Reseach On AZ91D Magnesium Alloy Motrocycle Wheel Produced By Combination Process Of Die-casting And Forging

Against this global development of vehicles'lightweighting, more attention was attached to the research and application of lightweight alloys. In recent years, the dosage of magnesium alloys for vehicles has been rising. So far as the vehicle dosage of magnesium alloys has been rising, the structural part are not well-matched, because of magnesium alloys'HCP structure and significant poor forgeability which lead to die-casting manufacture of magnesium alloy parts. Therefore, this paper suggested a forming process method of combination high productivity die-casting and high performance forging. As a typical motorcycle part, AZ91D magnesium alloy wheel has been produced to study this forming process.Based on three most important die-casting parameters, this paper set up an experimental program of 16 orthogonal tests which belonged to three factors and four levels. By the building of three-dimensional solid modeling of motorcycle wheel, this paper designed and optimized gating system. After optimized and simulated with the commercial mold flow software FLOW3D, this paper obtained the optimal combination of parameters: pouring temperature of 690℃, injection speed 4m/s, mold temperature 210℃.This experiment including two parts, common die-casting and combination of die-casting and forging, respectively, orthogonal test was done during each part. It was found that die-casting wheels had many surface defects, such as incomplete filling, cracks and cold shut; while wheels produced by the excellent formability method of combination die-casting and forging had less surface defects.The tensile tests of spoke showed that the spoke's mechanical properties have been greatly improved because of the existence of forging force. The average tensile and elongation of spokes increased by 68.6% and 108.9%, respectively, compared with die-casting spokes. What's more, the performances were supposed to increase by 88.7% and 169.4% after the T6 heat treatment.The microstructure of die-casting wheels was, mostly, consisted by dendrites with an average size of 180μm. Besides, the grain size had a large fluctuation from cross section view. The die-castings had many defects existed in die-casting wheel, such as dendritic segregation, oxide inclusions, cracks, holes and so on. By contrast, the microstructure of combination die-casting and forging wheels was, basically, composed of fine equiaxed grain with an average size of 25μm and a small fluctuation of grain size range from horizontal view. As the existence of forging force, defects and holes were welded. And oxide inclusions were refined and dispersed. This study proved that this combination of die-casting and forging process was feasible. Mechanical properties of parts produced by this forming process with high productivity were excellent, and could be further enhanced by follow-up heat treatment.