Study of Bending Fatigue Properties of Al-Si Cast Alloy

Fatigue properties of casting Al-alloys are very sensitive to the microstructural features of the alloy (e.g. size and morphology of the eutectic Si, secondary dendrite arm spacing – SDAS, intermetallics, grain size) and casting defects (porosity and oxides). Experimental study of bending fatigue properties of secondary cast alloys have shown that: fatigue tests up to 10⁶-10⁷cycles show mean fatigue limits of approx. 30-49 MPa (AlSi9Cu3 alloy – as cast state), approx. 65-76 MPa (AlSi9Cu3 alloy after solution treatment) and 60-70 MPa (self-hardened AlZn10Si8Mg alloy) in the tested casting condition; whenever large pore is present at or near the specimen’s surface, it will be the dominant cause of fatigue crack initiation; in the absence of large casting defects, the influence of microstructural features (Si morphology; Fe-rich phases) on the fatigue performance becomes more pronounced.