B₄C/BN-Al Surface Composites Prepared By Friction Stir Processing

Aluminum and aluminum alloy products are widely used in aerospace,navigation,aviation,automobile,construction and other fields because of their low density,high specific strength and good corrosion resistance.However,due to the poor wear resistance of aluminum alloy,its industrial application is limited.Particle reinforced aluminum matrix surface composites prepared by friction stir processing can improve the wear resistance of aluminum alloy surface while maintaining the original excellent mechanical properties of aluminum alloy.However,when preparing this material by friction stir processing,the problem of uneven particle distribution is often encountered.The uniformity of distribution of particles can be improved by adopting particle reinforcement with lamellar particles mixed with hard particles.Therefore,B4C/BN hybrid particles reinforced aluminum matrix surface composites were prepared by friction stir processing.Through the combination of simulation and experiment,the particle distribution law was studied,and the preparation process of hybrid particle reinforced aluminum matrix surface composites was found by orthogonal test of single particle reinforced aluminum matrix surface composites.The mass ratio of BN to total particles was 0%,10%,30%,50%and 100%.The specific research contents are as follows:（1）The thermal-mechanical coupling dynamic model of friction stir single-pass processing was established on ABAQUS for simulation.The simulation results showed that the temperature field distribution of the composite layer was asymmetric,and the temperature on the advancing side was higher than that on the returning side;By setting tracer particles,the running track and distribution of particles were simulated.The distribution range of particles on the advancing side was wider,and it was easier to distribute in the area within 2mm from the surface of composite layer.（2）B4C-Al surface composites were prepared by 1～4 passes of processing.It was found that multi-pass processing improved the pore defects caused by particle agglomeration,and changed the processing direction between different passes to make the particle distribution more uniform.After four passes of processing,the defects disappeared and the particle distribution were uniform.（3）In this paper,B4C-Al surface composites with different process parameters were prepared by designing orthogonal tests.It was found that there were interactions among the factors in variance analysis.Therefore,the process parameters for preparing hybrid particle reinforced aluminum matrix surface composites were selected from nine groups of orthogonal tests:rotation speed 700rpm processing speed 60mm/min,and reduction amount 0.2 mm.（4）It was found that the smallest grain size was 2.95μm when only BN was added,because BN provided nucleation point for dynamic recrystallization behavior.With the increase of BN content,the iron-rich phase in the stirring zone became finer.（5）The hardness,wear resistance and corrosion resistance of particle reinforced aluminum matrix surface composites were analyzed.The composites with only B4C particles had the highest hardness and the best corrosion resistance.When the mass ratio of BN was 50%,the corrosion resistance of particle reinforced aluminum matrix surface composites was stronger than that of parent metal.