5A06鋁合金及其焊接接頭的疲勞斷裂行為Fatigue fracture behavior of 5A06 aluminum alloy and its welded joint

對5A06防銹鋁合金及其焊接接頭疲勞性能斷裂行為進行研究，采用疲勞試驗、光學顯微鏡、掃描電子顯微鏡等手段對 5A06 鋁合金的疲勞性能、金相組織、裂紋擴展特征和疲勞斷口進行分析。結果表明：在循環次數為2×10 6 時，鋁合金母材、對接接頭、橫向十字、側面連接和縱向十字接頭的疲勞性能分別為99.97、70.96、57.48、48.20 和 41.80 MPa；鋁合金母材疲勞裂紋起裂于截面最小部位，對接接頭和橫向十字接頭裂紋起裂于焊趾等應力集中部位，裂紋沿著熱影響區擴展；側面連接接頭裂紋起裂于兩板連接處應力集中部位，縱向十字接頭裂紋起裂于熱影響區；微 觀裂紋為沿晶和穿晶混合的擴展特征。對 母材及其焊接接頭的宏觀斷口呈暗灰色纖維狀，具有一定的塑性；接頭的微觀斷口具有準解理特征，斷口中存在球狀孔洞、疲勞條紋和韌窩，并存在二次裂紋。

Fatigue testing fracture behavior was researched on 5A06 antirust aluminum alloy and its welded joints. The
fatigue properties, microstructure, fatigue crack propagation character and fatigue fracture were investigated by fatigue test, optical microscopy (OM) and scanning electronic microscopy (SEM). Under cycle times of 2×10 6, the fatigue strengths of base metal (BM), butt joint (BJ), transverse cross joint (TJ), lateral connection joint (LJ) and longitudinal cross joint(LCJ) are 99.97, 70.96, 57.48, 48.20 and 41.80 MPa, respectively. The fatigue crack initiation site is in the smallest section for base metal, the crack initiation is in the weld toe and the crack propagates along the HAZ for the BJ and TJ, the crack initiation is in the fillet weld leg for the LJ, the crack initiation is in HAZ for the LCJ, the microcrack propagates for transgranular and intergranular. The fatigue macrofracture shows a dark gray fibrous fracture patterns and has some plasticity, the microfracture surface consists of quasicleavage patterns, spherical hole, fatigue striation and dimple, and numerous secondary cracks are observed.

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