High cycle fatigue behavior of bulk 6061Al prepared by cold spray-friction stir processing composite additive manufacturing

In this work, the high cycle fatigue behavior of bulk 6061Al prepared by cold spray-friction stir processing composite additive manufacturing (CFAM) was studied for the first time. The microstructure and fatigue fracture morphology of CFAM sample were characterized by scanning electron microscopy equipped with electron backscattering diffraction. The stress versus number of cycles of failure (S-N) curve for CFAM sample was established, and the fatigue crack growth behavior of CFAM sample was analyzed. The results showed that the microstructure of CFAM sample was denser and more homogeneous compared with cold spray (CS) sample, and the average grain size was refined to 3.3 μm due to dynamic recrystallisation. The dense, homogeneous and fine microstructure delayed the initiation and growth of fatigue cracks, and thus resulted in a 178% increase in fatigue strength in the CFAM sample over CS sample. The fatigue surface of the CFAM sample could be divided into fatigue source zone, crack growth zone, and transient fracture zone, showing typical fatigue fracture characteristics. The fatigue crack growth rate in the CFAM sample was significantly lower than that of CS sample for the same stress intensity factor range (ΔK). This was because the fine grains uniformly distributed in CFAM sample increased the proportion of grain boundaries and hindered the fatigue cracks growth. Therefore, CFAM is a promising technology for preparing bulk 6061 Al with excellent fatigue properties.