Study On Preparation And Mechanical Properties Of High Silicon Aluminum Alloy Cylinder Liner Material

The micro-cultivator is one of the commonly used farming equipment in hills and mountains of southwest China.However,due to the low level of facility agriculture in China and the poor flatness of the land,various problems often arise in the internal combustion engine of micro tiller in the process of farming.Especially for the single cylinder air-cooled diesel engine commonly used in micro-tiller,due to poor heat dissipation and large changes in power output,there are often phenomena such as pulling cylinders,excessive wear,burning oil,and black smoke,which seriously restricts the use efficiency of micro-tiller.Aiming at these problems of single cylinder diesel engine of micro-cultivator,this study intends to explore a new type of lightweight,high wear-resisting,high-heat-conducting,well-matched cylinder block material and preparation method.The cylinder liner is made of Hypereutectic Al-Si alloy with relatively low cost by electromagnetic centrifugal casting with easily controlled process parameters.The separation and refinement function of the electromagnetic centrifugal composite force field is used to segregate the primary Si in the inner or outer layer of the cylinder liner to to form a gradient composite cylinder liner with high volume fraction,fine and uniform distribution of the primary Si.The high hardness and high wear resistance of the primary Si and the high thermal conductivity of the aluminum alloy are utilized to improve the wear resistance and heat dissipation of the cylinder liner and improve the performance of the single cylinder air-cooled diesel engine.To this end,the paper mainly carried out the following research and work:?1?Study of a single primary Si particle reinforced aluminum gradient composite.In this part,the Al-19Si high silicon aluminum alloy was used as the test object,and the electromagnetic field was added to the original single centrifugal casting.It is found that with the increase of magnetic field intensity,the primary Si are refined obviously,and the average size of the primary Si particles decreases from 70 micron to 37 micron.The particle distribution becomes more uniform,and the original particle adhesion phenomenon has been significantly improved.However,due to the small difference between the density of primary Si and that of liquid aluminium,the local segregation of primary Si particles is not obvious,and there are a large number of pores,slag inclusions and shrinkage holes in the inner region.?2?Study on aluminum gradient composites reinforced by primary Si and Mg₂Si particles.On the basis of the Al-19Si alloy,Al-19Si-5Mg was used as a research object,and primary Mg₂Si particles were introduced by adding Mg to the aluminum liquid.It is found that due to the addition of less dense primary Mg₂Si particles in the melt,there is a significant stratification in the radial direction of the sample,that is,the primary Si and the primary Mg₂Si are almost all accumulate in the inner layer of the cylinder liner to form gradient composites with high volume fraction in the inner layer.Moreover,by applying electromagnetic field,not only primary Si particles but also Mg₂Si particles can be refined to a certain extent.However,due to the application of electromagnetic field,the actual rotational speed of the melt in the mold decreases,the centrifugal buoyancy decreases,and the centripetal velocity of the pore and slag inclusion decreases,resulting in a large number of macroscopic defects in the inner and intermediate layers of the gradient material.The coexistence of primary particles and defects seriously weakens the properties of the reinforcing layer.?3?Study on Al gradient composites reinforced by primary Si and NiAl₃ particles.In order to avoid the shortage of primary particles aggregating into the inner layer with slag inclusions and pores,the research object of Al-15Si-6Ni was determined through experiments.It is found that due to the introduction of Ni element,a large amount of granular primary NiAl₃ with a density greater than that of aluminum liquid appears in the material.After electromagnetic centrifugal forming,the gradient composites were successfully prepared in which the primary Si and the primary NiAl₃ particles were concentrated in the outer layer,and defects such as pore,slag inclusion and shrinkage pore aggregated in the inner layer.The separation of the reinforcement layer and the defect layer was completely realized.Through the motion analysis of the primary particles,it is found that the velocity and acceleration of the primary NiAl₃ are larger than the primary Si at the same position.Driven by the primary NiAl₃ particles,a large amount of primary Si moves to the outer layer,and a small amount stays in the middle layer or segregates in the inner layer.?4?Study on mechanical properties of primary Si and NiAl₃ particles reinforced aluminium gradient composites.In order to investigate the feasibility of this outer layer particle reinforced gradient composite material as a cylinder liner material,this part has tested and analyzed its main mechanical properties.The hardness results show that the macrohardness of Al-15Si-6Ni presents a gradient decreasing trend of high outer layer and low inner layer.After the addition of the magnetic field,the macroscopic hardness of the sample is increased;when the magnetic field continues to increase,the hardness decreases.The results of friction and wear show that the outer layer of Al-15Si-6Ni has higher wear resistance than the inner layer;The outer layer wear amount is similar to that of gray cast iron,that is,the wear resistance is close to gray cast iron;At 2A,the magnetic field has the best effect on improving the wear resistance of the outer layer of the sample.The SEM results of the wear morphology show that the main wear forms of Al-15Si-6Ni are adhesive wear,abrasive wear,fatigue wear and oxidation wear.The tensile test results show that the average tensile strength of Al-15Si-6N increases with the addition of a certain magnetic field;When the magnetic field continues to increase,the tensile strength decreases.The tensile strength of some alloys has approached or even exceeded that of gray cast iron.The results of SEM and EDS of tensile fractures indicate that the fracture modes of Al-15Si-6Ni include cleavage fracture,quasi-cleavage fracture,intergranular fracture and microporous aggregation fracture.In summary,gradient composites in which the primary Si and NiAl₃ are distributed in the outer layer and the defects are distributed in the inner layer can be obtained by electromagnetic centrifugal casting of Al-15Si-6Ni material.Although the main mechanical properties of the gradient material outer layer?reinforcement layer?have reached or approached HT150,and it is feasible to be used as cylinder liner material of single cylinder diesel engine,it is still necessary to study the distribution of primary particles in the reinforcement area and the control of volume fraction.