Evolution of grain structure in AA2195 A1-Li alloy plate during recrystallization

The evolution of the grain structures in AA2195 Al-Li alloy plate warm-rolled by 80% reduction during recrystallization annealing at 500℃ was investigated by electron backscatter diffraction, scanning electron microscopy and transmission electron microscopy. It is found that the elongated grain structures are caused by the lamellar distribution of recrystaUization nucleation sites, being lack of large second phase particles （〉 1μm）, and dispersive coherent particles （such as δ′ and β′concentrated in planar bands. The recrystallization process may be separated into three stages： firstly, recrystallization nucleation occurs heterogeneously, and the nuclei are concentrated in some planar zones parallel to rolling plane. Secondly, the grain boundaries interacted with small particles concentrate in planar bands, which is able to result in the elongated grain structures. The rate of the grain growth is controlled by the dissolution of these small particles. Thirdly, after most of small particles are dissolved, their hindrance to migration of the grain boundaries fades away, and the unrecrystallized zones are consumed by adjacent recrystallized grains. The migration of high angle grain boundaries along normal direction leads a gradual transformation from the elongated grains to the nearly equiaxed, which is driven by the tension of the grain boundaries.     

时效对7055铝合金淬火敏感效应的影响

通过电导率、常温力学性能测试和透射电镜研究了时效对7055铝合金淬火敏感效应的影响。结果表明:合金固溶后慢速淬火时,晶粒内部和晶界上析出大量粗大的η平衡相,基体中的溶质过饱和度及空位浓度大大降低,不利于时效时强化相的均匀弥散析出,导致合金的力学性能下降;双级时效对快速淬火合金的力学性能影响不大,但提高了慢速淬火合金的力学性能,因而一定程度减少了合金的淬火敏感效应;这是因为相对单级时效而言双级时效可使慢速淬火合金中得到更多强化相,分布也更均匀弥散,从而减小空位浓度降低带来的不利影响;在本研究中,100℃,24 h 121℃,24 h是最佳的双级时效制度。     

Effect of step-quenching on microstructure of aluminum alloy 7055

The effect of step-quenching on the microstructure of aluminum alloy 7055 after artificial aging was studied by hardness testing and transmission electron microscopy (TEM). Step-quenching leads to decomposition of solid solution and heterogeneous precipitation of equilibrium phase mainly on dispersoids and at grain boundaries; thus lower hardness after aging. Prolonging isothermal holding at 415 ℃ results in coarser and more spaced η phase particles at grain boundaries with wider precipitates free zone, and lower density of larger η′ hardening precipitates inside grains after aging. Isothermal holding at 355 ℃ results in heterogeneous precipitation of η phase both on dispersoids and at grain boundaries. Isothermal holding at 235 ℃ results in heterogeneous precipitation of η phase first, and then S phase. Precipitates free zones are created around these coarse η and S phase particles after aging. Prolonging isothermal holding at these two temperatures leads to fewer η′ hardening precipitates inside grains, larger and more spaced η phase particles at grain boundaries and wider grain boundary precipitates free zone after aging.     

分流模挤压焊合区域的氧化物分布及焊合组织分析(英文)

利用有限元分析、扫描电子显微镜及金相实验研究分流模的锭接锭挤压条件下,型材纵、横向焊合区域的氧化物分布及焊缝微观组织。结果表明:氧化物仅存在于型材基体与横向焊合区域结合面;纵向焊缝表现为深色条纹状组织,包含在强剪切变形及高温条件下形成的粗大再结晶晶粒中;横向焊缝组织表现为晶粒度略小的等轴再结晶晶粒。     

7020铝合金型材的疲劳行为及微观机制

采用光学显微镜、扫描电镜、扫描透射电镜和电子背散射衍射等分析方法研究了7020铝合金型材疲劳行为及微观机制。结果表明在应力比R为0、疲劳极限寿命取10~7周次时,合金疲劳强度为232.9 MPa。疲劳裂纹尖端应力强度因子ΔK=8 MPa·m~(1/2)时,裂纹扩展速率约为6.44×10~(-5 )mm/cycle。合金中尺寸在3～12μm的粗大难熔结晶相不仅易成为疲劳裂纹源,也会加速疲劳裂纹扩展。在未再结晶区域,疲劳裂纹主要以穿晶方式扩展。当裂纹扩展到易滑移平面取向差较大的再结晶小晶粒时,裂纹易沿其大角度晶界快速扩展。合金再结晶程度及其对应的大角度晶界占比越低时,疲劳裂纹扩展路径越曲折,扩展速率越慢。     

固溶处理对7A55铝合金局部腐蚀性能的影响

采用电化学测试、浸泡实验、金相显微镜、扫描电镜、透射电镜等实验手段研究固溶处理对7A55铝合金局部腐蚀性能的影响。结果表明:轧板中大量的第二相使轧板发生严重的腐蚀,整个表面被剥落下来。单级固溶的再结晶程度较低,亚晶组织细小,但合金残留第二相较多,耐蚀性能差。低温回复+高温固溶处理(450℃/1h+480℃/30min)可以将粗大第二相大部分溶解,且获得最少的再结晶分数和细小亚晶组织。实验结果表明,450℃/1h+480℃/30min固溶处理具有最佳的耐局部腐蚀性能。     

回归再时效中预时效温度对7050铝合金应力腐蚀性能的影响

采用硬度测试、电导率测试、慢应变速率拉伸、透射电镜和扫描电镜等方法,研究了回归再时效热处理工艺中预时效温度对7050铝合金微观组织和应力腐蚀性能的影响。结果表明:随着预时效温度升高,回归再时效后7050铝合金晶内析出相从以GP区为主转变为以η′相为主,晶界析出相逐渐粗化,晶界变得不连续分布,合金应力腐蚀敏感性降低;但晶界无沉淀析出带宽度增加,120℃时达到140nm,易导致应力集中和阳极溶解,合金抗应力腐蚀性能下降。预时效温度为80℃,即稍微欠时效时,7050铝合金抗应力腐蚀性能较好,在缓慢应变速率(10-6s-1)和3.5%NaCl溶液腐蚀介质下,合金抗拉强度为473.5MPa,伸长率为10.67%,应力腐蚀指数为0.05824。     

我所认识的2A3

三极胆中 最佳选择 300B和2A3．两者的功率及音色都有明显区别，但无论过去或今天它们都是最多人使用的三极管。撇开个人喜好来说．最先生产300B的西电差不多是选择300B的唯一选择．相反2A3除RCA外就有数款不同厂不同款的选择．单以此点来说2A3肯定比300B为佳．如再加上价格因素．就算是2A3中最昂贵、与300B齐名的单屏2A3，市价也只是前者的几分之一．如与一般双屏2A3比较。     

均匀化升温速率对7N01铝合金组织与力学性能的影响

采用光学显微镜、扫描电镜、电子探针显微镜、透射电镜和常温拉伸等测试方法研究均匀化升温速率对7N01铝合金显微组织和力学性能的影响。结果表明:与升温速率较快的均匀化制度相比,采用升温速率小于100℃/h的慢速升温均匀化制度更有利于细小弥散Al3Zr粒子的析出,使Al3Zr粒子分布均匀;细小弥散的Al3Zr粒子能有效地阻止再结晶晶界的迁移,抑制再结晶的发生。随着均匀化升温速率由500℃/h降低到20℃/h,析出的Al3Zr粒子数量增加,尺寸减小,析出相体积分数和半径的比值φ/r由75.8μm-1增大到359.1μm-1,使得Al3Zr粒子对晶界的钉扎力增大,因此合金的再结晶分数相应地由31.92%逐渐降低到1.32%;保留下来的大量位错和未再结晶组织提高了合金的综合力学性能。     

7A55铝合金热变形的速率控制机制(英文)

利用Gleeble-3500热模拟试验机对7A55铝合金在300~450°C温度范围和0.01~1 s-1应变速率范围内的热变形行为进行研究。建立了7A55铝合金的热加工图,对该合金的热变形行为进行了遵循幂律关系的动力学速率分析。结果表明:7A55铝合金在410~450°C和0.05~1 s-1的热变形条件下发生了动态再结晶。热加工图的分析结果与动力学分析结果的吻合度较高。动态再结晶及动态回复变形的表观激活能分别为91.2和128.8 kJ/mol,这说明7A55合金的动态再结晶机制为晶界自扩散,而动态回复机制为位错的交滑移。