| Modern cars are moving toward lightweight,high speed,safe and comfortable,low cost and energy saving.Aluminum and its alloy processing materials are the ideal materials for achieving lightweight automotive products due to their low density and high specific strength.Thin-walled aluminum alloy castings have a broad application prospect in automobile body and chassis structural parts due to their good lightweight effect and excellent mechanical properties.In this paper,the car back bearing beam of die-casting AlSi10MnMg aluminum alloy was taken as the research object.The microstructure and properties of various alloys which have different heat treatment process were tested and analyzed by metallographic microscopy,scanning electron microscopy,differential thermal analysis and mechanical property test.Research indicates:(1)The effects curve of solid solution temperature and solid solution time on the tensile strength and hardness of the alloy increased first and then decreased.The effect curve of solid solution temperature and solid solution time on the elongation of the alloy first decreased and then increased.As the solid solution progresses,the eutectic silicon particles at the grain boundary gradually melt and spheroidize,and the fracture morphology of the alloy changes from mixed fracture to brittle fracture.The optimum solid solution parameter is 520?,2 h,at this time,the tensile strength is 257.0 MPa,the hardness is 96.0 HV,and the elongation is 4%.(2)The single-stage aging process of the alloy was studied.The effects curve of aging temperature and time on the tensile strength and hardness of the alloy increased first and then decreased.The effect curve of aging temperature and time on the elongation of the alloy decreased first and then increased.The peak aging was achieved at 180 ? for 3 h.At this time,the tensile strength of the alloy was 321.5 MPa,the hardness was 124.6 HV,and the elongation was 2%.The fracture of the alloy was mixed fracture.As the aging progresses,the precipitation of the second phase particles gradually increases and dispersively distributed at the grain boundaries(3)The effect of bipolar aging on the microstructure and properties of the alloy was studied by orthogonal experiment.The effect of the two-stage aging process parameters on the tensile strength of the alloy was as follows:first-order aging temperature>secondary aging time>first aging time>secondary aging temperature;the degree of influence on hardness is:secondary aging temperature>first aging temperature>secondary aging time>first aging time;the degree of influence on alloy elongation is:secondary aging temperature>secondary aging Time>first aging temperature>first aging time.When considering the strength requirements of the alloy,the optimum process parameters are 120 ?,0.5 h+170 ?,2.5 h;the final tensile strength is 326 MPa,the macro Vickers hardness is 128,and the elongation is 2.1%.When considering the plasticity and toughness of the alloy,the optimum process parameters are 120?,0.5 h+ 160?,2 h,tensile strength is 280 MPa,macro Vickers hardness is 125,and elongation is 4.6%.(4)The influence of DC electromagnetic field on the heat treatment of AlSi10MnMg alloy is investigated.Under the magnetic field,the degree of remelting of eutectic silicon particles decreases with the increase of magnetic field strength.The silicon particles increase with the increase of magnetic field strength,and DC electromagnetic field suppression The diffusion of Si atoms.The hardness value of the alloy decreases with the increase of the strength of the DC electromagnetic field.When the magnetic field strength increases from 0T to 6T,the alloy strength decreases from 50.77 HV to 46.53 HV,which is 8.4%. |
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