Finishing Workshop. Acid Etch Alloy Response. Introduction 5/1/2017. Acid Etch Overview. Alloy Study Weight Loss Gloss Wall Thickness.

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1 Finishing Workshop Columbus, Ohio May 16-17, 2017 Acid Etch Alloy Response Introduction Acid Etch Overview Alloy Study Weight Loss Gloss Wall Thickness Conclusion 1

2 Acid Etch Overview Acid etch is an alternative chemical etch process to replace the conventional caustic prior to aluminum anodizing. It produces a premium matte finish at low gloss values with minimum aluminum dissolution. Acid Etch Overview At specific acid etch conditions, the fluoride ions attack the aluminum surface producing unique, smooth grain boundaries. The result is a unique and attractive matte etch finish. The reaction results in dissolving less than 1.0 gram/sq. ft. of aluminum from the surface. That aluminum is precipitated as aluminum fluoride in the form of sludge. Conventional no-dump etch baths remove approximately 10 grams/sq. ft. of aluminum from the surface for a 10 minute caustic etch. Acid Etch Process Requirements Tank Filtration/purification system Heating source Exhaust/scrubber system Agitation 2

3 Acid Etch Advantages Acid etch produces an excellent uniform matte finish Excellent at removing and/or minimizing extrusion lines and mild scratches Can produce very low gloss readings ( ) Can also produce gloss readings between Significant reduction in the etch time, only minutes compared to minutes Significant reduction of aluminum removal. Less than 1.5 grams/sq. ft. compared to 10 grams/sq. ft. in caustic etch Acid Etch Advantages Significant reduction of waste sludge Extends the life of the process racks Acid etch is not sensitive to zinc contamination. 5.0 PPM zinc in caustic etch causes severe galvanizing problems Acid etch produces less fumes than the caustic process No boil-over with acid etch Secondary billet can be used with acid etch Easy rinsing. Minimal sludge in rinse Acid etch does not require cooling Acid Etch Disadvantages Cannot be use to strip anodic coating Does not remove graphite or pick-up High production lines must use powder product Electro-color is more sensitive to smut formation 3

4 Acid Etch Metal Trends Weight Loss The majority of metal loss occurs within the first sixty seconds Weight loss peaks, then quickly drops off Gloss Gloss follows a similar trend Gloss will decrease dramatically within the first sixty seconds then tapers off Wall Thickness Acid etch removed inches to inches per side Caustic etch removed inches to inches per side Alloy Study Alloy Study After switching to acid etch, anodizers began to observe differences in gloss between acid etch parts Was this simply due to the shape of the part, oxide thickness or was it the result of different alloys This study was created to determine the impact of the etching process on many different alloys Etching would be in both acid and alkaline baths for comparison The alloys used were evaluated for weight loss, gloss and wall thickness 4

5 Alloys Tested 6063 Medium-strength alloy (referred to as an architectural alloy) 6060 Medium-strength alloy with strength slightly lower than Bright-dip alloy 6005A Medium-strength alloy with properties between 6061 and Medium-strength alloy with properties between 6061 and Medium- to high-strength alloy with strength higher than 6005A 6082 Medium- to high-strength alloy with the highest strength of the 6xxx-series alloys Medium-strength alloy with good workability properties 5005 Medium- to high-strength alloy with relatively high welded strength compared to other alloys 2024 High copper alloy, used in applications requiring high strength to weight ratios and good fatigue resistance 7075 Strong alloy with strength comparable to many steels, good fatigue strength and average machinability *Metal provided by Bonnell Aluminum Newman, GA, Southern Aluminum Atlanta, GA and ACT Alloys Tested - Hardness Alloys Temper 6063 T T T A 6005 T T T T6 Process Controls 5

6 Weight Loss Weight Loss This test was designed to determine if there is a weight loss between a variety of alloys. Pieces of each alloy were cut, cleaned and weighed Several pieces from each alloy were placed in the acid etch for 3 minutes Another set of parts from each alloy were placed in a caustic etch for 10 minutes All parts were deoxidized, rinsed, dried and re-weighed Weight Loss 120 Weight Loss Comparison Between Caustic and Acid Etch Weight Loss (mg / in 2 ) A Alloy Weight Loss from Caustic Etch Weight Loss from Acid Etch 6

7 Weight Loss Summary The alloys processed through the acid etch had a metal loss range of 6 mg/in 2 The alloys processed through the caustic etch had a metal loss range of mg/in 2 Weight loss trends were similar between both acid and caustic etch however much lower with acid etch 6060 had the most of weight loss when processed through the acid etch or caustic etch Weight Loss Summary 6463 had the least amount of weight loss when processed through caustic etch 7075 had the least amount of weight loss when processed through acid etch 6061 and 6463 alloys had a higher copper content and lower iron content when compared to the other alloys 7075, a high zinc alloy and one of the strongest aluminum alloys, produced results very similar to 6061 Gloss 7

8 Gloss This test was designed to determine the gloss difference between a variety of alloys. Pieces of each alloy were cut and cleaned Several samples from each alloy were placed in the acid etch for 3 minutes with a 30 second caustic clean-up Another set of samples from each alloy were placed in a caustic etch for 10 minutes All parts were anodized to a 0.7 mil thickness and sealed Gloss readings were taken from each piece after anodizing Gloss Final Gloss Reading By Etching Process Gloss Reading (60 0 ) A Alloy Acid Etch Final Gloss After Anodizing Caustic Etch Final Gloss After Anodizing 6063 and

9 6005 and 6005A 6463 and and

10 7075 and Gloss Summary Acid etch gloss fluctuated 5.1 points between all alloys Caustic etch fluctuated 26.5 points between all alloys 2024 had the highest gloss when processed through caustic etch 7075 had the lowest gloss when processed through caustic etch 6005A had the highest gloss when processed through acid etch 3003 had the lowest gloss when processed through acid etch Caustic etching produced a lower gloss on 7075 than acid etching 10

11 Wall Thickness Wall Thickness Wall thickness was checked before and after etching with a micrometer for both acid and caustic etch Metal removal was consistent across the alloys tested within each type of etch Acid etch removed inches per side Caustic etch removed inches per side Conclusion 11

12 Conclusion There is definitely a different metal response when processing a variety of aluminum alloys. Different alloys respond differently in acid and caustic etch The finish can be dramatically different between parts based on the type of etch used Weight loss trends were similar between both acid and caustic etch however much lower with acid etch Alloys that had a higher copper content and lower iron content had the least amount of weight loss when processed through acid and caustic etch Conclusion Acid Etch removes significantly less aluminum than caustic etch. Across the alloys processed, acid etch had a metal loss range of 6.0 mg/in 2 while caustic etch had a metal loss range of mg/in 2 Acid etch produced more consistent gloss Across the alloys processed, acid etch gloss fluctuated 5.1 points between all alloys while caustic etch gloss fluctuated 26.5 points between all alloys Know your alloys! Acknowledgments The aluminum used for this study was provided by Bonnell Aluminum Newnan, GA, Southern Aluminum, Atlanta, GA and ACT Thanks to Houghton Chemists Nathan Sheffield, Bruce Thomas and Ken Wilson 12