Effects Of Copper Addition On The Microstructure And Properties Of High Pressure Solidification SiC_p/Al-20Si Composites

In this paper,Si C_P/Al-Si(-Cu)composites were prepared by high pressure solidification technology.The effects of different Cu contents(0%,2%,4%,6%)and different solidification pressures(1,2,3GPa)on the phase composition,microstructure and mechanical properties of the composites were studied.After heat treatment,the microstructure and properties of the composites after high pressure solidification and microalloying were analyzed and compared.The microstructure observation and properties analysis of Si C_P/Al-Si(-Cu)composites at different solidification pressures show that the Si C_P/Al-Si composites contain Si,Si C and Al phases at different solidification pressures(1,2,3GPa)With the increase of solidification pressure,the size of the irregular sheet primary Si phase in the matrix of the composites decreases gradually,and the primary Si phase disappears when the pressure increases to 3GPa.The content of primary?-Al phase increased gradually,and gradually changed from elliptical cell to dendritic.The eutectic Si phase changes from long strip shape to short rod shape.When Cu element is added to the composites,Al₂Cu phase appears.With the increase of solidification pressure,the content of Al₂Cu phase gradually decreases.The hardness(179.73HV_0.2),compressive strength(574.94MPa)and tensile strength(165.80MPa)of Si Cp/Al-20Si composites at 3GPa solidification pressure are increased by 37.98%,16.39%and 31.19%,respectively,compared with those at 1GPa solidification pressure.The hardness,maximum compressive strength and maximum compressive strength of Si C_P/Al-Si(-Cu)composites increase with the increase of solidification pressure,but the plastic deformation and total elongation at fracture decrease with the increase of solidification pressure.The fracture mode of the high pressure solidification composites is quasi cleavage fracture.When the solidification pressure is 1GPa,the fracture of the composites is mainly due to the interface debonding of Si C particles and the plastic fracture of Al matrix.When the solidification pressure is 3GPa,the reinforced phase particles of the composite appear secondary cracks and the large Si C particles appear self-fracture.The microstructure of Si C_P/Al-Si(-Cu)composites with the same solidification pressure is studied.When the content of Cu is less than 2%,a very small amount of eutectic Si grows up and tends to connect with each other,which improves the mechanical properties to a certain extent.The content of primary?-Al phase increased gradually and its size grew.When the Cu content reaches 4%and 6%,the size of the flaky primary Si phase increases obviously,and the eutectic Si particles are bound together and coarsened obviously.The content and size of primary?-Al phase increase,and the Al matrix is basically interconnected.At the same solidification pressure,the hardness of the composites increases with the increase of Cu content.The maximum compressive strength and maximum tensile strength first increase and then decrease with the increase of Cu content,and reach the maximum when the Cu content is 2%,but both are better than those of the composites without Cu element.The plastic deformation and total elongation at fracture of the composites decrease with the increase of Cu content.After aging at 175?×12h,the hardness and compressive strength of the composites are improved because Si phase and Al₂Cu phase are precipitated out during aging,which have small size and high strength,and play a role of diffusion strengthening on the matrix structure.