Most aluminum alloys will build aluminum oxide in an anodizing tank, so the answer to this question depends on the anodizing process and the desired result.
- Copper containing 2000 series are generally the most difficult to anodize and 5000 or 6000 series are the easiest.
- SAF recommends 5005 aluminum alloy for sheet 6063 aluminum alloy for extrusion.
This chart from the Aluminum Anodizers Council is a useful guide.
|Aluminum Alloy Series (AA)*||Alloying Constituents||Metal Properties||Anodized Coating Properties||Uses||A.Q.** Types||Non-A.Q.** Types||Aluminum Alloy Finishing Advice|
|1XXX||none||soft, conductive||clear, bright||cans, architectural||none||1100, 1175||Care should be taken when racking this soft material good for bright coatings susceptible to etch, staining|
|2XXX||Copper||very strong, hard, low elongation||yellow, poor protection||aircraft, mechanical||none||2011, 2017, 2219, 2224||Since copper content is >2%, these produce yellow, poor weather-resistant coatings. Don’t mix with other alloys on load|
|3XXX||Manganese||strong, small grain||grayish-brown||cans, architectural, lighting||none||3003, 3004||Difficult to match sheet-to-sheet (varying degrees of gray / brown). Used extensively for architectural painted products|
|4XXX||Silicon||strong, fluid||dark gray||architectural, lighting||none||4043, 4343||Produces heavy black smut which is hard to remove 4043 & 4343 used for architectural dark gray finishes in past years|
|5XXX||Magnesium||strong, ductile, fluid||clear, good protection||architectural, welding wire, lighting||5005, 5657||5052, 5252||for 5005 – keep silicon <0.1% and magnesium between 0.7% and 0.9%, maximum of +/- 20% for job watch for oxide streaks|
|6XXX||Magnesium & Silicon||strong, ductile||clear, good protection||architectural, structural||6063, 6463||6061, 6101||Matte – iron >0.2%, bright – iron <0.1%, 6063 best match for 5005, 6463 best for chemical brightening|
|7XXX||Zinc||very strong||clear, good protection||automotive||none||7029, 7046, 7075||Zinc over 5% will produce brown, tinted coatings, watch zinc in effluent stream, good for bright coatings|
Source: Aluminum Anodizers Council (AAC) Technical Bulletin #2-94, Aluminum Alloy Reference for Anodizing