Effect Of Thermal Cycle On Microstructure And Properties Of SiCp/Al Composite

The alternating temperature from high temperature to low temperature in space has a great influence on the material,in order to explore the reasons for the performance change of the particle reinforced metal matrix composite under the thermal cycle.In this paper,different sizes of SiCp/Al composites were prepared by high energy ball milling + powder metallurgy + hot extrusion,and the composites were subjected to hot and cold cycle treatment.The microstructures before and after treatment were analyzed by SEM and TEM.The properties of the microstructures before and after treatment were tested and compared.The ABAQUS software was used to simulate the stress distribution in the composites after the thermal cycle.The thermal stresses after the thermal cycle were analyzed.The reason for the impact of composite properties.In the present study,an Al-based composite material having SiC(particle size of 5 μm,1 μm,500 nm,40 nm)and a particle content of 10 vol.% was prepared by highenergy ball-milling powder,followed by powder metallurgy and hot extrusion.The SiC particles can be uniformly distributed inside the Al-based metal,and it is found by TEM that there are different degrees of dislocations in the metal matrix.With the gradual decrease of SiC particle size,the tensile strength of composites is gradually increased.The tensile strength of 40 nm SiCp/Al composites is 397 MPa,which is 261% higher than that of pure aluminum matrix.The extension of 40 nm SiCp/Al composites The rate of decline is relatively small.The hardness,thermal expansion coefficient and thermal conductivity of the composite material gradually decrease as the particle size decreases.The fracture mode of the composite material is to first produce the dimples,and then the dimples are connected to each other and finally fracture.When the SiC particles are different in size,they have different morphologies at the tensile fractures,and the fractures of the 40 nm SiCp/Al composites It is relatively smooth and smooth,and the dimples are small and relatively shallow.For composites with large SiC particle size,SiC particles are found at the bottom of the dimple.In this study,the composite material was subjected to hot and cold cycle treatment in the range of-120 °C to 120 °C.After the thermal cycle treatment,microcracks were generated inside the 5μm SiCp/Al composite,which led to a decrease in the mechanical properties of the composite.After 200 cycles of hot and cold cycles,the grain strength and elongation of the 40 nm SiCp/Al composites decreased by 3.3% and 31.7%,respectively,compared with those before untreated.The treatment of the thermal cycle has a greater influence on the plasticity of the composite.It was found by TEM observation that after the thermal cycle,the stress in the metal matrix was relaxed,and minute plastic deformation occurred at the interface between the reinforcing particles and the metal,and the dislocation density around the particles was relatively large.Before and after the hot and cold cycle,the fracture morphology of the composite material does not have a particularly large effect.In order to explore the stress distribution inside the composite,the geometric model of the representative volume unit is established.The Taylor dislocation enhancement theory is used to establish the geometric model considering the particle size effect.The finite element simulation of the model is carried out by ABAQUS software.The distribution of internal equivalent stress and maximum principal stress of Al-based and SiC particles under different thermal cycles and different sizes of SiC particles were analyzed.It exhibits a tensile stress on the metal substrate and a compressive stress on the particles.And with the increase of the number of cycles,the tensile stress on the metal matrix is gradually increased.Combined with the uniaxial tensile simulation of the composite material,the tensile strength of the composite material is gradually reduced.When the sizes of SiC particles are different,the distribution of equivalent stress and principal stress in the composite material is basically the same,and the maximum value is reached at the interface,forming a gradient distribution.