1、General Metal Finishing Contact (galvanic) corrosion 关于接触腐蚀 G. Krolik Guangzhou China 2015/12/11 Proprietary and Confidential General Metal Finishing What is contact corrosion? 什么 是接触腐蚀 ? Proprietary and Confidential Different metals show different chemical behavior 不同金属 有不同的化学特性 Related to environm
2、ental conditions与周围环境有关系 Type of electrolyte which surround the metal金属周围的电解液 Ion content离子的含量 pH Oxigen content 氧气含量 Temperature 温度 etc. 其它 . To compare the metals the electrochemical potential can be measured under different conditions 在不同条件下 ,金属间的电位差可以通过测量并比较 If the difference in the potential is
3、 100 mV contact corrosion is probable 当不同金属间的电位差 100 mV时 很有可能发生接触腐蚀 Contact corrosion What is contact Corrosion? G. Krolik - Guangzhou China - 2015/12/11 3 Proprietary and Confidential If two or more electrical conencted different metals are dipped in an electrolyte, electrons will flow from the les
4、s noble metall to the nobel metal. 当两种或两种以上通电的金属浸泡在电解液中 ,电子从活性较强的金属流向相对惰性的金属 The less noble metal become the anode will be disolved 活性较强的金属这时做阳极 -被溶解 On the nobel metal for example gas will be generated 惰性金属上会有副产物生成，如 :气体 Contact corrosion What is contact Corrosion? G. Krolik - Guangzhou China - 201
5、5/12/11 4 less noble noble e (+) (-) Me1+ H2 Proprietary and Confidential G. Krolik - Guangzhou China - 2015/12/11 Contact corrosion - Oil distribution pipe in humid environment 接触 腐蚀 -如在潮湿环境中的油管 - Contact of materials with different electrochemical potential 化学电位各不相同的金属接触 Brass 黄铜 Aluminium铝 Unallo
6、yed Steel 非合金钢 Copper铜 5 Contact corrosion What is contact Corrosion? Proprietary and Confidential General Metal Finishing Electrochemical potential 电位差 Proprietary and Confidential The standart potential is measured under standart conditions 标准电势需要在特定标准条件下测试 。 Ion activity 1 (1 mol/l) 离子活性 1 Temper
7、ature温度 25C Barometric pressure气压 101,325 kPa ph = 0 Reference electrode standard hydrogen electrode 参考电极为标准氢电极 Contact corrosion Electrochemical potential Standard potential 电位差 标准电势 G. Krolik - Guangzhou China - 2015/12/11 7 Proprietary and Confidential Measuring equipment 测量设备 G. Krolik - Guangzh
8、ou China - 2015/12/11 8 Contact corrosion Electrochemical potential Standard potential Metal金属 e.g. silver (Ag) Standard hydrogen electrode 标准氢电极 Ion concentration of metal ion 金属离子浓度 1mol/l e.g. Ag+ pH = 0 p = 101,325 kPa Proprietary and Confidential G. Krolik - Guangzhou China - 2015/12/11 9 Volt
9、Au + 1.7 Ni + 0.25 H2 0 - 0.41 - 0.76 Zn - 1.66 Mg - 2.4 Contact corrosion Electrochemical potential Standard potential Fe Al Proprietary and Confidential The electrochemical potential change if the environment change 金属电位随环境变化而变化 Ion activity mol/l 离子活度 Temperature C 温度 Barometric pressure kPa 气压 p
10、H Chloride content 氯离子含量 etc. Contact corrosion Electrochemical potential Practical potential G. Krolik - Guangzhou China - 2015/12/11 10 Proprietary and Confidential G. Krolik - Guangzhou China - 2015/12/11 11 Volt Cu + 0.34 Ni + 0.25 H2 0.00 - 0.44 - 0.76 Zn - 1.66 Mg - 2.40 Contact corrosion Elec
11、trochemical potential Practical potential Fe Al Standard potential 标准电势 Volt Cu + 0.10 H2 0.00 - 0.21 - 0.85 Zn - 0.40 Volt Cu + 0.001 Ni + 0.04 H2 0.00 - 0.38 - 0.78 Zn on steel 铁基镀锌 - 0.71 Mg - 1.70 Water水 pH = 6 (no Cl-不含氯离子 ) (Al) Steel铁 (steel铁 ) (Al) - 1.30 Mg Sea water盐水 pH = 7.5 () with pass
12、ive layer 镀层 +钝化 + 0.07 Ni Proprietary and Confidential General Metal Finishing Contact corrosion test 接触腐蚀测试 Proprietary and Confidential VDA test Measuring of weight loss 腐蚀失重 Appearance外观 Contact corrosion Contact corrosion Test 接触腐蚀测试 G. Krolik - Guangzhou China - 2015/12/11 13 50 Test screw 测试螺
13、栓 tightening torque 拧紧扭矩 MA = 3-5 Nm Test material 测试 材料 (Al-, Mg-alloy) POM plastic qube POM塑料测试方块 25 30 3 35 Test screw测试螺栓 PA screw and washer 尼龙螺栓和垫片 Proprietary and Confidential Weigth loss 失重 Clean the metall sheet and dry it 清理金属块并吹干 Weigth the metall sheet 称重 Assamble the metall sheet with t
14、he test srew on the plastic qube 将测试螺栓和金属块拧紧固定在塑料方块上 Teightening torque扭矩 3 Nm 5 Nm NSS test 中性盐雾测试 Disassemble the screw and metal sheet 拆分螺栓和金属块 Clean the metal sheet with water and dry it 用水清洗金属块 ,并吹干 Weight the metal sheet again an determine the weight loss 再次测量金属块重量 ,并 计算质量损失 To determine the n
15、atural corrosion in NSS test assemble sheets with PA screw and determine the weight loss 计算在中性盐雾试验中 PA螺栓的自然腐蚀和质量损失 G. Krolik - Guangzhou China - 2015/12/11 14 Contact corrosion Contact corrosion Test procedure weight loss Proprietary and Confidential Determination of the contact corrosion by visual
16、check 目视观察接触腐蚀 Clean the parts and dry it, evaluate the contact corrosion visual 清洗并吹干样件 ,目视观察接触腐蚀 G. Krolik - Guangzhou China - 2015/12/11 15 Contact corrosion Contact corrosion Test procedure visual determination MgAZ91D + PA screw - - No contact corrosion 无接触腐蚀 Mg AZ91D + zinc covered, passivated
17、 screw with sealer - Medium contact corrosion Mg AZ91D+镀锌 /钝化 /封闭螺栓 中等腐蚀 MG AZ91D + zinc covered passivated screw - High contact corrosion Mg AZ91D+镀锌 /钝化螺栓 高 度 腐蚀 Proprietary and Confidential General Metal Finishing Coating for fastener in contact with aluminum and aluminum alloy 当紧固件接触铝 /铝合金 时如何 选
18、择表面处理 工艺 Proprietary and Confidential G. Krolik - Guangzhou China - 2015/12/11 17 Contact corrosion Electrochemical potential Practical potential ZnNi Steel铁 (Al) Sea water 海水 pH = 7.5 - 0.60 ZnNi (12% -14%) Volt Cu + 0.001 Ni + 0.04 H2 0.00 - 0.38 - 0.78 Zn on steel 铁基镀锌 - 0.71 Mg - 1.70 High poten
19、tial difference between steel and aluminum high contact corrosion potential铁和铝之间的电势差较高 -接触腐蚀较严重 If the protection layer of the steel part is destroyed - corrosion of aluminum is increased 当金属基材的保护镀层被破坏后 , 增加了铝腐蚀 Corrosion resistance of ZnNi layer are 10 times higher than zinc - delayed time until co
20、ntact corrosion starts! 锌镍合金的防腐蚀能力比镀锌高 10倍多 从而延迟接触腐蚀的发生！ Proprietary and Confidential G. Krolik - Guangzhou China - 2015/12/11 18 Contact corrosion Reduced contact corrosion ZnNi versus Zn - NSS test Zinc passivated 镀锌 +钝化 Zinc nickel passivated 锌镍合金 +钝化 120 h 240 h 720 h Proprietary and Confidentia
21、l G. Krolik - Guangzhou China - 2015/12/11 19 Weight loss after 720 h NSS: 4.02 mg/cm2 0.84 mg/cm2 Contact corrosion Contact corrosion Zn versus ZnNi in contact with AlMg3,5Mn Zinc passivated 镀锌 +钝化 Zinc nickel passivated 锌 镍合金 +钝化 120 h 240 h 720 h Proprietary and Confidential 20 G. Krolik - Guangz
22、hou China - 2015/12/11 00.511.522.533.544.5Screw: Zn passivated ZnNi passivated PA screw 紧固件 : 镀锌 +钝化 锌镍 +钝化 PA螺栓 Weight loss 失重 (mg/cm2) Contact corrosion Reduced contact corrosion ZnNi versus Zn Contact corrosion of AlMg3.5Mn in contact with zinc/zinc nickel plated and passivated screw 电镀锌 +钝化 ,电镀
23、锌镍 +钝化的紧固件在与 AlMa3.5Mn的接触腐蚀 Proprietary and Confidential General Metal Finishing Coating for fastener in contact with magnesium and magnesium alloy 接触材料是镁 /镁合金时如何选择紧固件的表面处理工艺 Proprietary and Confidential G. Krolik - Guangzhou China - 2015/12/11 22 Contact corrosion Electrochemical potential - Magnes
24、ium steel (Al) Sea water 海水 pH = 7.5 - 0.60 ZnNi (12% -14%) Volt Cu + 0.001 Ni + 0.04 H2 0.00 - 0.38 - 0.78 Zn on steel - 0.71 Mg - 1.70 High potential difference between steel and zinc nickel high contact corrosion potential铁和锌镍合金的电位差很高 -接触腐蚀相对较严重 Risk of contact corrosion by using ZnNi plated fast
25、ener采用锌镍合金时发生接触腐蚀的风险较高 Use of Zn plated and passivated parts with 2 x sealer application (high electrical resistance)采用 镀锌 +钝化 +2X封闭 (降低导电性 ) Proprietary and Confidential 23 Fasteners in contact to Magnesium VW/ Audi TL194 Unizinc ACZ / Unifix ZN 3-15 L / Sealer 300 W / Sealer 300 WL blind Reference
26、 Zn passivated Zn / passivated / 2x sealed ZnNi / passivated / sealed Contact corrosion on alloy Mg AZ91D: after 168 h NSS Magnesium dissolution is inferior when zinc instead of ZnNi is used! G. Krolik - Guangzhou China - 2015/12/11 Contact corrosion Electrochemical potential - Magnesium Proprietary
27、 and Confidential 24 G. Krolik - Guangzhou China - 2015/12/11 051015202530Fasteners plating Coating process Contact corrosion zinc to magnesium 0,20 % 0,10 % 0,08 % Standard Atotech Process Blind Weight loss 失重 (mg) Proprietary and Confidential Aluminum and aluminum alloy 铝和铝合金 Use of ZnNi plated fa
28、steners 采用锌镍合金电镀的紧固件 Increase time until the protection layer of the fastener is corroded (high contact corrosion between aluminum/-alloy and steel!) 增加测试时间知道紧固件上的镀层被腐蚀 (铝 /铝合金和铁基材的接触腐蚀更严重 ) Low contact corrosion between aluminium/-alloy and ZnNi layer 紧固件上的锌镍镀层和铝 /铝合金接触腐蚀程度较轻 Magnesium/-alloy 镁 /镁合
29、金 Use of Zn plated fasteners 采用镀锌的紧固件 Contact corrosion between magnesium/-alloy and zinc plated fasteners lower than to ZnNi plated parts电镀锌的紧固件接触镁 /镁合金时比用电镀锌镍的紧固件腐蚀程度轻 Use increase layer thickness of sealer to avoid contact corrosion between fastener and magnesium/-alloy可以增加封闭层厚度来减少和避免紧固件和镁 /镁合金的接触腐蚀 G. Krolik - Guangzhou China - 2015/12/11 25 Contact corrosion Summery 总结 Proprietary and Confidential General Metal Finishing Thank you very much for your attention! 非常感谢 ！
