Impact of cooling rate on exfoliation corrosion resistance of a Li-containing 7xxx aluminum alloy

The impact of cooling rate after solution heat treatment on exfoliation corrosion resistance of a Li-containing 7xxx aluminum alloy was investigated by accelerated immersion and electrochemical impedance spectroscopy test,optical microscope,electron backscatter diffraction and scanning transmission electron microscope.With the decrease of cooling rate from 1700℃/s to 4℃/s,exfoliation corrosion resistance of the aged specimens decreases with rating changing from EA to EC and the maximum corrosion depth increasing from about 169.4μm to 632.1μm.Exfoliation corrosion tends to develop along grain boundaries in the specimens with cooling rates higher than about 31℃/s and along both grain boundaries and sub-grain boundaries in the specimens with lower cooling rates.The reason has been discussed based on the changes of the microstructure and microchemistry at grain boundaries and sub-grain boundaries due to slow cooling.

焊后时效对7046铝合金搅拌摩擦焊接头力学性能的影响

对厚度为3.5 mm的7046铝合金挤压板材进行搅拌摩擦焊接并对焊接接头进行人工时效,研究了焊后时效对接头力学性能的影响。结果表明,焊接接头时效前的硬度分布大致呈"W"形,抗拉强度为406.5 MPa,焊接系数为0.8,拉伸时在后退侧热影响区与热机影响区的过渡位置出现断裂,此处的硬度值最低,断裂面上有大量的韧窝;进行120℃×24 h时效后,接头的热影响区、热机影响区和焊核区的硬度都显著提高,母材区的硬度变化不大,硬度分布大致呈"一"形,抗拉强度大幅度提高到490 MPa,焊接系数达到0.96,拉伸时在焊核区中心断裂,断裂面有大量的沿晶裂纹。时效后接头区域的晶内GPI区转变成具有更好强化效果的η′亚稳相,使接头的硬度和强度提高;与其它区域相比,焊核区中晶界η相的分布更连续,晶界处无沉淀析出带的体积分数更大,因此容易成为拉伸时的断裂位置。

WC预制体柱增强铁基复合材料的显微组织和性能

采用砂型铸造工艺制备具有预制体结构的WC颗粒增强铁基复合材料,研究不同预制体直径对WC增强铁基复合材料的显微组织和三体磨料磨损性能的影响。结果表明,预制体直径为5mm和10mm时,预制体与基体间均产生了明显的过渡层。复合材料的显微组织主要有含WC、Fe_(3)W_(3)C和M_(7)C_(3)型碳化物,且过渡层和预制体区域比高铬铸铁基体具有更高的硬度,预制体直径为10mm的复合材料具有最小的磨损失重,耐磨性最佳,磨损形貌主要表现为犁沟和剥落等特征。

人工时效对7003/7046铝合金搅拌摩擦焊接头组织和力学性能的影响

采用差示扫描量热分析、硬度、室温拉伸实验、背散射电子衍射和透射电子显微镜等手段研究了焊后人工时效对7003-7046异种铝合金搅拌摩擦焊接(FSW)接头的微观组织和力学性能的影响。结果表明:FSW接头后退侧(7046铝合金侧)的硬度明显高于前进侧(7003铝合金侧),两侧平均硬度的差约为30HV;人工时效后接头的硬度提高,两侧平均硬度的差增大到约50HV,接头的屈服强度提高,抗拉强度略有提高,伸长率几乎不变。根据时效前后FSW接头不同区域微观组织的特征,分析了接头力学性能变化的原因。