Optimal design, microstructures and mechanical properties of electrically-assisted extrusion of magnesium alloys micro-grooved heat pipes

Developing precision forming of magnesium alloy micro-grooved heat pipes is of great significance for improving the lightweight level of aerospace thermal management systems. In this paper, the electrically-assisted extrusion of magnesium alloy heat pipes is explored, and the effects of extrusion and electrical parameters on the forming accuracy, microstructures, and mechanical properties are studied. Finite element simulation found that electrifying the extrusion ram and preheating the extrusion cylinder could effectively ensure the billet temperature, and an extrusion window (30–60 s) could be obtained. Reducing the extrusion velocity and increasing the current could both reduce the extrusion load. Within the range of the studied parameters, the micro-grooved heat pipes are relatively fully formed. It is found that increasing the extrusion velocity and electrical parameters would increase the grain size of the magnesium alloy. While the electrical parameter increases from 0 to 300 A, the grain size increases from ∼5.9 to ∼12.6 µm, and the tensile strength and yield strength of the extruded profiles are also 20.7% and 16.8% lower than those without current. The tensile fracture surface shows that under the parameters of high extrusion velocity and high current, the fracture morphology changes from dimples and cleavage planes to large-area river patterns, and the fracture mode changes from the mixed ductile-brittle fracture to the brittle fracture. Under the extrusion parameters of 0.5 mm/s and 100 A, the extrusion load is reduced by 1.0–1.6 T, the cross-sectional filling rate is as high as 97.5%, and the size deviation of the micro-ribs (0.8 mm) is only ±5 µm. Simultaneously, under these parameters, the grain size does not significantly coarsen, and the strength and plasticity of the heat pipe increase slightly. This work provides theoretical and technical support for the development of precision forming technology of lightweight aerospace heat pipes.