By OBEWAN
Date 06-18-2012 16:06
Edited 06-23-2012 17:28
Is there any other good etch for aluminum weld microstructures other than Keller's?
We have something that works for macros but we need a good swab etch for revealing microstructures and micro cracks. We want it to be a swab etch too.
Our chemist has issued dire warnings regarding the dangers of using HF in Keller's - including lung, heart and bone damage from the tiniest exposures. She is refusing to have anything to do with using the HF component.
We currently use NaOH and a 50 50 with Nitric and HCL I think but they are only good for macros so far and they leave the specimens too pitted to reveal any micro cracks.
We are welding 6050, 6080, 1010, and 1030 I think.
Steve
Steve, I'm not sure how much this differs from the current etchant you're using, but AWS D1.2, Annex H, indicates a basic etchant of 20% sodium hydroxide at 120F, rinse in clean water, If desmutting is necessary to reveal weld boundaries, a concentrated nitric acid dip at room temperature should be used. Rise thorougly. I would think you'd want to limit the time exposure in the acids to minimize pitting.
ASM International handbook Vol 9, 9th edition mentions an elecctrolytic etcch with Barkers reagent (4 -5 mL HBF4 (48%), 200 mL water. Use aluminum, lead or SS for cathode, specimen is anode. Anodize 40 - 80 s at approx. 0.2A/cm2 (1.3AA/in2, or about 20V dc). Check results on on microscope with crossed polarizer. Not sure if this etchant is practical for you, though.