The High-cycle Fatigue Behavior And Damage Mechanism Analysis Of B₄C/6061Al Composite

The Al matrix composites are the excellent candidates for many structure application,especially the aerospace and automotive industries,due to its lightweight,superior modulus and enhanced mechanical properties such as wear resistance and high-cycle fatigue behavior.Especially for the ceramic particle reinforced metal matrix composites?PMMC?,which possesses the better isotropic properties compared to the fibre reinforced composites,are gaining more attention.The low cost of fabrication also make PMMC easier to be applied.In order to obtain both the mechanical and neutron absorb properties of the composites,the B₄ C particle was used as the reinforce phase.The B₄ C particle is of great strength and thermal stability and can form a better interfacial bonding with aluminum matrix than that SiC and Al2O3 particle.Moreover,on account of the high neutron absorption cross-section of 10 B,the B₄ C can also provide the composites neutron shielding capability.The strength of PMMC is closely related to the volume fraction of the reinforcement,theoretically speaking,the strength of composites is proportional to the volume fraction of the reinforce phase,but with the fraction increase the composites will suffer severe metallurgical defects,and the machinability of composites will dramatically reduce.In this study,the 30 wt.% B₄ C reinforced 6061 Al matrix composite plate was preparation through powder metallurgy,and successfully processed the composite billet into 3mm thick plate.The tensile and fatigue properties were tested and the failure mechanical were analyzed.The tensile property of the composite is slightly weakened compared to the commercial 6061 Al,but with a sharp increased elastic modulus of 110 GPa.The fatigue test of B₄C/6061 Al indicates that the fatigue resistance of the composites is more favorable than the 6061 Al.The fatigue limit of B₄C/6061 Al is 165.7MPa,presented a clear increase compared to the Al matrix.However,when the fatigue stress increases and reaches the yield strength of the composites,the B₄C/6061 Al shows a degradation of fatigue resistance.This degradation of fatigue property is more severe than the alloy with lower yield strength.The fatigue strain during the fatigue test was monitored to analysis the failure mechanism under cyclic loading.To gain insight of the B₄C/6061 Al damage mechanism under fatigue stress,the stress-strain behavior of the composite was studied.The evolution of microstructure was also studied through the real-time acoustic emission?AE?signals.According to the plastic accumulate rate,fatigue life of the composite could be divided into three stages,and the secondary stage of the fatigue process is a relative stable stage due to the cyclic hardening.To characterize the full fatigue process of B₄C/6061 Al composite,the AE signals were monitored during the test,and the AE-strain coupled analysis system was founded and employed to describing the micro scale evolution of the composite during the fatigue test.According to the AE signal,before the crack initiating,the low-amplitude AE signal will increase sharply due to intense interfacial debonding.At the same time the relationship between the AE amplitude and dynamic elastic modulus was founded during the fatigue process,the relationship indicates that the AE amplitude grew in inverse proportion to the dynamic elastic modulus during the fatigue process.Combined with the stiffness degradation rule the AE signal presented an explanation to the fatigue damage mechanism evolution of the 30 wt.% B₄C/6061 Al.