Influence of Surface Conditions on the Fatigue Behavior of A357 Aluminum Alloy

Abstract

The influence of surface conditions on the fatigue behavior A357 aluminum alloy was studied in this paper. Four-point bending fatigue tests method were performed to obtain the fatigue strength of A357 cast aluminum alloy specimens with different surface conditions. A joint bearing rig was designed to minimize the experimental error caused by the misalignment associated with a four-point bend test. The results showed that the fatigue strength of specimens with as-cast surfaces was higher those with machined surface roughness of Ra=1.6μm and 3.2μm, while lower than that with Ra=0.4μm. Optical microscope (OM) and scanning electron microscope (SEM) observations, indicating that the fatigue cracks initiate from machined grooves for specimens with roughness of Ra=1.6μm and 3.2μm, while subsurface crack initiates from cast defects inside the specimen with roughness of Ra=0.4. For specimens with as-cast surface, the fatigue cracks initiate from the surface irregularities or cast defects near the surface.