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 p ropagation of small fatigue cracks. Small cracks nucleated from defect s on both as-cast and polished surfaces. However, the large (approxima tely 90 mum in diameter) surface defects found on as-cast surfaces cau sed an approximate 20% reduction in fatigue life when compared to poli shed surfaces where cracks initiated from smaller (approximately 12 mu m in diameter) microporosity. Integration of averaged small fatigue cr ack growth data enables the fatigue lives of both types of specimen to be predicted at stresses above the fatigue limit, showing that the di fference in fatigue behaviour is principally due to the extra period o f crack growth in the polished surfaces.