| Automobile lightweight is one of the development directions of automobile industry,and it is also an important symbol of the advanced technology of automobile manufacturers and the country.The lightweight of automobile is to reduce the weight of automobile as much as possible under the premise of ensuring the strength and safety performance of automobile,so as to improve the power performance of automobile,reduce fuel consumption and reduce exhaust pollution.Experiments show that at present,due to the need of environmental protection and energy saving,lightweight of automobile has become the trend of world automobile development.This paper is based on lightweight of steering knuckle to improve product qualification rate and reduce R&D costs.Foundry aluminium alloy steering knuckles have become a research hotspot to meet the requirements of modern automobile lightweight as well as the strength requirements under complex working conditions.In this paper,casting numerical simulation and optimization technology are introduced into the process development of cast aluminium alloy steering knuckle,which breaks away from the dependence on engineering experience and reduces the cost of research and development process.At the same time,the melting process,casting and testing methods of aluminum alloy steering knuckle raw materials were studied.The analysis is carried out by means of experiment,the results are as follows.The casting process is summarized as the physical reality of molten fluid filling–solidification.Three physical processes,namely flow,heat transfer and solidification,are used to describe the casting of aluminium alloy parts.For the fluid,the molten liquid of aluminum alloy filled into the mold cavity is simplified into incompressible fluid,the mathematical model of liquid flow process was studied,especially the turbulence model was introduced for the complexity of the cavity.For heat transfer and melt solidification,based on heat transfer theory,the heat generated by solidification transformation is embedded in the general heat conduction equation as an additional source term,several methods of dealing with separation by crystallization are discussed in depth.Through simulation experiment and analysis,the guiding value of numerical simulation for flow filling,temperature field change and crystallization of molten liquid was determined.In.depth analysis of the causes of defects.According to the structural characteristics and quality requirements of steering knuckle of castings,discusses three main aspects:the inheritance of defects in raw materials,the relationship between the filling velocity of molten liquid and the surface tension of the front liquid surface,and the temperature field condition of the mold cavity,the generation mechanism is explained.According to the objective of this study,the quality status of steering knuckle produced by the existing process is analyzed,the simulation and analysis of three defects:the air holes near the center hole,the shrinkage near the shock absorber hole and the air holes near the gate,the causes of these three main defects are discussed,the origin of the defect is clarified,in view of these reasons,the original production mode has been effectively improved by means of process optimization.The material,equipment and test scheme for steering knuckle preparation are described in detail.The test materials include raw material A356 aluminium ingot,pure Mg,smelting auxiliary materials and stripping and mold lubrication materials.The production equipment,sample preparation and corresponding testing equipment required for the test are listed,the methods of metamorphism,degassing and slag removal in smelting process are discussed.Method of strictly controlling chemical composition and detecting hydrogen content was put forward,and methods to prevent the influence of impurity elements in aluminum alloy.The composition of steering knuckle at different positions and the metallographic structure before and after modification were detected.A theoretical analysis was carried out about the solidification sequence and phases produced using Al.Si.Mg ternary phase diagram.The microstructures of materials A356were analyzed using optical microscopy,scanning electron microscopy based on the theoretical analysis.The identification of secondary phases such as Mg2Si and Si was carried out through applying the Energy Dispersive Spectrometer?EDS?.The solution heat treatment was conducted to find out the effect of the solution heat treatment on Vickers hardnesses based on the microstructural analysis.Finally,the artificial ageing heat treatments at the different temperatures were carried out to observe the microstructural changes along with the change of the artificial ageing treatment temperatures after solution heat treatment.We can also find out optimal artificial ageing temperature through above observation,which can be used to support the manufacturing process.The mechanical properties such as tensile strength,yielding strength,elongation,hardness and porosity ratio were also provided at the condition of before and after process optimization.The tests indicate that the mechanical properties were improved to some extent after the process optimization.The mechanism of improvement of the mechanical properties is that not only the several casting defects were extinguished,but also the microstructures were refined after the process optimization.The fracture surfaces after mechanical test show that the massive tiny dimples equally distributed at the whole fractured surface,which is identical to the higher mechanical properties after process optimization.Based on the above simulation and process optimization,the steering knuckle was trial.produced on the production site.High quality cast steering knuckle was obtained under the condition of controlling key nodes.The castings have good structure and qualified performance,which improves the yield of finished products,it meets the requirements of customers and achieves good economic benefits. |
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