What is the recommended chemical cleaning process and composition prior to electroless nickel plating for magnesium? I.C.
Magnesium is different than most ordinary metals that you may be used to cleaning. Degreasing and surface preparation prior to plating are usually done in a highly alkaline, aqueous cleaning bath. It is important to keep the pH of the bath at about 12 or higher, otherwise the base metal will start to etch. A simple cleaning composition would consist of about 4 oz/gal each of sodium hydroxide and sodium carbonate with a small amount of surfactant (anionic and nonionic, total about 0.1 oz/gal). Cleaning is done for 5-10 min at elevated temperature (usually about 180F). Rather than having to inventory and maintain these chemicals separately, it would probably be easier for you to contact your chemical supplier who would be able to provide you with a compound containing all the necessary ingredients. If electrocleaning is preferred, it can be done cathodically with a current density of about 10-50 asf at about 6 v.
Prior to plating, the substrate is often acid cleaned. This may consist of a chromic acid/nitric acid step at room temperature. Additionally, the magnesium may be activated with a hydrofluoric acid treatment or a phosphoric acid treatment with ammonium bifluoride prior to plating.