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Hard Chromium Plating on Bi-metallic Substrate

adv.    

2007

I would like to know the methodology for plating hard chromium on bimetallic engine valve having following configurations:-
1. Upper Half:- Inconel
2. Lower Half:- SAEJ775 UNSG86450 (Low Alloy Steel)Ni & Cr - 0.5% each

Currently I'm facing the problem of peel off after doing anodic etching in Chromic acid with & without sulphate.Please suggest!

Ravindar Nagar
Pistons & Rings - Ghaziabad, UP, India

Inconel as well as other alloys based on nickel, cobalt and other corrosion and heat resistant metals always develop a passive oxide layer on their surface when exposed to oxygen. Reverse etch accelerates such passivity. Before chroming, you need to activate in a special highly acidic chloride bath known as Woods strike and then chrome on forward polarity. This treatment forms a thin active layer of nickel. Cancel subsequent reverse etch and chrome w/o delay. The active condition will soon disappear if exposed to an oxidizing environment.

Guillermo Marrufo
Monterrey, NL, Mexico
2007

adv.