Surface Cleaning Guide

Material-specific surface preparation methods for laser welding. Proper cleaning prevents 80% of porosity defects and ensures consistent weld quality.

Cleaning Requirement Severity

MaterialSeverityTime WindowPrimary Concern
🔴 Titanium
Critical
< 1 hourOxygen contamination → embrittlement
🟠 Aluminum
High
< 1 hourOxide layer reformation
🟡 Stainless Steel
Medium
< 24 hoursOil residue → porosity
🟡 Carbon Steel
Medium
< 48 hoursRust → porosity
🟢 Cast Iron
Low
< 72 hoursSurface scale

Material-Specific Cleaning Procedures

Stainless Steel 304/316

Common Contaminants

Oil/grease, fingerprints, surface oxides, machining residues

Step-by-Step Procedure

  1. 1
    Degrease: Wipe with acetone or isopropyl alcohol (IPA) using lint-free cloth. Remove all oil and grease residues.
  2. 2
    Remove oxides: Use stainless steel wire brush or 180-320 grit sandpaper. Brush/sand in welding direction.
  3. 3
    Final wipe: Clean again with fresh solvent to remove particles from brushing.
  4. 4
    Air dry: Use clean compressed air (oil-free) to dry surface.
  5. 5
    Time window: Weld within 24 hours. Handle with clean gloves only.

Quality Check

Water contact angle >90°. White cloth wipe shows no contamination.

Aluminum 6061/5052

Common Contaminants

Critical: Aluminum oxide layer (Al₂O₃) - melting point 2072°C vs aluminum 660°C!

Method 1: Chemical Cleaning (Preferred)

  1. 1
    Alkaline cleaning: 10% NaOH solution at 60°C for 5-10 minutes. Removes oil and light oxide.
  2. 2
    Acid pickling: 30% HNO₃ (nitric acid) at room temperature for 2-5 minutes. Removes oxide layer completely.
  3. 3
    Rinse thoroughly: Multiple clean water rinses to neutralize acid.
  4. 4
    Final solvent wipe: IPA to ensure complete drying.
  5. 5
    CRITICAL: Weld within 1 hour - oxide reforms rapidly in air!

Method 2: Mechanical Cleaning (Quick Method)

  1. 1
    Degrease: Acetone wipe.
  2. 2
    Abrade: Use stainless steel wire brush (never carbon steel - embeds Fe particles) or 180 grit sandpaper.
  3. 3
    Weld immediately - within 15 minutes if possible.

Quality Check

Bright metallic surface. No discoloration or matte oxide layer.

Copper

Common Contaminants

Copper oxide (black CuO or green Cu₂O), oil, tarnish

Cleaning Procedure

  1. 1
    Acid pickling: 10% dilute sulfuric acid (H₂SO₄) soak for 5-10 minutes. Removes all oxide layers.
  2. 2
    Rinse and neutralize: Clean water rinse, then baking soda solution to neutralize acid.
  3. 3
    Acetone wipe: Remove any remaining residues.
  4. 4
    Heat dry: 100°C heating to completely remove moisture.
  5. 5
    Weld immediately: Copper oxidizes rapidly. Ideal if still warm from drying.

Alternative: Mechanical Polishing

Polish to bright metallic luster using fine sandpaper or polishing wheel. Weld within 5-10 minutes.

Titanium Ti-6Al-4V (Most Critical)

Critical Warning

Any contamination on titanium causes embrittlement. Blue/yellow weld discoloration = SCRAP. Clean room environment strongly recommended.

Ultra-Clean Procedure

  1. 1
    Alkaline degrease: Remove all oil and organic contaminants.
  2. 2
    Acid pickle: HF (hydrofluoric) + HNO₃ (nitric) mixture. Extreme safety precautions required!
  3. 3
    Ultra-pure water rinse: Multiple rinses with deionized water.
  4. 4
    Vacuum dry: Or use ultra-clean nitrogen blow dry.
  5. 5
    Handle with powder-free gloves: Any skin oil causes defects.
  6. 6
    Weld in clean room if possible: Minimize airborne contamination.

Quality Check: Water Break Test

Apply water to surface. Water should spread as continuous film (complete wetting). Any beading indicates contamination.

Cleaning Tools & Material Compatibility

Tool/MethodSuitable ForAvoid Using OnImportant Notes
Stainless Steel Wire BrushSteel, Stainless Steel, TitaniumAluminumAvoid cross-contamination between materials
Nylon/Plastic BrushAluminum, Soft MaterialsNoneWill not embed foreign particles
Sandpaper (180-320 grit)All MetalsNoneWeld immediately after use
Acetone/IPAUniversal DegreasingPlasticsUse in ventilated area
Acid PicklingAluminum, Copper, TitaniumNoneSafety equipment required

Cleaning Verification Methods

Visual Inspection

  • Uniform metallic luster
  • No visible oil film or fingerprints
  • No discoloration or oxide layers

Water Contact Angle Test

Apply small water droplet to cleaned surface:

  • Good: Angle >90° (high surface energy)
  • Poor: Water spreads/beads (contamination)

Solvent Wipe Test

Wipe surface with white lint-free cloth dampened with IPA. Cloth should remain clean with no visible residue.

Water Break Test (Titanium)

Pour water over surface. Should form continuous film without breaking. Any water beading = contamination = reject.

Best Practices & Common Mistakes

✅ Do's

  • Clean in ventilated area: Solvent vapors are hazardous
  • Wear appropriate PPE: Gloves, goggles, respirator for acid work
  • Use dedicated brushes: Never cross-contaminate between materials
  • Work clean to dirty: Start with solvent, then mechanical if needed
  • Handle with clean gloves: After cleaning, never touch with bare hands
  • Document procedure: Record cleaning method and time for traceability

❌ Don'ts

  • Don't use carbon steel brush on aluminum: Embeds Fe particles
  • Don't skip degreasing: Oil residue is #1 cause of porosity
  • Don't wait too long: Aluminum oxide reforms in <1 hour
  • Don't mix cleaning chemicals: Can create hazardous reactions
  • Don't assume "clean enough": If in doubt, re-clean

Safety Reminders

  • Always review SDS sheets before using chemicals
  • Acid pickling requires face shield, rubber gloves, and fume hood
  • Have neutralizing agent (baking soda) readily available
  • Dispose of chemical waste properly per regulations

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