1. Aluminum Coated Steel

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. Aluminized Coated Steel
Hot Dipped (continuous or batch)
Electroplated
Thermal Spraying
Powder Coating with Fusion
Diffusion Coating
We will consider these
Aluminum coated steel, like the other coated steels, provides a corrosive protection to the steel sheet. There are some additional benefits that we will see below also. The aluminum protective coating is applied in several different ways including hot dipping, electroplating thermal spraying and power coating with subsequent heating to fusion. In addition, a subsequent temperature diffusion treatment can be applied to the coating as well. We will consider only the hot dipped coating and the subsequent diffusion coating as these are the most prevalent.

4. Hot Dipped Aluminum Coating Lower Electrical Resistance
Type 1: Al - 8% Si (Oxidation Resistance Up to 1200F - 649C)-
Reduced Formability
T1-40 = 0.40 oz/ sq ft (0.001 inch thick)
T1-25 = 0.25 oz/ sq ft ( inch thick)
Type 2: Commercially Pure Al (Atmospheric Resistance at RT)
Lower Electrical Resistance
0.75 oz/ sq ft (0.002 inch thick)
[Aluminum Coated] Aluminum coated steel is produced by hot-dip coating cold rolled sheet steel on continuous lines. It provides a material with the superior strength of steel and the surface properties of aluminum. There are two types as illustrated here. Type 1 contains up to 8% Si in the coating and finds particular use for elevated temperature oxidation; and type 2 is essentially commercially pure aluminum coating.

5. Hot Dipped Aluminum Coating Type 2
This is a cross section of a type 2 (pure aluminum) hot dipped aluminum coating. Note that the pure aluminum is on the top. Some darker spots of aluminum-iron inter-metallic can be seen in this aluminum. The middle region is an iron-Aluminide inter-diffusion phase. And the iron is at the bottom.
Iron-Aluminide Fe
ASM Handbook , Vol 1, 1990

6. Typical Applications of Coated Steels
Aluminum Coated
Automotive exhaust systems
The aluminum coated steels find a lot of use in the manufacture of automotive exhaust systems.

7. Diffusion Aluminizing
Pure Aluminum Coating Diffusion Heat Treatment
(Applied by Any of the previous processes) (Furnace Heat Treatment)
The diffusion coating is produced by post-coating anneal to promote interdiffusion of the aluminum into the steel. No free aluminum remains on the surface, but a complex diffusion zone of iron-aluminum inter-metallic compounds is formed.

8. The diffusion aluminized coating can be applied to a range of materials as seen in this table. Note the uses of the diffusion aluminized carbon steels.
AWS Welding Handbook

9. Welding Hot Dipped Aluminum Coated Steel

10. Welding Aluminum Coated Steels
Spot Welding
Welding Current 20-50% higher than uncoated steel
Electrode Force 20-50% higher than uncoated Steel
Weld Time 40-60% longer than uncoated steel
Electrode Dressing somewhat more frequent than Galvanized Steel
Class II Truncated Cone Electrodes have been successful
More electrode indentation with type 2 Aluminized Sheet because it has lower resistance than type 1 Aluminized & generally Thicker Coating
The table here list some observations about the spot welding of the hot dipped aluminum coated steels. Because of the aluminum, the currents are higher than uncoated steel, the silicon free coatings with the somewhat lower electrical resistance are the highest current; electrode forces are grater and weld time longer. Somewhat more electrode wear is observed than with the zinc coated galvanized steels.

11. This table lists some nominal parameters for welding the hot dipped aluminized steels.
AWS Welding Handbook

12. Welding Aluminum Coated Steels
Projection Welding
Benefit of Projection Welding:
Reduces need for frequent electrode dressing
Type 1 coating
Recommend slightly larger projects than for Uncoated steel
Normally flat class II Electrodes Recommended
These are some observations regarding projection welding of the hot dipped aluminized steels.

13. Welding Aluminum Coated Steels
Seam Welding
AWS Recommendations:
% greater welding current than bare steel
% greater pressure than bare steel
Class II wheels wit Type 1 Material
Pick up of Aluminum on Wheel must be countered
Knurled Drive Wheel
Power Brushes
Large amount of flood water
Mash seam welding is sometimes hampered by the refractory Oxide present
These are observations for seam welding of the hot dipped aluminized steels.
AWS Welding Handbook

14. ERW & High-Frequency Seam Welding
Welding Aluminum Coated Steels
ERW & High-Frequency Seam Welding
Both 60 Hz and High Frequency Welds can be made
Edges must be square & free of Aluminum to prevent Aluminum Oxide, thus Centerline defects
These are some observations for the ERW and High Frequency welding of hot dipped aluminized steel.

15. Welding Diffusion Aluminized Metals

16. Welding Diffusion Aluminized Metals
Close to the same as welding uncoated steel with one exception noted below
Aluminum Above 1% in the Weld Can Significantly Reduce Ductility and Cause Embrittlement
The resistance of the diffusion treated aluminized steels is considerably higher than the non-diffusion transformed alloy layer present in the diffusion aluminized steels. Because of this, the welding parameters are close to those of the uncoated steel. There is one exception, aluminum in the solidified weld metal can cause embrittlement.