疲劳循环对A7005铝合金型材组织与力学性能的影响

Effect of Fatigue Cycles on Microstructure and Mechanical Properties of A7005 Aluminum Alloy

采用扫描电镜、透射电镜、X射线衍射和室温拉伸等方法研究了A7005铝合金经不同疲劳循环加载次数对其组织和力学性能的影响。结果表明:A7005铝合金经0、104、105次疲劳循环后,位错密度从初始0.75×10^(14)m^(-2)上升至0.79×10^(14)m^(-2),抗拉强度和屈服强度逐步上升,并在10~5次循环时分别达到最大值402.72、341.92 MPa。经106、107次疲劳循环后,晶粒中开始出现位错胞,大量位错缠结在晶界附近,位错密度急剧上升至1.53×10^(14)m^(-2),晶内时效析出η'亚稳相会吸收溶解的Zn、Mg元素而长大粗化,以及因位错快速增殖而被溶解至基体中,η'亚稳相数量明显减少,降低了时效强化效果。疲劳区域边界上出现很多由第二相粒子脱落所引起的疲劳缺陷,材料的抗拉强度和屈服强度分别下降至396.57、328.07 MPa。

The effects of loading numbers of fatigue cycles on the microstructure and mechanical properties of A7005 aluminum alloy were investigated by SEM, TEM, XRD and room temperature tensile. The results show that the dislocation densities increase from original 0.75×10^14 m-2 to 0.79×10^14 m^-2 after 0, 104 and 105 fatigue cycles. The tensile strength and yield strength of the alloy increase to the maximum 402.72 MPa and 341.92 MPa after 105 fatigue cycles. The dislocation cells appear after 106 and 107 fatigue cycles, then a large number of dislocations are entangled in the vicinity of the grain boundary, and the dislocation density rapidly rises to 1.53×10^14 m2. A part of intracrystalline aging precipitation -q＇ metastable phase grow up and become coarsening because of absorbing the dissolution of Zn and Mg elements, and the others are dissolved into the matrix because of dislocation rapid proliferation. The ageing strengthening effect reduces because the quantity of η＇ metastable phase decreases significantly. The boundary of fatigue zone generates a large amount of fatigue defects due to falling off of the second phase particles. The tensile strength and yield strength of the alloy reduce to 396.57 MPa and 328.07 MPa, respectively.