undergo continuous dynamic recrystallization (CDRX) during machining owing to higher plastic deformation and sub-grain rotation, which transforms low-angle grain boundaries (LAGBs) to high-angle grain boundaries (HAGBs), resulting in grain size reduction from 45 ?m to 5 ?m up to 25 ?m depth, which is higher than that of BD. The comparison results of the milled sample in BD and TD show that the TD direction milling (V<inf>c</inf>: 157.079 m/min, f<inf>t</inf>: 0.01 mm/tooth and d<inf>c</inf>; 1.5mm) gives more favourable outputs. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.