Zinc

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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.

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.

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.

Wrought alloy compositions are presented here.

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.

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

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

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

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

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

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.