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Aluminum Coated Steel.

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Presentation on theme: "Aluminum Coated Steel."— Presentation transcript:

1 Aluminum Coated Steel

2 Resistance Welding Learning Activities View Slides; Lesson Objectives
Read Notes, Listen to lecture Do on-line workbook Lesson Objectives When you finish this lesson you will understand: Keywords

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.

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