材料期刊网

采用SEM, TEM, 动电位极化和浸泡实验研究了机械冷加工变形对汽车散热器高Mn(0.22%, 质量分数, 下同)和低Mn(0.08%)铝合金管在0.6 mol/L NaCl (pH=6)和SWAAT (ASTM G85, pH=3) 溶液中的腐蚀行为的影响. 电化学极化测试表明, 无形变时高Mn铝合金直管的点蚀电位最高; 但冷加工能降低高Mn铝合金弯曲表面的点蚀电位, 而对低Mn铝合金的点蚀电位没有明显影响. TEM观察发现, 冷加工后高Mn铝合金中有大量纳米尺度的富Mn析出相, 在低Mn铝合金中却没有观察到这种析出相. 阴极极化测试表明, 富Mn相能显著促进阴极反应, 富Mn相相对Al基体为阴极相, 因而是点蚀萌生的部位. 添加Mn尽管有利于提高铝合金的耐蚀性, 但机械冷加工会弱化这一效应.

Aluminium alloys are extensively employed as heat transfer tube materials in heat exchangers. Previous work has focused on the corrosion behaviour of tube materials in brazed heat exchangers. However, very little attention has been devoted to corrosion of tubes in mechanically–expanded heat exchangers despite the observation of some instances of early corrosion failure in bent region of aluminium alloy tube. The effects of cold deformation on the corrosion behaviour of aluminium tube materials have been studied in 0.6 mol/L NaCl and SWAAT solutions by SEM, TEM, potentiodynamic polarizations and immersion test. The results show that high Mn content (0.22%, mass fraction) can experience preferential corrosion and early failure in the bent region, but not for one with a lower Mn content (0.08%). SEM/TEM observations of the microstructure of the alloys show that each alloy has one main type of coarse intermetallic particle. However, TEM observations show that there is a distinct difference in particle morphology between the bent and straight regions of the high Mn alloy tube, the ent region has more nano–scale Mn–rich particles than the straight region, and no such effects are observed on the low Mn alloy. The microelectrochemical polarisation measurements show that the straight region of high Mn has highest pitting potential, but cold deformation can decrease the pitting potential of bent region of high Mn tube, but no such effects on low Mn tube. The immersion test shows that the bent region of high Mn alloy has highest attack; this is associated with precipitation of 20—100 nm Mn–rich particles, which cause increased anodic reactivity as they provide further pit initiation sites and cause solute depletion in the matrix. In addition, the Mn–rich particles are aso sites for enhanced cthodic reactivity. The relationship between the microstructure and electrochemicaproperties of tube materials before and after cold deformation is established. The results indicate Mn can improve the corrosion resistance of aluminium alloy, but the mechanical cold deformation will weaken the effect.