Reseach On Combined Forming Process Of Die Casting And Forging Of Structural Component Of AM60B Magnesium Alloy With Thin Wall And High Strengthening Ribs

Lightweight of structural components is paid more attention due to the requirementof light various devices. Magnesium alloy has been widely used as one light material inindustry due to low density, high specific strength and stiffness, etc. However, formingof magnesium alloy is an evidently difficult problem due to active anddifficult-to-deformation characters. Die casting and forging are very difficult to form thestructural components with thin wall and high strengthening ribs. In this research,combined forming process of die casting and forging is firstly developed to form thestructural components with thin wall and high strengthening ribs. A typical motorcyclecylinder of magnesium alloy is formed by combined forming process of die casting andforging to study the mechanical properties and microstructure and optimize the processparameters.A four-factor and four-level orthogonal experiment was established according toinjection speed, pouring temperature, mold temperature and forging force which are themost important process parameters in the forming process. The gating system, theoverflow launders and exhaust slots were designed according to the characteristics ofparts. Numerical simulation of high-speed filling process of motorcycle cylinder partswas done by using FLOW-3D software. Finally the optimal parameters including theinjection speed of2.5m/s, pouring temperature of660℃, mold temperature of220℃were successfully achieved. Some defects such as cracks, flow marks, sufficientdissatisfaction were found in the die casting parts. Furthermore, the flash was found inthe parts under some process parameters. High surface quality could be obtained in theparts formed by combined forming process of die casting and forging (CFPDCF). Andthere are no evident cracks and flow marks in the parts.Mechanical properties of the components formed by CFPDCF were measured byroom temperature tensile tests. The average ultimate tensile strength (UTS) of thecomponents formed by CFPDCF is241MPa and the average elongation is13.9%. Whilethe average ultimate tensile strength of die-casting parts is147MPa and the elongationis5.3%. Compared to die casting parts, the UTS and elongation of casting and forgingparts were increased by63.95%and162%. According to range analysis，the forgingforce and the pouring temperature have greater impact on forming process. Optimalparameters such as pouring temperature of660℃, injection speed of2.5m/s, diepreheating temperature of220℃and the forging force of4000kN.There are a large number of developed dendrites in the microstructure of the diecasting parts. The grain size is coarse. And there are a lot of cracks, pores and inclusions in the microstructure. While in the microstructure of casting-forging，the grain isrelatively small and there are cracks and holes. The results have confirmed thatCFPDCF is very feasible to form the structural components with thin wall and highstrengthening ribs. Not only complex shape but also high mechanical properties canbe obtained in the magnesium alloy components formed by CFPDCF.