Research On Machining Mechanism And Surface Formation Characteristics Of Plastic Domain Based On SiCp/Al Composite

Particle reinforced SiCp/Al composites have the characteristics of high strength,small thermal deformation,wear resistance and fatigue resistance.The mismatch of mechanical properties between SiC reinforcement phase and Al matrix results in poor coordination deformation ability of SiCp/Al composites,and the complex plastic and brittle removal mechanism is presented in the machining process,which is easy to lead to machining defects.In this paper,through the nano indentation experiment and variable cutting deep scratches the experimental research of mechanical properties,such as analysis of SiCp/Al composite plastic brittle transition of critical conditions,further establish a two-phase hybrid particle random distribution and finite element simulation model of single particle cutting experiment in high speed cutting,the SiCp/Al composite material removal mechanism and the machined surface formation mechanism.Firstly,the deformation process of Al matrix and SiC particles under different loads are analyzed by nanoindentation experiments.The in-situ mechanical properties of Al matrix and SiC particles are obtained by constructing the load displacement curve,and the criterion and critical condition of plastic brittle transition of SiC particles are determined.The results show that the coordinated deformation mechanism of each phase in SiCp/Al composites is significant,in which the elastic modulus of Al matrix phase is higher than that of homogeneous aluminum alloy,and the elastic modulus of SiC particle reinforced phase is lower than that of homogeneous SiC material.The critical depth of plastic-brittle transition of SiC particles is not a fixed value,but the range affected by the loading rate,which is about55?120nm.Secondly,the mechanism of removal of SiCp/Al composite under different cutting depth and loading speed was analyzed by means of scratch test.The results show that the friction coefficient first increases,then decreases and finally increases with the increase of cutting depth,which reveals the processing law of plastic-brittle transformation of SiCp/Al composites.With the increase of cutting depth,the scratch has the deformation mechanism of substrate coating interface cracking particle breakage.With the increase of feed speed,the mechanism of scratch removal presents a plastic-brittle transition from matrix smearing to interface cracking to reinforcement crushing.With the increase of loading speed,the radial cracks and shallow pits on the scratch surface decrease.Then,based on the two-phase mixed particle random distribution model,the simulation analysis of the cutting process of SiCp/Al composites was carried out.Combined with the scratch morphology,the formation mechanism of interface cracking,particle flying out and pressing in the process of cutting removal of SiCp/Al composites was revealed.Based on the single-particle model,the parameters of the cutting path with different positions of the tool relative to the particle were obtained,and the particle removal mechanism was analyzed.The influence of cutting speed on surface defect formation is analyzed,and it is found that high-speed cutting is beneficial to reduce the defect depth of SiC particles.Finally,the effect of cutting parameters on the surface formation characteristics(surface micro morphology,surface roughness,work hardening and surface residual stress)of SiCp/Al composites is analyzed by controlling variables,and the low defect surface formation process is obtained.The results show that high cutting speed,low radial depth and feed rate can reduce the surface roughness.The higher the cutting speed and the lower the feed rate,the more obvious the surface work hardening degree is.When the cutting speed is in the range of600?2500 m/min,there is residual compressive stress on the machined surface.The residual compressive stress on the surface changes to the residual tensile stress when the feed rate increases to 0.06mm/z.