The Quench Sensitivity Of SiCp/2024Al Composite Based On The Jominy End Quench Test

SiCp/Al composites is one of the most competitive metal matrix composites inthe aerospace and other high-tech fields, after the heat treatment performance can befurther improved. The hardenability control is the key for the preparation of large-sized high performance SiCp/Al composites. The hardenability of high volumefraction composites is rarely reported. Therefore the research of SiCp/2024Alcomposites hardenability can provide experimental data and theoretical basis for theenactment of the actual production process of large-size high-performancecomposite.In this paper, by using transmission electron microscopy (TEM), differentialscanning calorimetry analysis (DSC), XRD, hardness test, tensile properties test,properties of as-quenched and as-aged under different cooling rates wereinvestigated. Meanwhile, in order to obtain approximate one-dimensional coolingprocess, Jominy End Quench test device suitable for composite materials wasestablished. Hardenability of composite materials can be evaluated by thehardenability curve. As a result, the conclusions can be gotten:The interrupted quenching experiments show that aging hardness of thecomposite declined with the temperature and holding time, isothermal treated at380℃the performance of composite materials declined most. Isothermal treated atthe entire temperature range of300℃to460℃, hardness had been reduced to90%of the maximum hardness, while the holding times are only1secend to2secends.As a result, the composite material is quenching sensitivity.As-quenched hardness and tensile strength decreased with the cooling rate of thequenching medium, while the variation of as-aged hardness is the same as quenched.The vacancy was annihilated at higher density of dislocation and the surfaces, sothat the formation of GP zone was disappeared in DSC and the cooling rate has asmaller effect on GP zone formation. The formation of intermediate precipitates(S”+θ”+S’+θ’) decreased as the cooling rate deceased and the formation ofintermediate precipitates during quenching caused less solute being available foraging, so that the as-aged hardness deceased and the cooling rate has a significanteffect on the formation of intermediate precipitates. At high cooling rate thedislocation density was so high that dislocation strenghthen will have an importantrole in composites at all cooling rate. The Jominy End Quench test measured the depths correspongding to90%ofmaximum artificial aging hardness are30mm. We can be obtained the relation ofprecipitation and cooling rate. When the quench cooling rate is23.6℃/sthehardness is the maximum.As the distance D from the quenched end increased the cooling rate continued todecreased and H involved in S”+θ”+S’+θ’ declined. Its variation with cooling rate(x) was the same as hardness. At lower cooling rate the intermediates precipitatedduring quenching and as-hardness decreased. TEM analysis results show that thevolume of composite strengthening phase (S’and θ’ phase) was affected by coolingrate, although the cooling rate has little effect on the size of precipitation, while itslong axis dimensions is about50nm and parallel arrangement.