Research On Hot Deformation Behavior Of SiC_p/6061 Composites Prepared By Spark Plasma Sintering

Aluminum matrix composites(AMCs) have attracted considerable attention owing to its excellent comprehensive performance, such as low density, high strength, high elastic modulus, high wear resistance, high thermal conductivity and low thermal expansion coefficient, etc. The mechanical properties can be further optimized by the means of particle-reinforcing, producing the particle-reinforced AMCs which possess potential applications in aeronautics, aerospace, automotive and electronics industry. However, reduction in plasticity resulting from reinforcing induces the deterioration of its processing properties, and thus limits its practical application. Thus, appropriate and unambiguous reinforcing process parameters are highly desired to fabricate AMCs with expected comprehensive performance. This paper focus on the preparation process, and relationship between the reinforcing process parameters and mechanical properties of particle reinforced AMCs fabricated by spark plasma sintering(SPS) of ball-millinged powders. and hot processing performance as well as mechanical properties of these composites was investigatedThe morphology and microstructural features of SiC_p/6061 powders after different milling dwell time were investigated with the help of SEM and XRD. Within dwell time of 10 h, no new phase can be detected in recovered powders. The distributing of SiC_p becomes uniformity, and the grain size of 6061 powders is reduced continuously with the increase of dwell time. Meanwhile, the oxygen content in recovered powders increase along with mill time. Based on the measurements of grain size and oxygen content, the optimized milling dwell time is set to be 3h.During the SPS process, the contraction curve was recorded and used to analyze the densification process of 6061 powders. The sintering parameter was optimized and determined based on the investigations of density, microstructure and tensile properties of as-SPSed 6061 samples with different sintering temperatures. The relationship between microstructural features and tensile properties suggests that the strength and ductility of SiC_p/6061 composites are highly dependent on the volume fraction and distribution of SiC_p. The strength of SiC_p/6061 composites shows a highest value of 236 MPa with 15vol% SiC_p, but it reduces to 219 MPa when SiC_p volume fraction reached 20%.The hot deformation behaviour of SiC_p/6061 composites was further studied through isothermal and constant-strain-rate compression tests, which were conducted on a Gleeble-3500 testing system. The relationship among the flow stress of composites, the deformation temperature, and the strain rate during hot compression was explored, the hot deformation activation energy and constitutive equation were deduced by Zener-Hollomon parameters. The processing map of 10 vol. %SiC_p/6061 composites was established according to the dynamic materials model and Prasad instability criterion. The microstructure evolution and dynamic softening mechanism during hot deformation process were analyzed. The results indicate that the stress-strain curves of the SiC_p/6061 composites had a typical characteristic of dynamic softening. The flow stress decreased with the increase of deformation temperature, and also increased with the rise of strain rate and the volume fraction of SiC_p. There were two stabilization regions in the processing map of 10 vol.%SiC_p/6061 composites: 300-425℃, 0.1-0.001s-1 and 450-500℃, 1-0.1s-1, corresponding to two type of dynamic softening mechanisms, i.e., dynamic recovery and dynamic recrystallization, respectively. The optimal hot processing conditions of 10 vol.%SiC_p/6061 composites are determined to be 500℃ and strain rate 1s-1.The effects of temperature, rolling speed, reduction per pass, milling time and volume fraction on mechanical properties of SiC_p/6061 composites were studied. And the best rolling conditions were determined to be rolling temperature of 500℃, rolling speed of 0.2m/s and reduction per pass of 0.6-0.15 mm. The AMCs sheet with a thickness of ~1mm was prepared, and the microstructure and tensile properties of these AMCs were also investigated. The results suggest that the rolling process can effectively refine the grain size and improve the uniformity of reinforcement of AMCs. After rolling, the ductility and strength of composites were improved simultaneously. The strength and elongation of 20 vol.%SiC_p/6061 composites increase from 219 MPa and 0.91% to 414 MPa and 1.97%, respectively. Meanwhile, the 10 vol.%SiC_p/6061 composites sheets possess superior tensile strength and ductility to 10 vol.%TiC_p/6061 and 10vol.%Zr Cp/6061 composites sheets, which were prepared at the same conditions.