Study On Near-net-shape Hot-pressing Of Mg Extruded Preform

The present forge forming is characterized by its lengthy process, deformation non-uniformity, low material utilization ratio and high processing cost, and is therefore hard to be used to produce Mg forging parts for mass commercial application. To explore a new cost effective, high efficiency process with potential of stable offering quality products, based on a patented technique, the present study is devoted to do systematic research on"Near-net-shape Hot-pressing of Mg Extruded Preform"via experiments, numerical virtual reality and theoretical analysis.Aiming to produce tensile specimens with the technique, a preform extrusion profile with the 2D geometrical feature of the specimens was first produced. Then, the profile was sectioned, and net-shapely forged into the specimens with the required geometry and surface quality. Finally, the microstructure, tensile properties, processing quality, and processing parameters were empirically determined. Meanwhile, the technical and economic characteristics of the process are also examined in this paper.The obtained results show that, as compared with conventional forging forming process, the new process has the following characteristics:①Short and efficient: The new process replace the multiple forging followed by trimming with one shot close-die press forming, which consequently reduces the process sequence and increases the processing efficiency or productivity.②Low energy consumption: the new process reduces the multiple heating and forging in a conventional forge forming process to one-shot net-shape pressing of the extruded preform, which, in turn, largely reduces the energy consumption besides the processing simplification.③High material utilization ratio: the one-shot close-die pressing almost eliminates the need for residual material. Consequently, the material utilization ratio in press forming is as high as more than 95%, and the comprehensive material utilization ratio from extrusion to press remains more than 85%, far higher than 30～60% for the conventional forge forming process.④Uniform microstructure and properties: the employment of high deformation rate of≥16% during extrusion preforming ensure the obtainment of affine and equiaxed grains throughout the preform, which ensures a fine, equiaxial grains and the consequently good and uniform properties in the products. The results detailed above indicate that the newly developed process is obviously technically and economically advantageous as compared with the conventional forge forming process. As a summary, flow-chart of processing design for a Mg part and the optimal processing parameters of the new process were proposed as well to lay a sound base for its industrialization.The proposed flow-chart of processing design is: forged part drawing→forging numerical analysis→forging optimization→cross-section design of the extruded preform (profile)→design of extrusion die→design of casting billet.The optimized processing parameters for the new process are:The billet homogenization: heating at 400℃for 4 hours;Extrusion: deformation rate≥16%, die preheating temperature 400℃;Preform Sectioning: extruded profile sectioning for close die pressing with weight allowance less than 3%Close-die pressing: profile sections heated to 400℃for 30 minutes and, then, quickly removed into the die preheated to 400℃and forged with ram speed of 100～1000 mm/min.