Slide 003: Shielding Gases, Filler Metals & Material Compatibility

Slide Visual

Slide Overview

This slide covers the selection of shielding gases and filler metals for MIG and TIG welding. Correct selection is critical for weld quality — wrong gas or filler causes porosity, cracking, or weak joints.

Instruction Notes

Shielding Gas Selection

MIG Welding Gases:

Gas/Mix	Composition	Best For	Characteristics
C25 (75/25)	75% Ar / 25% CO₂	Mild steel (most common)	Good penetration, low spatter, all-position
C100	100% CO₂	Mild steel (budget)	Deep penetration, more spatter, hotter arc
90/10	90% Ar / 10% CO₂	Mild steel (spray transfer)	Smooth arc, less spatter, flat/horizontal only
Argon 100%	100% Argon	Aluminum, stainless	Required for non-ferrous metals
Tri-mix	90% He / 7.5% Ar / 2.5% CO₂	Stainless steel	Deep penetration, fast travel, specialty

TIG Welding Gases:

Gas	Use	Notes
Argon 100%	Steel, stainless, aluminum, most metals	Standard for all TIG welding
Argon/Helium (75/25 or 50/50)	Aluminum (thick), copper	Hotter arc for high-conductivity metals
Pure Helium	Copper, thick aluminum	Very hot arc, harder to control

Flow Rate: 15-25 CFH (cubic feet per hour) for most applications. Too low = porosity. Too high = turbulence pulls in air (also causes porosity). Draft/wind requires higher flow or gas lens.

Filler Metal Selection

MIG Wire for Steel: - ER70S-6: Most common mild steel wire. "70" = 70,000 PSI tensile strength. "S-6" = solid wire with silicon/manganese deoxidizers. Use with C25 gas. Available in 0.023", 0.030", 0.035", 0.045" diameters. - Wire diameter guide: 0.023"-0.030" for thin material (<⅛"), 0.035" for medium (⅛"-¼"), 0.045" for thick (¼"+)

MIG Wire for Aluminum: - ER4043: General purpose aluminum wire. Good flow, less crack-sensitive. For 6061, 5052 base metals - ER5356: Higher strength, better color match after anodizing. For 5xxx series and structural 6061

TIG Filler Rods: - ER70S-2: Mild steel TIG rod. Match to base metal grade - ER308L: Stainless steel TIG rod for 304 stainless base metal - ER316L: Stainless steel TIG rod for 316 stainless base metal - ER4043 / ER5356: Aluminum TIG rod (same alloys as MIG wire, but in straight rod form)

Material Compatibility Rules

1. Match filler to base metal: The filler must be metallurgically compatible. Never use carbon steel filler on stainless steel
2. Match or exceed base metal strength: ER70S-6 (70 ksi) for A36 steel (36 ksi yield / 58 ksi tensile) — filler is stronger than base metal
3. Dissimilar metals: Welding dissimilar metals (e.g., carbon steel to stainless) requires specialty filler (e.g., 309L) — consult welding engineer
4. Never weld: Zinc-coated steel without removing coating, lead-containing alloys, or unknown metals

Key Talking Points

1. C25 (75/25 Ar/CO₂) is the default MIG gas for steel — learn this first
2. 100% Argon is used for ALL TIG welding and for MIG aluminum/stainless
3. ER70S-6 is the universal mild steel filler — memorize this designation
4. Gas flow rate must be correct — both too low AND too high cause porosity
5. Never assume you know the base metal — verify before selecting filler

Learning Objectives (Concept Check)

• [ ] Select the correct shielding gas for 3 different welding scenarios
• [ ] Decode the AWS filler metal classification system (ER70S-6)
• [ ] Match filler metal to base metal for mild steel, stainless, and aluminum

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Last Updated: 2026-03-19