Preparation Of Heterostructured Al-Mg-Si-Cu Alloy Profiles And Their Microstructure And Properties Regulation

Al-Mg-Si-Cu alloy has the advantages of high specific strength,good weldability,corrosion resistance and excellent formability,and has become the preferred material for lightweight automobile bodies and high-speed train aluminum alloy bodies.With the development of the field of transportation,higher requirements have been put forward for vehicle performance.In this work,the Al-Mg-Si-Cu alloy with Ti B₂-Ti C particle modification was prepared by introducing low-content（2.3wt.%）Ti B₂-Ti C particles into the Al-Mg-Si-Cu alloy matrix.The heterostructure Al-Mg-Si-Cu alloy profiles with excellent mechanical properties were prepared by the combination of conventional hot extrusion technology,solution and aging heat treatment.The effects of particles on the microstructure of Al-Mg-Si-Cu alloy in as-cast and hot extrusion states were studied.The microstructure evolution of the alloy profiles,the formation mechanism of heterostructures and the strengthening mechanism in the process of solid solution heat treatment were emphatically discussed.At the same time,the interaction mechanism between hetero-deformation induced（HDI）strengthening and precipitation strengthening of aluminum alloy profiles with heterogeneous structure was revealed.The main conclusions are drawn as follows:（1）The as-cast structure of Al-Mg-Si-Cu alloy are effectively refined by Ti B₂-Ti C particles,which reduces the average grain size of the alloy from 74.7±0.8μm to 51.6±1.2μm.The recrystallization of grains in the process of hot extrusion is inhibited.After the particle modification,the tensile strength and yield strength of hot extruded profiles are increased from225 MPa and 105 MPa of the unparticle-modified alloy extruded profiles to 255 MPa and 148MPa,respectively,and the increases of tensile strength and yield strength are 13%and 41%,respectively,and has a favorable elongation of 12.5%.（2）Al-Mg-Si-Cu alloy profiles with heterostructure are prepared by simple extrusion-solution heat treatment process,and the proportion of coarse and fine grains in the heterostructure can be controlled by solution treatment time.The formation of the heterogeneous structure is attributed to the non-uniform distribution of the Ti B₂-Ti C particles,which have strong inhibition effects on the recrystallization in the particle-rich zone,while the grains in the particle-sparse zone are prone to recrystallization and abnormal grain growth.When the proportion of coarse/fine grains in the heterostructure is about 2:1,the mechanical properties of the solution-treated Al-Mg-Si-Cu alloy with heterogeneous structure achieved an optimal level（tensile strength is 345 MPa,yield strength is 227 MPa,and elongation is 12.0%）.Compared with the as-extruded the alloy,tensile strength and yield strength are increased by35%and 53%,respectively.（3）The aging heat treatment process of heterogeneous aluminum alloy profiles is optimized,and the synergistic strengthening of precipitation strengthening and HDI strengthening was realized by underaging heat treatment.Compared with T6 heat treatment,a stronger"strength-ductility matching"is obtained,and the strength and ductility are improved simultaneously.The tensile strength improved by 11%from 385 MPa to 426 MPa,yield strength improved by 10%from 366 MPa to 401 MPa,and elongation improved by 67%from4.8%to 8.0%.