Investigation On Heat-treatment And Heat Resistant Properties Of 2024Al/Gr/SiC_p Hybrid Composites

Hybrid aluminum martix composites possess excellent comprehensive propertiessince the advantages of the reinforcements are combined.Among all the hybrid composites,the aluminum matrix composites reinforced byflaky graphite and SiC particles have important application values and wide application prospectsin the field of national defence,transport vehicles productsdue to their superior tribological properties,high specific strength,excellent damping capacity and good machinability.However,few researches on the 2024Al/Gr/SiC compositesare reported.In the paper,the 2024Al/Grf/SiCP hybrid composite plates with 5vol.%~10vol.%of SiC particles and 3vol.%-6vol%of flaky graphite(Gr)are fabricated by vacuum hot pressing and hot extrusion processing,and the effect of thermal exposure and heat-treatment on the microstructure and mechanical properties are studied.The heat-treatment process of the 2024Al/Grf/SiCPhybrid composites is investigated.An optimum heat-treatment processingparamaters are determined.The 2024Al/Grf/SiCP hybrid composite plates with high density and uniformly distributedreinforcements aresuccessfully fabricated by vacuum hot pressing and hot extrusion processing.The 2024Al/Grf/SiCpcomposites and the 2024 alminum alloy have the similar age hardening curves.The peak hardness of 2024Al/Gr composites is lower than that of the 2024 aluminum alloys,while the peak hardness of 2024Al/Grf/SiCpcomposites is higher than that of the 2024 aluminum alloys.The aging precipitation is accelerated by the addition of SiC particles and flaky graphite,but the SiC particles have a more significant effect than the Gr due to a greater mismatch of the thermal expansion coefficient between SiC particles and the matrix.The peak aging time of the 2024Al/3Grf/10SiCp is 6h,about 8h shorter than the matrix.The tensile strength,yield strength and elongation ofthe 2024Al/3Grf/10SiCp are 387MPa,283MPa and 5.7%,respectively.The hybrid composites are characterized by ductile fracture,which is associated with the ductile fracture of the matrix and the tearing of the interface between the matrix and the particles.Effects of thermal exposure temperature and holding time on the micrcostructures and mechanical properties,as well as effects of the tensile testing temperature on the mechanical properties are studies.The microstructures of the 2024Al/Grf/SiCp composites have no obvious change and slight drops in strength and hardness occur with the prolonged holding time at 200? or lower temperature.A rapid drop in strength and hardness occurs as the temperature exceed 200?.The addition of flaky Gr and SiC particles is beneficial to heat resistance improvement,and the effect of SiC particles is more obvious.The tensile strength of 2024Al/Grf/SiCpdecreases gradually with the increasing testing temperature.The high temperature tensile strength at 200? of 2024A1,2024Al/3Gr and 2024Al/3Grf/10SiCp are 383MPa,377MPa and 372MP respectively.However their strength decrease rapidly at 250?or higher temperature.The 2024A1 alloy is featured with ductile fracture during high temperature tensile testing and after thermal exposure.However,the composties are charactistic of the mixed fracture mode associated with the ductile fracture of the matrix,the fracture of Gr and interface debonding between SiC particles and the matrix.