Study On High Speed Semi Continuous Casting And Homogenizing Heat Treatment Of 6061 Aluminum Alloy With High Fe Content

6061 aluminium alloy is Al-Mg-Si alloy,which belongs to heat-treatment strengthening aluminium alloy.After heat-treatment strengthening,6061 aluminium alloy has many advantages,such as high strength,good formability,excellent welding performance and good corrosion resistance.It is widely used in modern aerospace,civil transportation and other tools.In this paper,the content of Fe element was increased on the basis of 6061 alloy,and the excellent structure of aluminum alloy ingot was obtained by increasing the casting speed of DC.Then homogenization heat treatment was carried out to study the effect of different homogenization heat treatment on the microstructures and precipitates of alloy ingots.In this paper,single-stage homogenization and double-stage homogenization are used to obtain high density uniform alpha dispersion phase,which is the basic research for subsequent thermal processing.The experimental results are as follows:(1)During DC casting,with the increase of casting speed,the alloy phase gradually becomes smaller.The average grain size of samples with different casting speed decreases from 262.11?m at low casting speed to 73.59?m at high casting speed.The grain size of the alloy is obviously refined at high casting speed.Through scanning electron microscopy analysis,a large number of sizes exist at low casting speed.With the increase of casting speed,the size of AlFeSi phase decreases and its distribution becomes more uniform,and the size of Mg2Si phase decreases with the increase of casting speed.It shows that high-speed DC casting is beneficial to the refinement of the second phase and the improvement of the microstructure of the alloy.(2)With the increase of casting speed,the distribution of alloying elements from center to edge becomes uniform in the direction of ingot radius.The content of alloying elements in different positions of grains is measured,and the distribution of alloying elements in grains is also more uniform.By calculating the relative solid solubility of elements,the relative solid solubility of main elements in alloys is improved.The results show that high speed casting can reduce segregation and increase solid solution of elements in matrix.(3)The mechanical properties test showed that the hardness,yield strength,tensile strength and elongation of the alloy increased gradually with the increase of casting speed.The maximum values of 95.5HV,117.1MPa,242.6MPa and 18.86%were achieved at 300 mm/min casting speed.(4)The effect of single-stage homogenization heat treatment on precipitated phase was studied.With the increase of holding temperature and time,the alloy structure became uniform gradually,and the heating rate had little effect on the structure;the average size of precipitated phase decreased first and then increased,the quantity density increased first and then decreased,and the increase of heating rate was beneficial to the increase of the quantity density of precipitated phase;the homogenization of 500?/8h at casting speed of 300 mm/min was beneficial to the increase of the quantity density of precipitated phase.The minimum size of micro-precipitated phase is about 22.8nm,the maximum quantity density is about 91.3?m-2,the hardness is 59.77 HV and the conductivity is 39.6%IACS under the temperature rise condition of 10?/min.(5)On the basis of single-stage homogenization,the effects of two-stage homogenization heat treatment on structure and properties were studied.With the increase of holding temperature and time,the alloy structure became more homogeneous and the precipitated phase size decreased first and then increased,while the density increased first and then decreased,and the effect of heating rate on size was also studied.When casting speed is 300mm/min,the average size of micro-precipitated phase is about 20.5nm,the maximum number density is about 95.8?m-2,the maximum hardness is 71.72HV and the conductivity is 37.8%IACS under the temperature rise condition of 10?/min.(6)Compared with the single-stage homogenization and double-stage homogenization,the average size of precipitated phase reduced by 11.2%,the quantity density increased by 5%,the hardness increased by 20%,and the conductivity decreased by 4.5%.