Fatigue Properties of Al-12Si-CuNiMg Cast Aluminum Silicon Alloy under Multi-axial Loading

The Al-12Si-CuNiMg cast aluminum silicon alloy was subjected to proportional and 90° nonproportional multi-axial loading fatigue test under 160, 150, 140 MPa equivalent stress amplitudes. The fatigue life of the specimen was tested. The prediction accuracy of fatigue lives under two loading modes by the maximum principal stress model and the critical surface damage parameter Matake model was compared. The fatigue fracture was analyzed. The results show that under the same equivalent stress amplitude, the fatigue life of the non-proportional loaded specimen was much lower than that of the proportional loaded specimen. The fatigue lives estimated by the maximum principal stress model and the Matake model both had high accuracy under proportional loading. Under nonproportional loading, the fatigue lives estimated by the maximum principal stress model had larger errors while those by the Matake model still had high accuracy. The Matake model model was suitable for multi-axial loading fatigue life estimation of this material. The alloy under nonproportional multi-axial loading showed brittle fracture. The crack source was at the oxide inclusions near the surface, and the crack propagation region showed quasi-cleavage transgranular fracture, accompaning with secondary cracks.