Aluminum Coated Steel

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

Aluminized Coated Steel

• Hot Dipped (continuous or batch)• Electroplated• Thermal Spraying• Powder Coating with Fusion• Diffusion Coating

We will consider these

Hot Dipped Aluminum Coating

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 (0.0005 inch thick)

Type 2: Commercially Pure Al (Atmospheric Resistance at RT)Lower Electrical Resistance

0.75 oz/ sq ft (0.002 inch thick)

Fe

Iron-Aluminide

Al

ASM Handbook , Vol 1, 1990

Hot Dipped Aluminum CoatingType 2

Typical Applications of Coated Steels

• Aluminum Coated– Automotive exhaust

systems

Diffusion Aluminizing

Pure Aluminum Coating + Diffusion Heat Treatment (Applied by Any of the previous processes) (Furnace Heat Treatment)

AWS Welding Handbook

Welding Hot Dipped Aluminum Coated Steel

Welding Aluminum Coated Steels

• 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

Spot Welding

AWS Welding Handbook

Welding Aluminum Coated SteelsProjection 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

Welding Aluminum Coated SteelsSeam Welding

AWS Recommendations:• 20 - 50% greater welding current than bare steel• 20 - 50% 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

AWS Welding Handbook

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

Welding Diffusion Aluminized Metals

Aluminum Above 1% in the Weld Can Significantly Reduce Ductility and Cause Embrittlement

Welding Diffusion Aluminized MetalsClose to the same as welding uncoated steel with one

exception noted below