Al-Mg-Si-Cu合金時效狀態(tài)對疲勞過程及斷裂特征的影響Effect of precipitation state on fatigue process and fracture characteristics of Al-Mg-Si-Cu alloy

采用疲勞測試、拉伸試驗、金相顯微電鏡、掃描電鏡和透射電鏡技術研究不同時效處理狀態(tài)的Al-Mg-? Si-Cu合金在循環(huán)載荷作用過程中力學性能的演變和疲勞斷口特征。結果表明：過時效合金的疲勞壽命最長，峰值時效合金的疲勞壽命最短；欠時效和峰值時效合金的屈服強度在疲勞過程中出現(xiàn)下降，且欠時效合金表現(xiàn)得尤為顯著，欠時效合金的伸長率隨循環(huán)次數(shù)的增加而增加；過時效合金的強度在疲勞過程中得到提高，而伸長率在疲勞壽命后期出現(xiàn)大幅下降。疲勞裂紋在樣品表面萌生后傾向于沿晶界增殖并形成裂紋源區(qū)，過時效合金在射線狀裂紋增殖區(qū)與瞬斷區(qū)之間還出現(xiàn)了沿晶擴展區(qū)。

Under cyclic loading the evolution rules of mechanical properties and the fractographs of the Al-Mg-Si-Cu alloy samples aged for different times were investigated by the fatigue test, tensile test, optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the fatigue life of the over-aged alloy is the longest, while that of the peak-aged alloy is the shortest. The yield strengths of the under-aged and peak-aged alloys decrease during the fatigue process, especially for the under-aged alloy, while the elongation of the under-aged alloy increases steadily with the increase of fatigue cycles. For the over-aged alloy, the strength increases during the fatigue process, whereas the elongation drops sharply in the late fatigue stage. The fatigue fracture analysis reveals that the cracks are inclined to grow along the grain boundary after initiating on the specimen’s surface and the crack-source-regions form. Interestingly, grain boundary separation regions were observed between the ray-like crack growth region and the over-loading region in the over-aged alloy.

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