Research On Fatigue Behavior Of Spray Deposited SiC_p/Al-20Si Composite And Matrix Alloy

15%（Vol%）4.5μm SiC_p/Al-20Si composite and matrix alloy were prepared byspray deposition. The mechanical properities under ambient temperature, high cyclefatigue and fatigue crack growth behaviour were investigated. The results are asfollows:The addition of SiC particles increases the mechanical properities by improvingthe microstructure of the composite, refining the grain size and inhibiting graingrowth.It is found in the high cycle fatigue research that the fatigue life of SiC_p/Al-20Sicomposite as well as the matrix material increases as the stress amplitude decreases.The former fatigue life is far higher than the latter one at the same stress amplitudelevel. The fatigue crack nucleates from the fractured large granular primary crystalsilicons or the peled area of Si phase. The particle size of SiC in the composite is sosmall that cannot easily fracture. Henth, when the crack encounters the SiC particleduring the nuclearation, it will steer by or be impeded. Therefore, the crack can onlypropagate in the matrix alloy, which increases the nucleation area, and thus improvethe fatigue life. The pele and fracture of the Si particles, as well as the pele of the SiCparticles from the matrix are the main machanism in the fatigue failure of thecomposite.The threshold value of SiC_p/Al-20Si and Al-20Si alloy are4.13and3.95MPa m^1/2respectively. The resistance of the composite exceeds the alloy consistentlyat the same ΔK levels until fractured. When the crack encounters Si and SiC particles,strong interactions will happen. At lower ΔK value（near the threshold value）, thedeflection and inflection of the fatigue crack,which roughen the crack surface andhenth induce crack closure and increase the fatigue crack growth resistance, caused bycircumventing Si particle is the dominated crack propagation machanism. However, asΔK increases, the trend of crack propagating along the interface of Si particle and Almatrix increases, simultaneously accompanied by the frequently fracture of Si particle.The deflection of the crack circumventing SiC particle and the microcracks generatingin the SiC particle both increase the energy consuming in crack propagation, whichincrease the fatigue crack growth resistance. Particularly, the extent of the crack closure effect in composite is greater than that in matrix because of the microcracksgenerating in the SiC particle.