Studies On Microstructure And Properties Of SiC/YL117 Composite Prepared By Diluting And Remelting Hot Pressing Prefabricated Block

SiC reinforced YL117 composites were prepared by means of diluting and remelting of SiC-Al hot pressing prefabricated block,and then the microstructures,mechanical properties and wear behaviors of composites were investigated in this paper.The SiC and Al were mixed uniformly by high-energy ball milling and the mixture powder was thermally pressed into the prefabricated block.In the process of melting,the hot pressing prefabricated block diluting and remelting in bottom of the YL117,The SiC/YL117 composite was prepared by stirring casting method when the molten cooled to semi-solid temperature.The better comprehensive performances of the composite were treated to T6 heat treatment.The optimized solution and aging process determining by the discussion and analysis of the heat treatment,the microstructures of the composites and mechanical properties after heat treatment were discussed.The results show that:The SiC with well-dispersion reinforced YL117 composites can be prepared by semi-solid stirring casting combined with the diluting and remelting of hot pressing prefabricated block.But when the volume fraction was 5.5%,the SiC particles were agglomerated.The grain size of the matrix alloy was refined and the size of the primary silicon gradually reduced until disappeared,the dendrite arm of eutectic silicon decreased,and the dispersed ?-Al2 Cu phase changed from the pattern to the point.With the volume fraction of SiC increasing,the microhardness,tensile strength and elongation of composites showed a trend of first increase and then decrease.The peak values than that of the matrix alloy increased by 21.7%,23.1% and 120.4%,and the fracture mechanism of YL117 alloy and SiC/YL117 composites were cleavage fracture and quasi cleavage fracture;The wear rate and coefficient of friction gradually decreased with the increase of the volume fraction of SiC.When the content of SiC was 5.5vol.%,the wear rate and friction coefficient decreased by 62.5% and 18.8% than the matrix alloy.The wear mechanism of the alloy was mainly adhesive wear,and the wear mechanism of the composites was the mixed behavior of adhesive wear and abrasive wear.With better comprehensive properties was 4.5vol.%SiC/YL117 composite,which optimized heat treatment process of T6 was 500oC×4h solution +170oC×10h aging.After the heat treatment,the size of the second phase was small and the silicon phase was transformed from the elongated needle to the semi continuous point chain.The tensile strength and elongation enabled further improved,increased by 33.4% and 128.0% than that of matrix alloy,and the fracture mechanism was quasi cleavage.