热处理对Al-0.7Fe-0.2Sc合金慢应变腐蚀拉伸性能影响

采用慢应变腐蚀拉伸测试、扫描电镜、透射电镜观察等手段,研究了在腐蚀环境(腐蚀剂为0.1 mol/L Na2SO4+0.001 mol/L NaCl的混合溶液)下不同热处理工艺对Al-0.7Fe-0.2Sc合金力学性能和微观组织的影响。结果表明,600℃×72 h固溶+325℃×72 h时效为最优工艺,合金伸长率达到13.8%,抗拉强度为131.2 MPa;试样断口形貌由韧窝和撕裂棱组成,韧窝尺寸较小、较浅且数量较多。经过固溶时效,除了已经存在的Al_(3)Fe第二相外,还有大量的Al_(3)Sc析出相,这些相钉扎在位错及亚晶界处,阻碍塑性变形,提高了Al-0.7Fe-0.2Sc合金的力学性能。

Mechanical properties and stress corrosion cracking behaviour of AZ31 magnesium alloy laser weldments

An AZ31 HP magnesium alloy was laser beam welded in autogenous mode with AZ61 filler using Nd-YAG laser system.Microstructural examination revealed that the laser beam weld metals obtained with or without filler material had an average grain size of about 12 μm.The microhardness and the tensile strength of the weldments were similar to those of the parent alloy.However,the stress corrosion cracking （SCC） behaviour of both the weldments assessed by slow strain rate tensile （SSRT） tests in ASTM D1384 solution was found to be slightly inferior to that of the parent alloy.It was observed that the stress corrosion cracks originated in the weld metal and propagated through the weld metal-HAZ regions in the autogenous weldment.On the other hand,in the weldment obtained with AZ61 filler material,the crack initiation and propagation was in the HAZ region.The localized damage of the magnesium hydroxide/oxide film formed on the surface of the specimens due to the exposure to the corrosive environment during the SSRT tests was found to be responsible for the SCC.

钆改性镁合金在溶液中的应力腐蚀行为研究

通过添加质量分数为0.5%,1%,1.5%和2%的Gd对AM50镁合金进行改性,采用金相显微镜、X射线衍射、扫描电子显微镜及腐蚀慢应变速率拉伸研究了目标金属在空气、去离子水和NaCl溶液中的应力腐蚀行为。结果表明,Gd添加后,合金组织中出现了白亮的颗粒状金属间化合物Al_(2)Gd,随着Gd添加量的增加,Al_(2)Gd相的数量和体积增加,而β-Mg_(17)Al_(12)相的数量和体积减少。慢拉伸实验结果显示,在纯水中,随着合金中Gd的含量增加,合金的抗应力腐蚀能力增加;而在NaCl溶液中,0.5%Gd的添加量显示了最优的应力腐蚀抗力。此外,Gd的添加没有改变合金的断裂机制,依旧为准解理断裂。应力条件下,由于腐蚀导致的蚀坑形核和发展是试样最大断裂强度下降的直接原因。随着Gd的含量在合金中增加,膜破裂机制在试样断裂过程中导致的试样形貌变化是试样失效的主要原因。