| The electronic control system,battery,and motor(hereinafter referred to as the EIC system),which as the core components of new energy vehicles are becoming lighter,more precision and more integrated by the rapid development of new energy vehicles.Therefore,the higher power consumption required to the structural materials is required to own the higher heat conduction.Compared with traditional steel materials,aluminum alloy has the advantages of low density,high specific strength,and good thermal conductivity which is an ideal material for the structural parts of the three-electric system of new energy vehicles.At the same time,liquid forming has become one of the important production processes of thin-walled and complex structural parts.Now,liquid forming is also becoming the new energy automobile industry because of its high dimensional accuracy,good utilization of molten metal,stable filling,and high density,especially the low-pressure casting process.Especially,The high mold filling and capacity of feeding a casting perfectly meets the manufacturing process requirements of thin-wall and complex structural parts.Firstly,according to the structural requirements of the EIC system,this article explores ways to improve its thermal conductivity and mechanical properties by adding Sm and time-effective treatment on the basis of A356 cast aluminum alloy which has a deal with Sr/B modification treatment.Secondly,based on the optimized material,the thin-walled plate sample was used as the experimental object to optimize the liquid forming metal mold and process of the casting.Lastly,the factors which affect microstructure,thermal conductivity,and mechanical properties of the optimized liquid forming performance have been studied.The main work and results are as follows:(1)Taking the as-cast Sr/B modified A356 aluminum alloy as the research object,study the influence of the Sm and low-temperature aging treatment on the alloy structure,thermal conductivity,and mechanical properties.It can also optimize the modified A356 alloy with better thermal conductivity and mechanical properties.The results show that with the gradual increase of the addition of Sm element,the mechanical properties of the alloy show a trend of first increasing and then decreasing,while the thermal conductivity shows a small decreasing trend.When the addition amount of Sm is 0.6wt.%,the as-cast Sr/B compound modified A356 aluminum alloy has the best modification effect,which grain refinement is obvious,and the tensile performance is significantly improved at the same time.The tensile strength and elongation are respectively 203.7 MPa and 8.4%.The thermal conductivity of the alloy is 159W/(m·K).The as-cast Sr/B compound modified A356 aluminum alloy is subjected to appropriate low-temperature aging treatment.It shows that the precipitated part of the alloy is solid-dissolved in the matrix.So the thermal conductivity of the as-cast Sr/B composite modified A356 aluminum alloy is increasing.Not only the tensile properties of the as-cast Sr/B composite modified A356 aluminum alloy is increasing,But also the tensile properties are decreasing slightly.When the aging treatment is 10 h,the thermal conductivity of the alloy is 196.7 W/(m·K),and the tensile strength and elongation of the alloy at this time are180.5MPa and 3.2% respectively.Compared with commercial A356 aluminum alloy,its tensile strength and thermal conductivity have been significantly improved.(2)On the basis of the previous research,using the finite element analysis method to optimize the low-pressure casting molding die and process of the A356 aluminum alloy thinwalled plate sample.What the optimal low-pressure casting process parameters obtained from the analysis are that lifting pressure is 40 k Pa,lifting speed is 50mm/s,filling pressure is 50 k Pa,filling speed is 115 mm/s,holding pressure is 70 k Pa,holding pressure boosting speed is5 k Pa/ s,the molten metal temperature is 700°C,and the mold temperature is 450°C.At the same time,using FEM to analyze the influence of gravity casting and the low-pressure casting process on the filling and solidification process of aluminum alloy thin plates.The results of the simulation analysis are as follows.During the gravity casting process,the molten aluminum is not filled smoothly and the feeding is insufficient during solidification,which is prone to defects such as trapped air and shrinkage holes;while the molten aluminum fills smoothly during the low-pressure casting process and the feeding is sufficient during solidification.After the plate is formed,the overall quality is high and the shrinkage cavity and porosity are few.(3)Based on the optimized composite processing A356 aluminum alloy composition and thin-walled plate sample forming process analysis results,What experiments were carried out are the aluminum alloy sheet gravity casting and low-pressure casting.Compare with two forming processes and their filling and solidification.We analyze its structure and performance.It shows that there is a problem of poor consistency in the gravity-casting,which ultimately results in a large difference in the position of the thin sheet and the quality of the surface casting.The qualified rate of the plate is low and the consistency of the experimental is poor.There is a big difference in the structure and performance between the closing sprue area and the far sprue area.The average grain size of the gravity cast A356 alloy sheet near the sprue and the far sprue area are 55?m and 24?m respectively.The average tensile strength is92.6MPa and 115.3MPa.The average elongation is 7.5%,13.7%.The thermal conductivity is108.3W/(m·K),124.5W/(m·K).The same tendency of the 0.1B-0.15Sr-0.6Sm-A356 alloy sheet gravity casting.The average grain sizes of the near gate and far gate regions are 65?m and 33?m respectively.The average tensile strength is 105.1MPa and 120.8MPa.The average elongation rates are 8.3% and 14.8%.The thermal conductivity is 127.8 W/(m·K)and 145.2W/(m·K).However,the surface of the low-pressure casting sheet is not only smooth but also there is no obvious defects such as entrainment,shrinkage and porosity.More importantly,the process stability is good so the structure and performance of the thin-plate parts near the sprue and far sprue area change little.The results of the low pressure casting 0.1B-0.15 The average grain size of the Sr-0.6Sm-A356 alloy sheet near the sprue and the far sprue area is 48?m and37?m respectively.The average tensile strength is 130.7MPa and 134.5MPa.The average elongation is 13.0% and 14.0%.The thermal conductivity is 129.3 W/(m·K)and 132.7W/(m·K).The overall performance of the low-pressure casting of 0.1B-0.15Sr-0.6Sm-A356 alloy sheet is lower than that of the gravity casting.The main reason is that under the experimental conditions,the crucible is unevenly mixed and the alloy has not been modified fully that the effect is not obvious. |
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