Study Of TCB And AlN On The Grain Refinement And Strengthening Behavior Of Hypoeutectic Al-Si-Mg Alloys

Hypoeutectic Al-Si-Mg aluminum alloy is widely used in aerospace,transportation and other fields because of its low density,high specific strength,excellent corrosion resistance,electrical and thermal conductivity.However,the ?-Al grains in the solidified structure of the alloy are extremely coarse,and casting defects such as shrinkage porosity and "snowflakes" are likely to occur,which seriously damages the mechanical properties of the alloy.Therefore,it is imperative to fundamentally solve the problem of grain refinement of Al-Si-Mg alloys and improve the strength and toughness of materials.Based on this,in this paper,Al-TiCB master alloys(hereinafter referred to as TCB master alloys)that are resistant to Si refinement"poisoning" and Al-Si-AIN master alloys containing nano-AIN particles(abbreviated as ASN master alloys),Used in Al-Si-Mg alloy.The fine-grained high-strength and toughness Al-Si-Mg alloy is prepared by adjusting the alloy structure through the method of fine-grain strengthening and nano-particle second-phase strengthening.In addition,the Al-Si-Mg alloy is used as the matrix,and AIN and Si3N4 are the reinforcing phases,and the(AIN+Si3N4)/Al-Si-Mg composite material is synthesized in-situ to further improve the mechanical properties of the alloy.The main work of this paper is as follows:(1)Control of TCB master alloy on the solidification structure and mechanical properties of ZL114A aluminum alloyThe TCB master alloy contains a large number of dispersed,efficient and stable nucleation particles,which can play a role in resisting Si "poisoning".Therefore,this paper selects the representative grade of Al-Si-Mg alloy ZL114A as the research object.Through the introduction of TCB master alloy,the purpose of refining ?-Al grains and improving the distribution of eutectic Si is achieved,and finally the mechanical properties of the alloy are improved.The test results show that after adding 0.3%,0.6%,and 1.0%TCB master alloy to ZL114A aluminum alloy,the average grain size of ?-Al is refined from 1224?m to 186 ?m,122 ?m and 116 ?m,respectively;After heat treatment,the yield strength of the alloy was increased from 265 MPa to 295 MPa,300 MPa,and 330 MPa,respectively,which increased by 11.3%,13.2%,and 24.5%;the tensile strength was increased from 325 MPa to 347 MPa,358 MPa,and 370 MPa,respectively.,Increased by 6.8%,10.2%,and 13.8%respectively.(2)Effect of ASN master alloy on the microstructure and mechanical properties of ZL114A aluminum alloyAIN has high elastic modulus and good thermal stability.It is a high-quality reinforcing phase.It can give full play to the role of second phase particle strengthening in aluminum alloys and improve the mechanical properties of the alloy.The ASN master alloy is rich in a large number of nano-AIN particles.After 1.0%ASN master alloy is added to the ZL114A aluminum alloy,the average ?-Al grain size of the alloy is refined from 926 ?m to 245 ?m,and some The morphology of eutectic Si changed from lamellar to coral.After T6 heat treatment,the brinell hardness of the alloy was increased from 107.8 HBW to 127.4 HBW,the tensile strength and yield strength were increased from 325 MPa and 240 MPa to 390 MPa and 345 MPa,respectively,and the elongation was reduced from 12.8%to 12.0%.(3)Preparation of high strength and toughness(AlN+Si3N4)/Al-7Si-xMg alloy materialIn order to prepare new high-strength Al-Si-Mg alloy materials,the Al-Si-Mg alloy is still used as the matrix,and nano-AlN and sub-micron Si3N4 reinforcement phases are introduced.At the same time,control the content of Mg element in the alloy,and combine the extrusion deformation and heat treatment process to further optimize the structure and properties of the alloy.The test results show that increasing the content of Mg element,the brinell hardness,yield strength and tensile strength of the alloy show a trend of first increasing and then decreasing,while the elongation gradually decreases;when the content of Mg element is 1.0%,the structure and performance of the alloy are the best Good,its Brinell hardness can reach 143.8 HBW,and the yield strength,tensile strength and total elongation after fracture are 405 MPa,491 MPa,and 5.8%respectively.