| The mechanical properties of Al-Si alloys mainly depend on the morphology,size and distribution of primary Si.Therefore,controlling the primary Si has important significance for controlling the mechanical properties of Al-Si alloys.At present,the most widely used is P modification treatment in industry.However,there are large-scale AlP particle clusters in the Al-Si melt after the Al-P crystal seed alloy is added to the melt,which increases the viscosity of the melt.It incurred insufficient properties of the piston.Based on this,this paper studies the effects of three new Al-P-AlN,AI-P-AI3BC and Al-P-Al4C3 crystal seed alloys on the primary Si in piston alloy.The effects of new crystal seed alloys on the microstructure and properties of ML 174 alloy were also analyzed.The effects of AIN content in the Al-P-AlN crystal seed alloy on the Al-P crystal seed alloy and the effects of the new Al-P-AIN crystal seed alloy with different AIN content on the microstructure and properties of the A390 alloy were also analyzed.Aiming at the problem of the development of ?-Al dendrites in Al-Si alloys,the effects of AlTiC-B crystal seed alloy on the grains and mechanical properties of Al-Si alloy were also studied.The major research results of the present work are as follows:(1)Preparation of new type of Al-P rystal seed alloys and it's effect on microstructure and mechanical properties of ML174 alloyThree new Al-P-AIN,AI-P-AI3BC and Al-P-Al4C3 crystal seed alloys were prepared by adding AIN,A13BC and Al4C3 particles to Al-P alloy.The AIN particles adhere to the surroundings of AIP particles and enrich at the front of the liquid-solid interface,which inhibits the further growth of AlP particles.The Al3BC particles exist in the middle of AIP particle,tending to a large size AIP particle is decomposed into two smaller AIP particles.The Al4C3 and AIP have a good lattice matching relationship and the mismatch in only 5%,Al4C3 particle can be used as nucleation point of AIP particle,the nucleation points increase,and the size of AIP particle decreases.The size of AlP particles in traditional Al-P alloy is about 82 ?m,the size of AlP particles in three new Al-P-AlN,AI-P-AI3BC and Al-P-Al4C3 crystal seed alloy are 38 ?m,43 ?m,53?m.Compared with the traditional Al-P crystal seed alloys,the AlP particles in the new crystal seed alloys with particles are reduced to varying degrees,and the distribution of AlP particles in Al-P-AlN is optimal,the size of AlP particle was reduced from 82 ?m to 38 ?m.The effects of three new crystal seed alloy on the silicon phase adjustment and properties of ML 174 alloy were studied.Compared with the modification effect of traditional Al-P crystal seed alloy,after the modification with Al-P-AlN alloy on ML 174 alloy,the average grain size of primary Si decreased by about 21.7%,the ultimate tensile strength at room temperature increased by about 5.2%,and the elongation increased by about 55.6%.After the modification with Al-P-Al3BC alloy,the average grain size of primary Si decreased by about 13%,the difference in ultimate tensile strength at room temperature is not obvious,and the elongation increased by about 33.3%.After the modification with Al-P-Al4C3 alloy,the average grain size of primary Si decreased by about 30.4%,the ultimate tensile strength at room temperature increased by about 2.1%,and the elongation increased by about 33.3%.The modification effects of the three new crystal seed alloys on the ML 174 alloy are better than the traditional Al-P crystal seed alloy.By comparison,the new Al-P-AlN alloy have the best modification effect(2)The new type of Al-P-AlN crystal seed alloy and it's refinement behavior on A390 alloyBased on Al-P-AIN crystal seed alloy has the best modification effect on ML 174 alloy,Al-P-0.5AlN,Al-P-1AlN and Al-P-2AlN crystal seed alloys with different AIN contents were prepared.Adding AIN particles to the Al-P alloy,AIN will absorb P atoms in the melt to reduce the interface energy,it will adhere to the AlP particle after AlP is formed,and enrich at the front of the liquid-solid interface.The further growth of AIP particle is suppressed,thereby reducing the size of AIP particle.The size of AIP particles in Al-P alloy is about 82 ?m,and the size of AIP particles in Al-P-2AlN is the smallest,which reduces the size of AlP particles from 82 ?m to 22 ?m.The effects of Al-P-AlN crystal seed alloy with different AIN contents on the primary Si size and P absorption rate of A390 alloy were studied.The A390 alloy is refined by Al-P-AlN alloys with different AlN contents.When the AIN content in the Al-P-AlN alloys increases from 0 to 2%,the average grain size of primary Si in A390 alloy decreases from 41 ?m to 30 ?m,the absorption rate of P increases from 29.7%to 37%.Based on the best refinement effect of Al-P-2AlN alloy,the effect of Al-P-2AlN on the tensile properties at room temperature of A390 alloy was studied.When the addition amount of the crystal seed alloy is the same,compared with the traditional Al-P crystal seed alloy,the A390 alloy is refined by the new Al-P-2AlN alloy,which ultimate tensile strength at room temperature is increased approximately by 6.4%,the elongation increases approximately by 8.3%(3)Grain refinement behavior of AlTiC-B crystal seed alloyAiming at the problem of the development of ?-Al dendrites in Al-Si alloys,the effects of AITiC-B crystal seed alloy on the grains and mechanical properties of Al-Si alloy were also studied.In the B-doped AITiC-B crystal seed alloy,the B element is doped inside the TiC particles to form doped TiCxBy particles,which realizes the refinement of the ?-Al dendrite in the Al-Si alloy.The effects of AITiC-B crystal seed alloy addition of 0.25%,0.5%and 1%on the grain refinement of hypereutectic Al-Si alloy and the distribution of primary Si were studied.Before refinement,due to the coarse ?-Al dendrite in the structure,the growth of the primary Si is affected,and the distribution is relatively concentrated.After the refinement with AITiC-B alloy,the primary Si is obviously dispersed,indicating that ?-Al dendrite were refined,and when the addition amount of AITiC-B alloy was 0.5%,the distribution of primary Si was most uniform.The effect of adding 0.5%AITiC-B alloy on the grain refinement of hypoeutectic Al-Si alloy was studied.After adding AITiC-B alloy,the ?-Al dendrite were grately improved decrease.For example,the average grain size of ?-Al before refining is about 1310 ?m on Al-5Si alloy,and the average grain size of ?-Al after refining with 0.5%AlTiC-B alloy is about 154 ?m.The influence of 0.5%AlTiC-B alloy on the structure and properties of ML 174 alloy was studied.ML 174 alloy was refined by 0.5%AlTiC-B crystal seed alloy,the a-Al dendrite was refined,and the distribution of primary Si in the microstructure was more uniform.Before refinement,the the ultimate tensile strength at room temperature is about 325 MPa,and the elongation is 0.2%,the ultimate tensile strength at 350? high temperature is 93 MPa,and the elongation is about 12%.After adding 0.5%AlTiC-B alloy,he ultimate tensile strength at room temperature is about 355 MPa,and the elongation is about 0.25%,the ultimate tensile strength at 350? high temperature is 89 MPa,and the elongation is about 10.5%.Compared with unrefined,after the refinement of ML 1 74 alloy with 0.5%AlTiC-B crystal seed alloy,although the ultimate tensile strength and elongation at high temperature is slightly reduced,the ultimate tensile strength at room temperature is increased by 9.2%,the elongation is increased by 25%. |
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