Zinc

Resistance Welding

Lesson ObjectivesWhen you finish this lesson you will understand:•

Learning Activities1. View Slides; 2. Read Notes, 3. Listen to lecture4. Do on-line workbook

Keywords

Zinc• Specific Gravity 7.14, slightly less than iron• Low melting temp 787F (419C)• Low boiling temp 1665F (907C) - Fuming, Vapor• Electrical Conductivity 25% of Copper (2 x steel)

Zinc Alloys• Two Alloy Types

• Cast Zinc• Rolled Zinc

• Zinc Alloys Brittle at RT, elevated temp mechanical working• Zinc Alloys have recrystallization temp at or below RT• Recrystallization reduces strength in rolled alloys• Use low heat input to reduce HAZ Softening (Resistance Weld)• Mechanical Clean & Abraded to clean surface

Uses• Cast forms• Roofing• Chemical Processing Applications

Resistance Welding of Rolled Alloys

Spot & Seam Welding• Equivalent or Slightly Lower Current than steel (lower resistance, lower melting temp)• Lower Force than steel (softer)• Low inertia head, more indentation needs faster follow-up• Disp Strengthened Electrodes, High alloying with copper• Mechanical clean surface• Internal defects or cavities common, low boiling point

•Forge force can help

Seam Welding• Increased roll speed requires increased current

Cu Zn

Rolled Alloy Spot & Seam

Cast Alloy Spot & Seam Weld

Electrode: class 2 with 3 in radius dome

Electrode: class 2 with 15 degree bevel and face radius of 3 inches

Resistance Welding of Cast Zinc Alloys

• Start with the same recommendation as Rolled Alloys• High Resistance Films (electro-deposited & others) Removed

The castings generally have extra coatings