Introduction: In the past three decades, additive manufacturing (AM), also known as 3D printing, has emerged as a promising technology, which allows the manufacture of complex parts by adding material layer upon layer. In comparison, with other metal-based AM technologies, gas metal arc welding-based additive manufacturing (GMAW-based AM) presents a high deposition rate and has the potential for producing medium and large metal components. To validate the technological performance of such a manufacturing process, the internal quality of manufactured parts needs to be analyzed, particularly in the cases of manufacturing the parts working in a critical load-bearing condition. Therefore, this paper aims at investigating the internal quality (i.e.,microstructures and mechanical properties) of components manufactured by the GMAW-based AM technology. Method: A gas metal arc welding robot was used to build a thin-walled component made of mild steel on a low-carbon substrate according to the AM principle. Thereafter, the specimens for observing microstructures and mechanical properties were extracted from the built thin-walled component. The microstructures of the specimen were observed by an optical microscope
the hardness was measured by a digital microhardness tester, and the tensile tests were carried out on a tensile test machine. Results: The results show that the GMAW-based AMbuilt thin-walled components possess an adequate microstructure that varies from the top to the bottom of the built component: lamellar structures with primary austenite dendrites in the upper zone
granular structure of ferrites with small regions of pearlites at grain boundaries in the middle zone, and equiaxed grains of ferrites in the lower zone. The hardness (ranged between 164±3.46 HV to 192±3.81 HV), yield strength (YS o f f set o f 0.2% ranged from 340±2 MPa to 349.67±1.53 MPa), and ultimate tensile strength (UTS ranged from 429±1 MPa to 477±2 MPa) of the GMAW-based AM-built components were comparable to those of wrought mild steel. Conclusions: The results obtained in this study demonstrate that the GMAW-based AM-built components possess adequate microstructure and good mechanical properties for real applications. This allows us to confirm the feasibility of using a conventional gas metal arc welding robot for additive manufacturing or repairing/re-manufacturing of metal components