Effects of cooling velocity on multiaxial fatigue behavior of A319 alloy under circular loading conditions
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摘要: 采用MTS809型電液伺服疲勞試驗機、掃描電鏡研究了不同冷卻速度對A319鋁合金圓形加載路徑下的疲勞特性.結果表明:當冷速為10℃·s-1時,材料中二次枝晶臂間距、硅顆粒及孔洞尺寸較冷速為0.1℃·s-1時要小.二次枝晶臂間距較小時,滯后回線面積小,材料應力應變近乎同相,且附加強化效果明顯.不同冷速條件下裂紋萌生位置不同,在冷速為10℃·s-1的材料中,裂紋在大硅顆粒處萌生,隨著冷速降低至0.1℃·s-1時,裂紋位于孔洞處萌生.對于A319鑄造鋁合金來說,冷速的變化對其軸向與切向循環特性并無直接影響,軸向表現為先硬化再軟化,切向表現為先硬化后穩定的趨勢.Abstract: The effects of cooling velocity on the multiaxial fatigue properties of A319 alloy under circular loading conditions was studied by using the MTS809 servo-hydraulic testing system and scanning electron microscopy. The results indicate that the solidification cooling velocity of 10℃·s-1 leads to decrease in the size of microstructures, such as second dendrite arming space, Si particle, and void compared. Hysteresis loops with smaller second dendrite arming space show that there is almost no phase angle between strain and stress along the axial direction. Furthermore, the decrease in second dendrite arming space size manifests as a more remarkable additional hardening effect compared to that of the sample with a cooling velocity of 0.1℃·s-1. The local regions of crack initiation are completely different. The cracks in samples solidified at a cooling velocity of 10℃·s-1 initiate and propagate from large Si particulars, in contrast to the cracks in samples solidified at a cooling velocity of 0.1℃·s-1, which initiate from pores. It is also found the A319 samples under the two different cooling velocities show initial cyclic hardening followed by cyclic softening in the axial direction and initial cyclic hardening followed by stable tendency in the shear direction.
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Key words:
- A319 aluminum alloy /
- cooling velocity /
- circular loading /
- second dendrite arming space
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參考文獻
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