The Design,Microstructure And Mechanical Properties Of Die Casting AM50 Magnesium Alloy Automobile Seat Frame

At present,the seat frame is mainly made of stamped and welded steel.However,with the lightweight requirement to the vehicle seat,thermoplastic frame,magnesium alloy frame and carbon fiber reinforced composite frame,etc.have become the main direction of the automobile seat frame's future development.Thermoplastic frame has the advantage of low cost,but its mechanical capacity and recycle ability is too low.Fiber reinforced composite frame has very good performance in mechanical capacity,but the price is too high and it is not recyclable.The cost of magnesium alloy frame is intermediate,and the seat frame possesses excellent mechanical capacity,and it is recyclable.With magnesium alloy frame,integrateddesigning can be accomplished through casting technique,then it is become a new direction of materials for seat frame.Based on the lightweight requirement and technological feasibility,a front seat made by die casting AM50 magnesium alloy is designed for a domestic type of the passenger vehicle in this thesis,which can replace the stamped and welded steel structures.Firstly,the high-pressure die casting is used toproduce the magnesium alloy frame,aiming to accomplish the complicated modeling,reduce the weight of the seat frame,and guarantee the frame's original intensity and hardness.Secondly,based on the force bearing status of the seat frame in daily running,collision,and the structure assessment of the seat frame designing,the test samples are cut from different parts of the seat frame,the metallographic analysis,the tensile mechanical test,and the fracture surfaces are observed by SEM are performed on different locations of the seat frame,through all of this,we found that different samples have different microstructure and mechanical properties,and then discussed the reason of it.Thirdly,based on the analysis result,the structure of the AM50 magnesium alloy seat frame structure and related molds are redesigned,corresponding technical design is optimized,and qualified magnesium alloy seat frame structure can be manufactured,technical support to the structural design and optimization of the die casting magnesium alloy components of seat frame could be achieved.The main research results of the thesis are as follows:(1)Through the integration of design,simulation and technology,structure optimization and integrated designing,the AM50 magnesium alloy seat frame are accomplished,which can replace the stamped and welded steel frame.(2)The seat frame employee AM50 magnesium alloywith one molding of thehighpressure die casting,reduced the number of related spare parts,promoted the overall precision,simplified the assembling process of the seat frame.Meanwhile,without the use of welding process,welding joint tearing is eliminated,and much processing time is saved.Furthermore,casting parts can have more degree of freedom,therefore,complicated molding is achievable,and the weight of the seat frame can be reduced.The final weight of all casting parts of the seat frame structure are: the quality of basin frame is 922 g,the quality of two side fenders frame are respectively 423 g and 407 g,the quality of the backrest frame is 1476 g,with 49.6% weight reduction of the seat frame.(3)Based on the bearing force status of the seat in daily running and collision,the structure assessment of the seat designing,the casting technique and performance analysis of the parts,we took samples from different parts of the seat frame,analyzed the microstructural structure and the fracture surfaces respectively by optical microscope and SEM,studied the AM50 magnesium alloy crystal size from different parts of the seat fame with Image Pro Plus software after compression molding,tested and analyzed about the mechanical properties from different parts,discovered that different samples have different microstructure and mechanical properties,and then founded out specific reason for them.For one thing,the structure of the seat frame is complex and the wall thickness is uneven,then it result in the cooling rate of the magnesium alloy liquid in different areas of casting is different,and the grain size of different area is different.For another,in the process of high pressure casting,the filling sequence of molten magnesium alloy in different parts of the mold is different,which makes the solidification sequence of the magnesium alloy liquid is different,then leading to different samples have different microstructure and mechanical properties.The results of this study show that using high pressure casting process to produce magnesium alloy seat frame,the design of the seat's die-casting die optimization must be combined with the force analysis of the casting,to ensure the property of the seat frame to meet the requirements.