【作者】 张建波；

【导师】 张永安；

【作者基本信息】 北京有色金属研究总院 ， 材料科学与工程， 2011， 博士

【摘要】 新型Al-Cu-Mg-Ag系合金由于具有优良的高温及损伤容限性能成为下一代超音速飞行器蒙皮的候选材料。本文在选择Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr合金合理的单级固溶工艺的基础上,研究了单级时效对合金性能的影响,通过定性和半定量的分析方法研究了单级时效过程中沉淀相的析出行为,并进一步研究了多级断续时效对合金组织和性能的影响,最后评价了单级时效态合金的疲劳性能和高速冲击性能。主要工作及结果包括：研究了固溶温度和时间对Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr合金组织性能的影响。合金的合理的单级固溶温度为520℃-525℃之间,合理的单级固溶时间为2h左右。研究了单级时效温度和时间对Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr合金电导率、硬度和室温拉伸性能的影响。在自然时效时,合金的电导率先减小后趋于稳定,合金的硬度先增大后趋于稳定；在确定的人工时效温度下,随着时效时间的延长,合金的电导率先增大后趋于稳定,合金的硬度先增大后减小。时效温度为160℃左右时,合金的峰值硬度最高,约为HV=166。重点研究了160℃和180℃单级时效对Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr合金拉伸性能的影响。在两个温度下时效时,合金峰值力学性能无明显差异,峰值抗拉强度为510MPa左右,峰值屈服强度为475MPa左右,对应的延伸率在14%左右；两个温度下的时效强化响应速度具有明显的差异,温度越高,强度增加越快,在较高的时效温度下,峰时效后强度的下降速度加快。定性研究了单级时效下Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr合金沉淀相的析出行为。在较低温度(65℃)时效时,合金的主要沉淀相为θ’相,无明显的Ω相析出特征；在中等温度(160-180℃)时效时,合金的沉淀相为Ω相和少量的θ’相；在较高温度(>200℃)时效时,合金的沉淀相与中等温度时效相同,但长大速度明显加快。重点研究了中等温度时效对合金组织的影响,在时效初期,沉淀相尺寸均匀细小,不发生交义；随着时效时间的延长,沉淀相的尺寸出现不均匀特征,且发生明显的交接和交义现象,在交接、交义区与基体的界面附近出现位错,说明沉淀相的交接和交义需要位错协调。研究分析了固溶淬火态Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr合金在差示扫描量热试验中的三个放热效应所对应的析出反应。三个放热峰的峰值温度分别约为Ⅰ：171℃,Ⅱ：230℃和Ⅲ：276℃,Ⅰ峰对应的反应是GP区的结构调整,Ⅱ峰对应的是Ω相的析出,Ⅲ峰对应的主要是θ’相的析出。利用HREM半定量分析了中等温度时效Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr合金Ω相的析出行为。时效温度越高,Ω相的厚度和径向尺寸越大,峰值面积分数基本一致,但达到峰值面积分数的时间不同,温度越高,时间越短。利用小角度X散射研究了合金单级时效过程中沉淀相的析出行为。在160-200℃范围内,随着时效时间的延长,散射花样由同心圆过渡到枝权状花样,且时效温度越高,出现枝权的时间越短；枝权花样是盘状沉淀相在倒易空间中傅里叶变换引起的,通过测量枝权间的角度可以识别枝权在正空间中对应的沉淀相种类；此外,文章计算了沉淀相的回转半径和积分强度。研究了多级断续时效制度对Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr合金组织和性能的影响。断续时效在保持单级时效强度的条件下,可提高合金的断裂韧性。微观组织分析表明,断续时效与中等温度单级时效对组织影响的差异主要在于第二级低温时效时,合金的沉淀相为均质形核的θ’相,无明显的Ω相析出特征。研究了时效制度对Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr合金疲劳和高速冲击性能的影响。峰时效态合金具有良好的抗疲劳性能,疲劳极限为291MPa,且欠、峰、过时效态合金均具有较低的疲劳裂纹扩展速率,其中峰时效态合金的最低；霍普金森试验表明,160℃/2h、14h和50h处理后合金具有不同的应变强化效应,其中50h处理后的合金在低速和高速冲击下屈服强度差异最大,2h和14h时效后合金在高速和低速冲击下的屈服强度差异较小。更多还原

【Abstract】 A novel series of Al-Cu-Mg-Ag alloy with excellent elevated temperature properties and damage-tolerance was developed and became a candidate skin alloy for next generation of supersonic aircraft. The variation of microstructure and properties of a novel Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr alloy in solution and single ageing process was studied in this thesis. Furthermore, the effect of Muti-step ageing on properties and microstructure was also investigated. The fatigue and dynamic properties were estimated at the last part of this thesis. The main results were drawn as below:The effect of solution temperature and time on microstructure and properties on Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr alloy was studied. The rational single solution temperature is in the range of 520℃-525℃. The rational single solution time is about 2 hours.The influence of single ageing temperature and time on electrical conductivity, hardness and ambient tensile properties was investigated. Under the condition of natural ageing, the electrical conductivity of alloy decreases initially and then approaches to a stable value, while the hardness increases initially and then trends to a stable value. Under the condition of artificial ageing, the electrical conductivity of alloy increases initially and then trendes to a stable value, while hardness increases initially and then decreases after having reached the top value. When the ageing temperature reaches 160℃,the top value of hardness is the highest among all the ageing temperatures, i.e.HV=166.The focal discussion was put on the effect of ageing at 160℃and 180℃on the tensile properties of Al-4.8Cu-0.5Mg-0.3 Ag-0.15Zr alloy. When ageing at these two temperatures, the peak values of tensile property are not significantly different from each other. The peak value of UTS is about 510MPa, while YTS is about 475MPa, and the corresponding value of Elongation is about 14%. However, the responding of ageing-hardening is different. The higher ageing temperature, the faster increment of strength is obtained. The speed of reduction of strength after peak ageing increased with the increment of ageing temperature.The ageing behavior of Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr alloy in the process of single ageing was studied qualitatively. At low ageing temperature (65℃), the precipitate is mainly 0’phase without visible characteristic ofΩphase. At moderate ageing temperature (160-180℃), the precipitates areΩphase and small quantitative ofθ’ phase. At elevated ageing temperature (>200℃), the type of precipitates is the same with that of the ageing at moderate temperature, but the speed of growth increases. The effect of moderate temperature on microstructure of the experimental alloy was studied emphatically. At the early ageing period, the size of precipitates is uniform and the precipitates are not crossed with each other. As increment of ageing time, the size of precipitates becomes heterogeneous. Apparent joining of precipitates and crossing zone starts to happen. Beside the field between the joining or crossing zone and the matrix, apparent dislocations are visible, which suggests the joining or crossing of precipitates requires dislocations to coordinate the different structure.The precipitation reactions corresponding to three exothermic effects in DSC experiment of Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr was studied. The peak temperatures of the three effects areⅠ=171℃,Ⅱ=230℃andⅢ=276℃.The corresponding reactions are arrangement of GP zone structure, the precipitation ofΩphase and the precipitation of 0’ phase.The ageing behavior of Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr alloy at moderate temperature was semi-quantitatively investigated. The higher the temperature is, the greater the size of thickness and diameter ofΩphase is obtained. The peak value of fractions ofΩphase at 160℃and 180℃are nearly equal to each other, but the time corresponding to the peak values are different. The higher the temperature is, the shorter the time is required.Small angle X-Ray scattering was used to study the ageing behavior of the experimental alloy. Within the ageing temperature range of 160-200℃,as increase of the ageing time, the scattering patterns changed from concentric cycles to branches. The higher the ageing temperature is, the shorter the time for branches to appear is obtained. The branches are the result of Fourier transformation of plate-like precipitates. The corresponding precipitate of a branch can be identified by the angles between branches. Furthermore, the Guinier radius and integrated intensity were measured using SAXS. The tendency of the SAXS results is different significantly from that of HREM.The influence of typical Muti-step ageing processes on the microstructure and properties was studied. Muti-step ageing can rise the fracture toughness while keeping the strength and elongation of single ageing. The results indicate that the difference between Muti-step ageing and single ageing arises from 0’being separated out homogenously without any visible characteristic ofΩphase during the second low temperature ageing of Muti-step ageing,.The effect of ageing condition on fatigue and dynamic properties of Al-4.8Cu-0.5Mg-0.3Ag-0.15Zr was investigated. The alloy that undergoes ageing at peak conditions has an excellent fatigure property. The fatigue limit is about 291 MPa. The crack propagation resistant of the alloy under different ageing conditions is low. In addition, the results of Hopkinson showes that the strain hardening behavior are different when the alloy is aged at the condition of 160℃/2h,160℃/14h and 160℃/50h. Under low and high attacking speeds, YTS of the alloy aged at 160℃for 50h significantly varies while that of the alloy aged at 160℃for 2h and 160℃for 14h are indistinctively.更多还原