Metal Finishing Guide Book


Issue link:

Contents of this Issue


Page 156 of 843

Table XXII. Zinc Alloy Compositions Alloy % Zinc % Aluminum % Magnesium % Copper Pure 99.9+ — — — % Lead — Zamak 3 Balance 4.0 0.04 — — Zamak 5 Balance 4.0 0.04 1.0 — Zamak 2 Balance 4.0 0.03 3.0 — Slush Balance 4.75 — 0.25 — Slush Balance 5.5 — — — Drawn Balance — — — 0.08 4. Tarnish inhibit in dip application using either a soap (mechanical tarnish inhibit film) or a benzotriazole (active surface antioxidant). 5. Optionally lacquer (dip or electrolytic) or apply electrolytic chromate. Inconel This alloy constituent typically contains 13.5% nickel and 6.0% chromium. (Note: one alloy type may contain 2% silicon.) Surface preparation cycle: 1. Alkaline soak clean. Mild to moderate alkalinity with sufficient detergency. 2. Acid dip. 20-30% v/v hydrochloric acid for primary oxide removal. 3. Anodically etch. Wood's nickel strike, 100-120°F (38-49°C), 50 A/ft2, 20-30 sec. 4. Strike plate cathodic. Woods' nickel strike, 100-120°F (38-49°C), 50 A/ft2, 2-3 min. 5. Rinse well, proceed to plating bath. The above cycle is sufficient for Inconel X and Hastelloy C. Nickel and Nickel Alloys Require similar treatment as stainless steels. Anodically etch at 15 to 25 A/ft2 for 1 to 3 minutes in a 25% v/v sulfuric acid solution. Next, cathodically condition at 150 to 225 A/ft2 in the Woods' strike, or at 40 to 60 A/ft2 in a sulfuric acid/fluoride/chloride solution. Parts not long aged may also be activated in an immersion dip consisting of 5 tp 10% v/v sulfuric acid and 2 to 4 oz/gal of potassium iodide at 75 to 90°F (24-32°C). These treatments also apply for replating aged nickel plated parts and rejects. Powdered Metal Same recommended surface preparation steps as for cast iron. Rinsing is very important, to facilitate drainage and removal of previous contaminating solutions. Silver The metal and its alloys tarnish readily, forming a blackish oxide film. After soak cleaning in an appropriate caustic containing cleaner, dip in 5 to 10% v/v sulfuric acid to neutralize surface. Next, chemically polish in a solution consisting of 20 to 25% v/v hydrogen peroxide, at 85 to 100°F (29-38°C). Titanium Activation is the critical factor. The following cycle may be appropriate with 153

Articles in this issue

view archives of Metal Finishing Guide Book - 2013