Research On Microstructure And Mechanical Properties Of AlSi9Cu1 Matrix Composites Reinforced By In-situ Nano ZrB₂ And TiB₂ Particles

In this paper,in-situ reaction technology was used to prepare TiB₂ and ZrB₂ particles reinforced AlSi9Cu1 composites via Al-K₂TiF₆-K₂ZrF₆-KBF₄ reaction system.Microstructure and mechanical properties of different particle mass fraction?TiB₂+ZrB₂?/AlSi9Cu1 composites were studied through optical microscope?OM?,X-ray diffractometer?XRD?,scanning electron microscope?SEM?and electronic universal material testing machine analyzing.The optimum particle content of the composite was obtained.Taking the best particle content composite material as the research object,the best heat treatment process of composite is determined through the selection of heat treatment process parameters.At the same time,the elevated temperature properties of composites at different temperatures before and after heat treatment were also studied.The study showed that TiB₂ and ZrB₂ particles reinforced AlSi9Cu1 composites have been successfully prepared via the Al-K₂TiF₆-K₂ZrF₆-KBF₄ reaction system.The particle size was in range of 10¹50 nm,the particle morphology is square or hexagonal.When the mass fraction of?TiB₂+ZrB₂?is 3 wt.%,the composite got the best mechanical property and the tensile strength is226 MPa,12.87%higher than the tensile strength of AlSi9Cu1 alloy,but the plasticity of the material decreased.The influence of particles on the PLC effect in the composites is that the overall trend of the critical strain increases with the increase of particle mass fraction.As the particle mass fraction increases to 5 wt.%,the PLC phenomenon disappears.The effect of strain rate on the critical strain of AlSi9Cu1 alloy and composite material showed that the critical strain of matrix alloy decreases rapidly in the range of 1.39×10^-4s^-13.33×10^-3s^-1.When the strain rate is higher than 3.33×10^-3s^-1,the critical strain begins to increase with the increase of strain rate,which is the normal critical strain behavior.When the strain rate is lower than 5.56×10^-4s^-1,the critical strain of 3 wt.%?TiB₂+ZrB₂?/AlSi9Cu1 composite decreases with the increase of strain rate,which is opposite to phenomenon of matrix alloy.When the strain rate is higher than 5.56×10^-4s^-1,the strain rate dependence of the critical strain of 3 wt.%?TiB₂+ZrB₂?/AlSi9Cu1 composite and AlSi9Cu1alloy share the same laws.The hardness analysis of 3 wt.%?TiB₂+ZrB₂?/AlSi9CuX?X=0.8,1,1.2,1.5?composite after solid solution treatment with different temperature and time shows that the highest hardness was obtained after 6 h solid solution treatment under 510?.The size of eutectic silicon decreases with the increase of solid solution temperature.Under 510?,the average size range of the eutectic silicon is 4.5⁶.8?m,the morphology of eutectic silicon is short rod like or spherical,and the spheroidizing effect is obvious.The optimum solution parameter is 510?×6 h.At the aging temperature 170?,the strength of the composite firstly increased with the increasing of aging time,and then a small platform appeared.When the aging time is 6 h,the strength of the composite reaches the maximum value,and the best aging parameter is 170?×6 h.After heat treatment,the mechanical properties of the material have been greatly improved.The tensile strength of 3 wt.%?TiB₂+ZrB₂?/AlSi9CuX?X=0.8,1,1.2,1.5?composites increased from as-cast 180 MPa,220 MPa,232 MPa,242 MPa to 220 MPa,281 MPa,291 MPa,302 MPa,respectively,and the increasement was 22%,27%,25%,24.7%respectively.The results of elevated temperature mechanical properties show that the tensile strength of the matrix AlSi9Cu1 alloy and 3 wt.%?TiB₂+ZrB₂?/AlSi9Cu1 composites decreased with the increaseing of temperature,and the strain increased.When the temperature is higher than 200?,the softening effect of the material is obvious,and the strengthening of the particles was weakened.The tensile strength of the composite was 20%higher than that of the matrix alloy,while the strain is 40%lower that that of matrix alloy.The influence of copper content on mechanical properties of composites is obvious.When the tensile temperature is 250?and the copper content is 1.5wt.%,the tensile strength of 3 wt.%?TiB₂+ZrB₂?/AlSi9Cu1.5 composites is the highest,which is164 MPa.The fracture mechanism of the composite is ductile fracture.