Cleaning Aluminum

PQCW – Workshops for Terrific Products    “While I would prefer to have been at in-person laboratories so I could have hands-on experiences with cleaning processes, I really liked the two-week virtual PQCW. “People with different functions within our company, including Strategic Sourcing, Project Management, and Manufacturing Engineering, attended. “We learned a lot; and we have made changes. We are refining our own cleaning requirements and putting together training programs.   “For example, we used the workshop to develop black light testing and fixtures; and we have already set up a one-hour “Parts Washing 101” training course. “The section about EPA amended TSCA had useful, timely information.”  Christian Johnson, Engineer, Yaskawa, participant, PQCW21 Overcome the Challenges of Cleaning Aluminum 1. 2. 3. 4. 5. 6. 7. Some Basics About Aluminum What Does Clean Aluminum Really Mean? Aluminum Cleaning Chemistry Common Process Issues Industry Examples Measuring Cleanliness of Aluminum Questions Why Aluminum…….. • • • • • • Lightweight, but alloys are strong as steel Excellent Conductor, Heat and Current Corrosion Resistant Easily Formed, Machined Sustainable – Easily Recycled Many Times Highly Decorative But…. Aluminum Is a Process Challenge Highly Reactive The reactivity of Aluminum can make cleaning Aluminum parts difficult, but we can also use it to our advantage in preparing surfaces for other finishing processes Aluminum Is a Process Challenge Many Different Alloys – Wrought •1000 series are essentially pure with a minimum 99% Al •2000 series are alloyed with copper •3000 series are alloyed with manganese •4000 series are alloyed with silicon •5000 series are alloyed with magnesium •6000 series are alloyed with magnesium and silicon •7000 series are alloyed with zinc •8000 series are alloyed with other elements which are not covered by other series – Ex Lithium International Alloy Designation System Aluminum Is a Process Challenge Many Different Alloys - Cast •1xx.x series are minimum 99% aluminum •2xx.x series copper •3xx.x series silicon, with added copper and/or magnesium •4xx.x series silicon •5xx.x series magnesium Addition of alloying elements •6xx.x unused series add more complexity to •7xx.x series zinc chemical compatibility •8xx.x series tin •9xx.x other elements The Aluminum Association, Cast Alloys What Does Clean Mean? We are really talking about a pre-treatment process In most aluminum finishing processes we must remove not only the organic soils(lubes, compounds) but the inorganic soils as well(surface oxides, corrosion products, scales) •Degreasing – Removes Organic Soils •Etching – Removes Oxides, Elemental Impurities, Improves Adhesion, Removes Stock(Metal) •Deoxidizing – Removes Oxides without removing stock, activation •Desmutting – Removes the smut that can form from etching process •Non-Etch surface also desirable for bright finish What Does Clean Mean? We are really talking about a pre-treatment process In most aluminum finishing processes we must remove not only the organic soils(lubes, compounds) but the inorganic soils as well(surface oxides, corrosion products, scales) • Anodizing • Chem Film(Cr+ Conversion Coatings) • Plating, Electroless Ni • Powder Coat • Electrolytic Coloring What Does Clean Mean? We are really talking about a pre-treatment process Degrease Only What Does Clean Mean? We are really talking about a pre-treatment process Degrease and Deoxidize What Does Clean Mean? We are really talking about a pre-treatment process Non-Etch Matte Etch Pre-Treatment pH is King Do I use acid or alkaline based products? It depends Pre-Treatment Cleaners Non-Etch(Non-Smut) Non-Etch (Inhibited) Pre-Treatment – Cleaning Alkaline •Phosphates No Etch(Can “Bite”) Free Rinsing, Low Residue, Discharge Concerns •Borates(Borax) Good No Etch, Cheap, Solubility Problems •Silicates(100%) Better No Etch, Prone to Sludge(pH), Hard to Rinse(residues) •Fatty Acid Soaps Best No Etch, Expensive, Acid Stability, Hydrophobic Film, Heavy Degreasing •Inhibited Caustic(Silicates) No to Mild Etch, Cheap, Sensitive to Time and Temp(Etch and Smut) Sludge •Inhibited Caustic(Amines, Other) Mild to Heavy Etch, Generally Require Post De-Smut Step Borax Based Cleaner Inhibited Caustic/Silicated Cleaner Pre-Treatment Acid Cleaners (Organic Acids vs Mineral Acids) Pre-Treatment – Cleaning Acids •Mineral Acids – Phosphoric, Fluoride Based, HF or Fluoroboric All Deoxidize, Mild to Medium Etch, Fluoride Accelerates Etch •Organic Acids – Citric, Sulfonic Acids (DDBSA, MSA) All Deoxidize, Used Properly Provide No Etch, Expensive • Not optimal for removing heavy soils, oils repel acids • Very good at removing the stearate lube family • Use can be alloy specific, so less flexibility • Can’t process other metals in process, ie Cu, Fe – Immersion Plating • Equipment compatibility more limited, Materials of Construction • Improved compatibility with many downstream Al processes Organic Acid Based Cleaners 7075 – High Zinc Alloy Pitting with Acid Cleaners Overcome the Challenges of Cleaning Aluminum Cleaning - Deoxidation Example Example: Conversion Coating Pretreatment Study, Alloy 2024‐T(High Copper), 6061‐T6 Application: MIL‐DTL‐5541 Corrosion Test: ASTM B117 Materials Qualification: MIL‐DTL‐81706 Process: • Acid based cleaner/deoxidizer #2 • Tap Rinse • Tri-Chrome Seal(Cr+3) • DI Water Rinse Results: Aluminum Alloy: 2024-T3 2024-T3 6061-T6 6061-T6 Set # Set #1 Set #2 Set #3 Set #4 Immersion Time Clean and Deox Tri-Chrome Seal 2.5 minutes / 5 minutes 5 minutes / 5 minutes 2.5 minutes / 5 minutes 5 minutes / 5 minutes Salt Spray Hours: 504 168 1176 1176 Pass/Fail: Pass Fail Pass Pass Story From The Field In-Line Degreasing for Anodizing Cleaner X2 45 Sec 45 Sec Repeat Each Tank(All Acid Based Chemistry) Acid Rinse Acid Rinse Alkaline cleaner dragging emulsified oils down the process Pain Points • Poor Cleaning • High Scrap Rate • Business Demand • “Poisoning” of the Bright Dip Tanks with Lube • Bright Dip Eruptions • Operator Exposure to Hazards, Rashes Bright Dip Remaining Anodizing Process Tanks Dirty Parts Solution • Change chemistry of cleaner(Acid) • Improved compatibility downstream • Improved chemical feeding • Improved oil removal from tanks • Overall cleaning improved • Scrap reduced 5X Aluminum Cleaning Process Improvement Example: Acid Cleaner for Deep Drawn Aluminum Standard Process: • Immersion Washer with Ultrasonics. • Strong alkaline(base metal attack) and silicated cleaners not allowed. • Hard to remove stearate lubes, neutral phosphate cleaners not effective • Post heat treatment causes defects with improper cleaning Improved Process: • Acid based cleaner • No base metal attack • High solubility of stearate lubes • Bright lustrous finish without attack or etch • No post heat treat issues Pre-Treatment Etching and Deoxidation Acid Etch(Phosphoric, Fluoride) Deox (Sulfuric, Citric, Ferric, Low F-) Alkaline Etch Removes Oxides Caustic Etch (Inhibited) Heavy Caustic Etch (NaOH) Etch = Remove Stock(Metal) Deoxidation = Remove Surface Metal Oxides Only Etch Pre-Treatment – Etch and Deoxidation •Caustic(NaOH) Course Etch, Significant Stock Removal, Generate Smuts, High Sludge •Inhibited Caustic Controlled Finer Etch, Less Stock Removal, Low to No Smut, High Sludge •Acid Fine Etch, Short Immersion Times, 10x Less Stock Removed, Low to No Smut Smuts are the reaction products, including intermetallic compounds, that become insoluble in the etch solution. These adhere to the metal surface and must be solubilized Deoxidation •Caustic(NaOH) Deox Happens as Part of Etch •Inhibited Caustic Deox Happens as Part of Etch •Acids Deox Can Be Accomplished Without Etch Pre-Treatment De-Smutting Nitric/Fluoride/Ferric Salts Overcome the Challenges of Cleaning Aluminum Pre-Treatment – De-Smutting Acids •Mineral Acids – Nitric, HF(including fluoride salts), Ferric Salts •Combo of All Three(3) Cover Most Alloys •Some Sulfuric/Peroxide Based, Not Robust, Light Smuts •Most Deoxidizers will De-smut, Not All De-Smutters will Deoxidize(HNO3) Process Issues - Rinsing The Dirty Rinse Tank Exposing clean parts to a dirty rinse tank results in….. Dirty Parts! The Rinsing step in Aluminum Cleaning is more critical than with most other alloys Poor Rinsing Example In this example the residues from the cleaner tank remain on the surface and “burn” into the surface during a heattreating step. Deionized Water HEAT? Poor Rinsing, Residual Contaminates Simple Solution, Continuous Clean Rinse Process Issues – Waiting to Clean The longer you wait to clean Aluminum The more difficult your cleaning process will be Hot rinses can cause uneven surface oxidation Overcome the Challenges of Cleaning Aluminum Process Issues – Waiting to Clean Example - Reactive Lubes Reactive Surface Contamination Sensitive Alloys, Aluminum, Copper, Brass, et al Lubricants can permanently damage the surface of parts if not removed in a timely manner. Oxidation, smutting, and chemical surface attack. Amine based lube attack on 6061 Alloy Measuring Cleanliness of Aluminum Water Break Test - Involves examination of a surface for the presence of a continuous water film that has no water breaks. If a water-break-free film of water is present, it is indicative of the absence of hydrophobic surface contaminants. Oils, greases, and water-insoluble organic compounds would be examples of hydrophobic contaminants. The water break test does not confirm the presence or absence of hydrophilic contaminants or oxides. Tests based on Surface Tension(Dynes Testing) have been used to determine the cleanliness of surfaces. Care must be taken to ensure the use of test solutions specific to the substrate surface. Overcome the Challenges of Cleaning Aluminum Practical Cleanliness Testing UV Detection If soils are doped with compounds that exhibit fluorescence, exposure of cleaned parts to ultraviolet light will confirm the presence or absence of residual soils. Measuring Cleanliness of Aluminum Fundamental Connection: Surface Science and Water Contact Angle HIGH CONTACT ANGLE MINUTES TO HOURS LATER DYNAMIC WETTING SECONDS LATER NEWLY CREATED SURFACE LOW CONTA CT ANGLE COMPLETE WETTING Overcome the Challenges of Cleaning Aluminum Practical Cleanliness Testing Contact Angle Example is standard Aluminum surface prep process Dirty Dynamic Wetting* Water Based Lube Solvent Degreased Residue Post Degreasing Deoxidation Chemical Etch Contact Angle measurement can be easily correlated to the surface preparation steps to determine cleanliness Contact Angle via Optical Measurement BTG Labs Surface Analyst Summary 1. Aluminum Alloys are Highly Sensitive to the Chemistry used in Cleaning Processes 2. Cleaning is Really About Surface Preparation 3. Pre and Post Cleaning Steps Are Critical 4. There are Practical Tools Available to Monitor the Cleanliness and Surface Properties of Aluminum