Effect Of Low Frequency Electromagnetic Casting With Dual Coil On The Microstructure And Mechanical Properties Of 6005A Alloy

With the rapid development of economy in our country and the increasing mileage of high-speed railway,we put forward higher requirements on the performance of highspeed train aluminum alloy.6005A aluminum alloy has better extrusion and comprehensive performance which is an ideal material for making large plate in rail vehicles.In this thesis,the possibility of the oxide films and boride as nucleation point in the aluminum alloy melt was investigated in the 6005A alloy.Simultaneously,dual-coil low-frequency magnetic casting devices are introduced in this study to improve the quality of ingot.The low-frequency alternating current is applied to the coil(A),the oxide film and boride are broken by the strong shear in the draft tube.When the coil(B)applies the low-frequency current,the melt is stirred.When two magnetic fields are used together,the crushed oxide film and boride can be uniformly distributed in the melt during casting.The paper is divided into two groups which include refiner and without refiner.The effects of dual-coil low frequency electromagnetic casting on the microstructure and properties of 6005A aluminum alloy were studied.This paper draws the following conclusions:(1)In the molten aluminum alloy with high-pressure filtration method,Al2O3 and TiB2 present lamellar and lath respectively.TiB2 particles tend to aggregate,easily combined with Al2O3 and forming inclusions.Al2O3 and TiB2 have a matching bitwise relationship with ?-Al matrix,it can be used as a substrate for nucleation of molten aluminum,thus promoting heterogeneous nucleation and refining grain.(2)After homogenized at 560? for 24h,the as-cast alloy was dissolved into the matrix and the microstructure was uniform.560?×24h is the most suitable uniform system.(3)Without refining agent,the alloy 6005A with low frequency magnetic field has a better surface quality compared with alloy without magnetic field,and its grains are also significantly refined,tissues are more uniform.After aging at 175? and maintain 12h,the yield strength and ultimate tensile strength of the alloy without magnetic fields are 335.49MPa and 363.61MPa,respectively,higher than magnetic field group of alloy,increase about 3.6%and 3.5%.Total elongation of the aging sample is 18.57%and 1.2%lower than magnetic field group of alloy.Because it is difficult to weld the large crack in the core of ingot during extrusion.Resulting in a little lower strength of the magnetic field combination of alloy after aging(4)After applying refining agent,the grain size of added magnetic alloy is 105?m,9.5%finer than the alloy without magnetic field.The surface of magnetic field alloy ingot is better and has a finer micro-structure.After aging at 175? and maintain 12h,the yield strength,tensile strength and elongation at break of the magnetic field alloyed group were 317.88MPa,348.88Mpa and 19.97%respectively,which were 15.5%,12.1%and 13.1%higher than the alloy without magnetic field.With low frequency magnetic field,the strength and plastic properties of aluminum alloy can be improved after aging.