I'm doing my thesis on electro-deposition of Zn-Ni on Mg AZ91D alloy. I tried to coat the substrate by the following experimental way and the result turned out to be bad, the Zn-Ni coating was very brittle and lacked adherence to the substrate.
Process sequence which I followed,
1.Polishing
2. Activation in citric acid (100g/l), T=25°C, t= 45 sec
3.conditioning in sodium hydroxide (200g/l), T= 65°C,t=30min
4.Dilute cleaning in citric acid (10g/l), T=25°C,t=10sec
5.Zinc immersion, T=80±2°C,t=6min, compsition is as follows
- Zinc sulphate – 30g/L
- Potassium pyrophosphite– 110 g/L
- Sodium fluoride – 5 g/L
- sodium carbonate - 5 g/L
6.Electroless Ni plating, T=80±2°C,t=1hr, compsition is as follows
- Nickel sulphate – 15g/L
- sodium acetate– 13g/L
- sodium hypophosphite - 14 g/L
- Ammonium hydrogen difluoride - 8g/L
- Thiourea - 1 mg/L
- Hydroflouric acid - 12 ml/L
The use of chromium trioxide is banned in my laboratory and so I couldn't use it in the pretreatment. Kindly suggest me some alternative pretreatment steps/eletroless process to get a better Zn-Ni deposit on Mg. Any comments or tips would highly be appreciated, also I'm attaching the pic of my processed sample.
Dear Vinoth,
EN coating on magnesium alloy components can enhance the wear and corrosion performance of the components greatly. This is a good research. For your kind perusal, I am attaching 1 short review article published in Dec 2014. Hope this help.
Dear Vinoth
You can use electroplating, hot spraying and atomaization.
Best Regards
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