| The deformation process of SiC-PAMCs involves problems such as the stress distribution of the reinforcement,the interface bonding and the evolution of the matrix structure,which makes the deformation process more complicated.The deformation process of SiC-PAMCs involves the interface bonding between reinforcement and matrix,the evolution of matrix microstructure,and the flow of reinforcement,which makes the deformation process complicated.If the deformation parameters are not properly controlled in the deformation process,it is easy to cause material damage.Despite plenty of studies focusing on the hot deformation behavior of SiC-PAMCs,the deformation mechanism and microstructure evolution of the spray-deposited SiC-PAMCs remain unclear.The preparation of SiC particle reinforced aluminum matrix composites based on 7055 ultra-high strength aluminum alloy is expected to further expand the application of SiCp/Al composites in bearing structural parts.Therefore,considering the microstructural distinction from different deformation conditions,a comprehensive investigation on the microstructure evolution characteristics and mechanism of spray-deposited SiC-7055 Al during deformation is the key to the market application.In this study,the 17 vol.%SiCp/7055 Al composite was fabricated through the spray-deposition.Effects of deformation parameters on deformation behavior,microstructure evolution,constitutive models,fracture and strengthening mechanism were investigated by employing the scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,optical microscopy（OM）,Gleeble-3500,the x-ray diffraction（XRD）,the electron back scattering diffraction（EBSD）,split hopkinson pressure bar（SHPB）,four-column hydraulic machine and the deformation mechanism were also discussed.The main research contents and conclusions of this paper are as follows:（1）The examinations of in situ tensile and compression properties were performed on the spray-deposition 17 vol.%SiCp/7055 Al composite,as an attempt to study the damage and strengthening mechanisms.In the in-situ tensile process,the cracks first appear around the SiC particles,and with the increase of tensile strain,the cracks gradually expand along the origin,and the stress concentration will lead to the rupture of SiC particles.The interface bonding mode of the 17 vol.%SiCp/7055 Al composite was physical bonding,and SiC particles will be directly pulled out or peeled off,resulting in brittle fracture.The strengthening mechanism of the composite in this system was calculated through in-situ deformation and the strengthening mechanism of the composite.The Taylor-based nonlocal theory of plasticity can well describe the plastic deformation.（2）The microstructure of 17 vol.%SiCp/7055 Al composites is uniform and fine,and Mg Zn2 and Al2Cu Mg precipitates are formed during the deposition process.The proportion of LAGBs increased with the strain growth due to the SiC particles and accumulation of dislocations inhibited the migration of LAGBs.In the undeformed and deformed states,the fiber textures<111>parallel to ED and the polar textures{112}<111>were observed.The intensity of the textures slightly changed with increasing strain.（3）The constitutive model of spray deposited 17 vol.%SiCp/7055 Al composites at medium and low strain rates was established by quasi-static hot deformation behavior research.The model can better describe the stress-strain law of the composites under quasi-static deformation process.The thermal processing map was constructed based on DMM theory.The instability region of spray deposited 17 vol.%SiCp/7055 Al composite was concentrated in the low temperature and high strain rate region,and the instability region gradually increased with the increase of strain.The instability region is concentrated in the temperature range of 250℃-280℃,and the strain rate is 0.015 s-1-1 s-1.The best hot workability region is concentrated in the temperature range of 430℃-450℃,and the strain rate is 0.001 s-1-0.03 s-1.The deformation mechanism of the composite under quasi-static deformation parameters was determined by the thermal processing map and microstructure.The main deformation mechanism of the composite in the parameter range of 250℃-350℃ and strain rate 0.001 s-1-1 s-1 was dynamic recovery（DRV）,while the main deformation mechanism under high temperature（450℃）and low strain rate(0.001 s-1)was dynamic recrystallization（DRX）.The main deformation mechanism of the composites in the strain ranges of 400℃/0.001-1 s-1 and 450℃/0.01-1 s-1 is the DRV-DRX mixing mechanism.（4）The material perpendicular to the compression direction is not or is subject to smaller stress constraints,resulting in the rotation of SiC with the flow of the matrix.During the deformation process,the matrix will flow around the SiC particles due to the obstruction of SiC particles.The texture types of the composites are mainly affected by the deformation temperature.When the temperature is 250℃ and the strain is 0.001 s-1and 1 s-1,the texture are identified as{1 2 1}<2 1 0>,{1 1 0}<1 1 2>and{2 1 1}<1 7 4>respectively.When the temperature is 450℃ and the strain is 0.001 s-1 and 1 s-1,the texture orientations correspond to{1 1 1}<1 2 1>,{1 1 1}<1 1 2>and{3 2 2}<2 3 0>,respectively.（5）Based on the experimental data of dynamic deformation of materials,the Johnson-Cook（JC）constitutive model was fitted and improved,and the improved JC constitutive equation suitable for the materials in this study was obtained,which was more accurate in predicting the dynamic stress and strain of materials.When the modified JC model considers the strain rate hardening effect,instead of the softening effect,the modified JC model will not apply to the composites.It is therefore revealed that the composites have the joint effect of temperature softening and strain rate hardening during high-speed impact deformation.The macroscopic morphology of the composite under dynamic deformation and quasi-static deformation shows different ductility,and this different macroscopic phenomenon is caused by the inconsistent deformation mechanism of the composite under different deformation conditions.The plastic deformation of the composite under dynamic deformation conditions is caused by the slip of the slip band generated by dislocation accumulation.（6）Through the hot extrusion deformation test of the composites,the influence of extrusion on the microstructure evolution was discussed,and the microstructure evolution mechanism of extrusion deformation was obtained.The second phase particles of the composite extruded at 450℃ tended to be precipitated at the grain boundaries.The structural change of hot extrusion deformation at 450℃ was largely the DRV.However,DRX dominates at the extrusion temperature of 500℃ and a ratio of 20.At high temperature,the DRX produced,a relatively stable HAGBs were formed.The textures with{1 1 0}<1 1 1>paralleling to TD were observed in the composite extruded at 400℃ and 450℃.The main textures of the composites extruded at 500℃ were recrystallization textures{0 0 1}<1 0 0>and{1 2 4}<2 1 1>. |
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