1. Zinc

2. Resistance Welding Learning Activities View Slides; Lesson Objectives
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Lesson Objectives
When you finish this lesson you will understand:
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3. Specific Gravity 7.14, slightly less than iron
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
Listed here are some of the properties of zinc and zinc alloys. Its specific gravity of 7.14 makes it slightly lighter than iron, but it has a low melting and boiling temperature. The electrical conductivity makes zinc fit in between that of copper and steel. The zinc alloys are generally supplied in two types, cast and rolled alloys. The alloys are very brittle at room temperature so elevated temperature rolling is required. But the zinc alloys have recrystalization temperature at or below room temperature so they dynamically recrystalize. This softens the alloy and requires that low heat input process be used to reduce the HAZ softening. The sheet surface is generally mechanically abraded to clean it before spot welding.

4. Chemical Processing Applications
Uses
Cast forms
Roofing
Chemical Processing Applications
Zinc is used in cast form, generally zinc die castings, in sheet form for applications like roofing material and used in chemical processing plants.

5. Cast alloys are designated by number (e. g. 2, 3, 5, 7, etc
Cast alloys are designated by number (e.g.. 2, 3, 5, 7, etc..) The compositions are presented here. The major alloying elements are aluminum and copper.

6. Wrought alloy compositions are presented here.

7. 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
Resistance welding can provide sound welds with the least heat input compared to gas or arc welding. Resistance welding using either spot or seam welding, is always done on lap or flange joints. The thickness of the sheet dictates the minimum overlap of the joint. Joint areas must be thoroughly cleaned and abraded. Cleaning methods include grinding, machining, buffing, and abrading with emery board or sandpaper. All have given good results and should be followed by degreasing if necessary. As with most metals the area to be fused into the weld should be clean and free of any foreign material. Solid zinc strip alloys may be resistance welded with currents near equivalent with steel and low electrode forces. Compare to steel, zinc alloys have approximately twice the electrical conductivity, much lower melting ranges, approximately the same specific heats and higher thermal conductivity. Because of the softness and generally greater thickness of zinc alloy work-pieces, a low inertia follow-up for welding electrode control is needed. Internal defects (cavities) are common but these can be minimized by using a forging force.

8. As with the zinc coated steels, the zinc can alloy with the copper electrodes and thus reduce electrode life as indicated by this phase diagram. Cu Zn

9. Rolled Alloy Spot & Seam
Here are typical micrographs of the spot and seam weld on zinc alloys. Note that the zinc alloys tend to form pores (both spot and seam) because of the very low vapor pressure of zinc.
Rolled Alloy Spot & Seam

10. Cast Alloy Spot & Seam Weld
Similar micrographs are presented here for spot and seam welds mad on cast zinc. Note that the porosity is somewhat more extensive.
Cast Alloy Spot & Seam Weld

11. Electrode: class 2 with 3 in radius dome
Listed here are typical spot weld parameter schedules for the zinc-Copper-Titanium Alloy.
Electrode: class 2 with 3 in radius dome

12. Electrode: class 2 with 15 degree bevel and face radius of 3 inches
Listed here are the schedules for seam welding of the Zinc-Copper -Titanium Alloy.
Electrode: class 2 with 15 degree bevel and face radius of 3 inches

13. 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
Several recommendations for the welding of cast zinc alloys are to start with the parameter set up for rolled alloys and adjust from there. Since the castings generally have extra coatings applied, it is good practice to remove these before welding.