EFFECT OF SURFACE TEXTURE ON FATIGUE LIFE IN A SQUEEZE-CAST 6082 ALUMINUM-ALLOY

The effect of surface texture on fatigue life in a squeeze-cast Al-Mg-Si alloy has been investigated in terms of initiation and subsequent propagation of small fatigue cracks. Small cracks nucleated from defects on both as-cast and polished surfaces. However, the large (approximately 90 mum in diameter) surface defects found on as-cast surfaces caused an approximate 20% reduction in fatigue life when compared to polished surfaces where cracks initiated from smaller (approximately 12 mum in diameter) microporosity. Integration of averaged small fatigue crack growth data enables the fatigue lives of both types of specimen to be predicted at stresses above the fatigue limit, showing that the difference in fatigue behaviour is principally due to the extra period of crack growth in the polished surfaces.