| Aluminum alloys have the advantages of high specific strength,good plasticity and strong corrosion resistance.They are widely used in aerospace,automobiles,building materials and other fields.The solidification process and microstructure control of alloy are very important for producing high quality aluminum alloy castings.The composite treatment of aluminum alloy melt with refiner/modifier and different physical fields has attracted attention and made some achievements,but the research on the optimization and matching of the parameters of the composite treatment of aluminum alloy melt and the mechanism of composite strengthening need to be further studied.The rapid evaluation of aluminum alloy melt refinement/metamorphism treatment grade has been mainly based on thermal analysis technology,and there is still room for improvement in the accuracy and comprehensiveness of the evaluation.In this paper,the effects of rotating magnetic field,Al-5Ti-1B,Al-5Ti-0.2C,rotating magnetic field+Al-5Ti-1B,rotating magnetic field+Al-5Ti-0.2C on the microstructure and mechanical properties of Al-5Cu alloy and the effects of rotating magnetic field,Al-10 Sr,rotating magnetic field+Al-10 Sr on the microstructure and mechanical properties of Al Si7 Mg alloy were studied by quantitative comparison method.A new method for rapid evaluation of aluminum alloy refinement/modification grade with thermoelectric dual parameters is proposed.A rapid evaluation system for aluminum alloy refinement/modification grade with thermoelectric dual parameter sampling cup as the core is constructed.With Al-5Cu alloy and Al Si7 Mg alloy as the evaluation objects,the evaluation model for aluminum alloy refinement/modification grade is established.Rotating magnetic field,Al-5Ti-1B,Al-5Ti-0.2C,rotating magnetic field+Al-5Ti-1B,rotating magnetic field+Al-5Ti-0.2C treatment can significantly improve the grain refinement effect and mechanical properties of Al-5Cu alloy.When the magnetic field current is 120 A and the magnetic field frequency is 8 Hz,the average grain size of Al-5Cu alloy changes from 412.2 μm when it is not refined reduced to 173.9 μm.The solid solubility of Cu element in the alloy matrix is improved.The tensile strength and elongation are 197.3MPa and 12.6% respectively,which are 15.9% and 32.6% higher than those of the non-refined alloy.Al-5Ti-1B refiner and Al-5Ti-0.2C refiner have obvious refining effect on Al-5Cu alloy,and their mechanical properties have been improved significantly.When the addition of Al-5Ti-1B refiner is 1.0 wt.%,the average grain size of Al-5Cu alloy is 86.3 μm,and the solid solubility of Cu element in the alloy matrix is improved.The tensile strength and elongation of Al-5Cu alloy are 209.8 MPa and 13.1% respectively,which are 23.2% and 37.9% higher than those of the nonrefined alloy.When the addition of Al-5Ti-0.2C refiner is 1.0 wt.%,the average grain size of Al-5Cu alloy is 97.6 μm,the solid solubility of Cu element in the alloy matrix is improved.The tensile strength and elongation of Al-5Cu alloy are 200.5 MPa and13.5% respectively,which are 17.7% and 42.1% higher than those of the non-refined alloy.After the composite treatment of rotating magnetic field,Al-5Ti-1B refiner and Al-5Ti-0.2C refiner,the refining effect of Al-5Cu alloy is further improved,and the solid solubility of Cu element in the alloy matrix is also further improved.When the addition of Al-5Ti-1B refiner is 1.0 wt.%,the average grain size of Al-5Cu alloy decreases to 68.1 μm.The tensile strength and elongation reached 232.5 MPa and18.6%,respectively.When the addition of Al-5Ti-0.2C refiner reached 1.0 wt.%,the average grain size of Al-5Cu alloy decreased to 80.3 μm.The tensile strength and elongation reached 222.2 MPa and 15.7% respectively.After the rotating magnetic field is applied,due to the stirring effect of the magnetic field,the flow of the alloy melt is accelerated,and the latent heat of crystallization can be quickly dissipated.The rotating magnetic field acts on the alloy melt,reducing the undercooling of nucleation and reducing the nucleation work,which is conducive to enabling the refiner particles that do not meet the heterogeneous nucleation conditions to obtain heterogeneous nucleation ability,thus significantly improving the nucleation rate of the alloy melt.At the same time,due to the effect of electromagnetic force and eddy current,the core of mold wall will fall off and dendrites will be broken,which also makes an important contribution to the improvement of nucleation rate.Therefore,the grain of Al-5Cu alloy will be further refined by composite treatment.Rotating magnetic field,Al-10 Sr,rotating magnetic field+Al-10 Sr treatment can effectively improve the microstructure of Al Si7 Mg alloy,and significantly improve the mechanical properties of Al Si7 Mg alloy.When the magnetic field current is 80 A and the magnetic field frequency is 8 Hz,the average grain size of Al Si7 Mg alloy is 865.2%of that of untreated Al Si7 Mg alloy μm reduced to 326.2 μm,and the morphology and size of eutectic silicon have no obvious changes compared with the untreated alloy.The tensile strength and elongation of the alloy are increased to 170.2 MPa and 7.8%,respectively,which are increased by 13.2% and 36.8% compared with untreated alloy.Therefore,it has no obvious effect on the morphology and size of eutectic silicon.The average eutectic silicon length and average grain size of Al Si7 Mg alloy are 1.24μm and961.8 μm when the amount of Sr is 0.04 wt.%.Compared with the untreated alloy,the grain size of Al Si7 Mg alloy is increased.And the tensile strength and elongation of Alsi7 Mg alloy are increased to 188.0MPa and 14.3%,respectively.After the combined treatment with the rotating magnetic field and the Al-10 Sr modifier,the Al Si7 Mg alloy obtained a good double effect of refinement and modification.When the Sr content is0.04 wt.%,the average grain size of Al Si7 Mg alloy is 349.6 μm,the average length of eutectic silicon is 1.21 μm,and the tensile strength and elongation increased to 198.8MPa and 17.4% respectively.The magnetic field promotes the nucleation of alloy melt.And the magnetic field makes the distribution of temperature field and solute field more uniform,which destroys the preferred orientation of columnar crystals.Therefore,the grain of Al Si7 Mg alloy is refined obviously by composite treatment.The thermoelectric double parameter sampling cup is designed,which mainly includes the cup body,K-type thermocouple,double L-shaped quartz tube,sealing material,electrode and positioning hole.A rapid evaluation system of aluminum alloy refining/modification grade based on thermoelectric dual parameter sampling cup was constructed.The system mainly includes sampling cup,negative pressure unit,data acquisition and processing unit and supporting programs.The system can synchronously output double parameters of phase change heat and resistivity change in alloy solidification process for the same sample,and rapidly evaluate the refinement/modification grade of aluminum alloy according to the detection results of thermal electric double parameters.Based on the detailed discussion on the microstructure,mechanical properties and action mechanism of refining treatment on Al-5Cu alloy and modification treatment on Al Si7 Mg alloy,take Al-5Cu alloy and Al Si7 Mg alloy as evaluation objects.And the refinement/modification grade evaluation model based on temperature and resistivity parameters was established.And the evaluation accuracy of the model is 83.3% and 86.7%,respectively. |
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