Thermal Expansion Behavior Of Aluminum Matrix Composites Reinforced By Ceramic With Ba_0.8Sr_0.2TiO₃

Low expansion materials are widely used in electronic packaging,heat sink materials and precision structures.Due to the valence bond structure of traditional materials,it is difficult to meet the characteristics of low expansion.In this paper,barium strontium titanate(BST)ferroelectric ceramic reinforced aluminum matrix composite was designed and prepared.The microstructure and thermophysical properties of the composite were studied.The BST ceramic reinforced aluminum matrix composite with light weight,high strength and low expansion was obtainedUsing barium strontium titanate(BST)ferroelectric ceramics as reinforcement,pure aluminum and 6061 aluminum alloy as matrix,BST/Al based composite was prepared by spark plasma sintering(SPS)and hot pressing sintering(HP).The effects of volume fraction of reinforcement phase,particle size of matrix and alloying of matrix on the phase structure,structure and properties of BST/Al matrix composite were studied.The mechanical,electrical and thermophysical properties of the composite were improved by annealing and thermal cycling.The influence mechanism of annealing and thermal cycling on the thermal mismatch stress of composite was discussedThe results show that the best preparation process of BST/Al matrix composites is sintering temperature 610?,holding 5 minutes and sintering pressure 40 MPa The interface of the sintered composite is smooth,and there are no holes,cracks and other defects.The closer the particle size of BST and Al is,the better the uniform distribution of BST isThe thermal expansion coefficient of BST/Al composite decreases with the increase of BST content.Heat treatment can adjust the bonding state and stress distribution between the matrix and the reinforced interphase interface,and then reduce the thermal expansion coefficient of the composite.The lowest thermal expansion coefficient of 50BST/(28?32)Al is 8.86 × 10-6/? in the range of 25??200? after 4 hours of vacuum annealing at 670?.With the increase of BST content in the reinforced phase,the compressive fracture strength of the sintered BST/Al composite increases first and then decreases.BST/Al composite with Al powder particle size of 1?3?m,when the BST ceramic content is 30%,the compressive fracture strength of BST/Al composite is the highest;BST/Al composite with Al powder particle size of 28?32?m,when the BST ceramic content is 40%,the compressive fracture strength of the composite is the highest.The electrical conductivity of the composites decreased with the addition of BST ceramics,and decreased with the increase of the content of BST ceramics.As a low conductivity ceramic phase,barium strontium titanate greatly increases the scattering effect of electrons in the composite.In addition,there is thermal mismatch stress in the composite,which leads to a large number of lattice distortion,which also leads to the increase of electron scattering.